BigBlog

This site specialises in the neglected subject of 'motorcycle crankcase breathing'. It publishes original research into crankcase breathing for classic, vintage and modern bikes. It reports developments with Bunn Breather technology. It shows a range of marque installations.

This index covers the 101 reports on this site to date. The reports are "stacked"  and spread over 2 pages. Reports 1-37 are on page 1. The more recent reports are near the top of the stack, on page 2 below.

The resource has reached 101 reports and photo galleries. Navigation is becoming less simple.  Reports are subject & colour-coded for easier selection.

How To Use Index- First note the report number you wish to read. Hit the "Down Arrow" at the bottom-right corner of your browser. Arrow down through the reports till you reach the one you want.  The reports are numbered so you  know where you are in the stack.  

Photo Galleries are so marked.  The copyright for written material on this Blog lies with  A.R.Bunn.  Such material may not be reproduced or published without prior consent.  Copyright © A.R.Bunn 2010

NB:- Formatting in some reports is poor, due to varying source docs and limited Blog tools.

Customer Service

Technical Breather Kit Enquires:-email rexbunn@bigpond.com

All Book and Author enquiries to- email rexbunn@bigpond.com

USA/Canada Breather Kit sales- email Mark Appleton at

British Cycle Supply Company   info@britcycle.com 

UK Breather Kit sales- email Paul Fotheringham at Shropshire Classic Motorcycles  info@triumphbonneville.com 

or call               0044(0) 1743 860146         0044(0) 1743 860146

EU and ROW Breather Kit Sales- email rexbunn@bigpond.com 

                                  Reports Index

100/Triumph- A Concours 3TA Installation

99/All Bikes- Warm Air Induction Breathing-The Next Step

98/ All Bikes- Dykes, The Father of Ring Flutter

96/The Ultimate Reference to Global Warming

94/ All Bikes-Useful Motorcycle Web Links

93/ Royal Enfield- NSW Electra Riders Wanted

92/ Royal Enfield- Flow Testing the Duckbill

91/ Harley-Davidson  New 2010 Sportster Kit User Guide

89/ Triumph- T20 Cub Installation

88/All Bikes DIY How to Blow-Test Engine Breather Unions

87/ROAD TEST-All Bikes- Why Never to Fit  PCV valves

86/ All Bikes- Do we Breathe to Air or Recycle Blow-by?

85/ Triumph- Bonnie Breathing- The Development History

84/ Royal Enfield-ROAD TEST-Bunn Breather Proving Trial

82/ Harley-Davidson-ROAD TEST-Power Gain & Bunn Kit

79/ DIY-Ten Tips on Breather Valve Placement

78/All Bikes-Blow-By (BB)- Causes and Cure- Part 1.

77/All Bikes How Does the Bunn Breather Kit Work?

76/ All BikesEthanol Fuels and Crankcase Breathing

75/ BSAThe Best A50 Research-Based Installation Sofar

74/ Cars-Breathing Air-Cooled Race Car Engines

72/ Classic Motorcycles- World Population of Surviving Bikes

71/ How Classic Motorcycles Boom When the Economy Busts

70/DIY Impact of Oiltank Froth on Crankcase Breathing 

69/ GALLERY: Reader Offer- Classic Motorcycling Book

68/ DIY ENGINE FEEDBACK via Temperature Sensing

67/All Bikes- Winterising Engine Crankcase Breathing

66/ Royal Enfield-23 Bullet FAQs

65/ DIY Motorcycle ‘Dehumidifier Kit’-User Guide

64/ All Bikes- Timed Breathers and Oil Venting

63/ BSA- The Best B33 Bunn Breather Sofar

62/ All Riders- Hydroxy (HHO) Valve-Warning Notice

61/ All Bikes-Decision Rules for Breather Placement

60/ All Bikes-Piston Ring Seal and Blow-By

59/ All Bikes-Rediscover “Draft-Tubes”-DIY Guide added

58/ All Bikes**How Engines Breathe on the Road**

57/ All Riders- Why Open Breathers S-U-C-K

55/ The 3 Top Problems in Crankcase Breathing R&D

54/ All Bikes- P-Trap Perils & Horseshoe Breather Block

52/ Old Bike Australasia Breathing Article 

51/ 2009 Bunn Breather Product Range Announcement

50/ All Bikes- DIY Clips & Fixings for  Breathers & Unions

49/ All Bikes DIY Connecting the Bunn Breather

48/ All Bikes- Altitude Effect & Crankcase Breathing

47/  BSA- Twin Installation with Bunn Breather

46 All Bikes- Stop Sumpwater, Dehumidify the Engine

45 All Bikes- Crankcase Breathing- Altitude Effect

44 Classics- Motorcycle Breather Icing

43 Norton-  Breathing the 650SS Norton Twin

42 Harley-Davidson- Breathing the 1340cc Shovel

41 Royal Enfield-  Reviewing Crankcase Research

40 Classics- Causes of Bad Breathing/Wet Sumping

39 All Bikes- A Note on Nitro and Methanol

35 Velocette-  Installation- A Creative Example

34 All Bikes- Thirteen Rules for Crankcase Tuning

33/ Triumph- One of the Best Bunn Installations

31/ Triumph and BSA-  Handy Breather Tip

30 GALLERY:Norton Pristine Commando & Bunn

29 Suzuki-  GSX1400 Breathing with a Bunn

28 GALLERY: Triumph Bunn Breather on Unit Single

27 All Bikes- Where To Put Your Bunn Unions?

26 All Bikes- a Review of Breather Valves

25 BSA-  Unit Singles breathing with a Bunn

24 All Bikes- Sumpwater and How to Get Rid of It

23 Harley-Davidson-Power Increase & Bunn Breather

22 Harley-Davidson  Breathing the Evolution Engine

21  VW- Solving Boxer Breathing with Bunn Breather

20 GALLERY: Yamaha- Bunn Kit & Yamaha 1100

19 GALLERY:Norton- Commando with Bunn

18 GALLERY:Triumph Twin Pics with Bunn Breather

17 GALLERY:Royal Enfield- Curing Blow-By

16 GALLERY:Vincent- Bunn Blow-by in a Vincent

15 All Bikes- What's Coming Out of Your Breather?

14 Harley-Davidson-MkIII Breather for Evo Sportster

13 GALLERY:Harley- 2008 Sportster Installation

12 GALLERY:Royal Enfield- Breather Installations

11 Triumph- TOMCC Book Review in Nacelle

10 Royal Enfield- 2008 MkIII Royal Enfield Breather

9 2008 MkIII Bunn Breather Kits Range-deleted 8/09

8 All Bikes-Why Car Brake Valves Don't Suit Breathers

7 First USA Book Review out this week!

6 GALLERY:Vincent-  Dyno Trials 2006-2007

5 Steve Wilson Review in Real Classic

4 Another Great Review from VMX magazine!

3 MotoringMarketplace Book Review NZ-Deleted 8/09

2 First Oz review by Mick Matheson in AMCN

1 Classic Motorcycling: A Guide for the 21st Century

 Manufacturers today supply bikes with the crankcase connecting to the air intake, either directly or via a valve. Some of the blow-by vapour will (hopefully) be sucked into the engine air intake tract. For $1 worth of tube, you gain EPA compliance, which is a lot cheaper than designing and manufacturing a real crankcase breather. This must seem a bargain for manufacturers…but is it ideal for the rider? 

Apparently not, as many riders purchase a range of aftermarket breathers, trying to improve crankcase ventilation. Many of these alternatives redirect blow-by vapour to atmosphere. The question arises, does this change have any effect on carburation and if so, is any tuning required after effecting this change?  

To answer this, we first examine the composition of blow-by. This is tricky as blow-by composition varies by rpm, load, oil viscosity and temperature, as well as where the gas is sampled in the engine. Also we need to look at the gases and their condensates to get the whole picture. As “blow-by = combustion gas + unburned fuel mixture”, let’s start with ordinary exhaust gases. These comprise 72% Nitrogen, 14% CO2, 13% water and 1% acids, soot, nitrogen & hydrocarbons (Hillier 2006).

 Research by Murikami et al 1991, shows NOx, CO and CO₂ levels are similar for exhaust and blow-by gas, while other constituents vary.  By sampling blow-by under piston rings and condensing it, he gives us a first comprehensive picture of blow-by, as it’s produced in an engine under a range of loads. The blow-by condensate forms an acidic black fluid, settling into unburned fuel and water layers, later casting a gray sediment. This is all bad news, particularly as deposition of sludge blocks oil-ways, scours bearings and corrodes metals. 

At idle, blow-by composition is: 67% oil, 22% fuel, 10% water and <1% solids by weight.At wide open throttle (WOT) in the test engine, this changed to: 58% oil, 30% fuel, 12% water and <1% solids. By comparison, in the engine oil at the same time, unburned fuel was only 1-3% and water 0.2% (the latter agrees with our research into moisture in engine oils.) 

Some key points can be drawn from this and later research by Moritani 2004.

1/ Blow-by vapour and engine oil droplets in the crankcase form two ‘phases’ in the stream of vapour venting the crankcase. This explains why oil figures strongly in Moritani’s figures. More or less oil is carried out the breather, depending on crankcase conditions.

2/ Of the non-oil phase, unburned fuel comprises 68-71%, and is mainly aromatic hydrocarbons, some 42% at idle rising to 67% at WOT.

3/ The remainder is largely water 28-31% at WOT, containing NO₂/NO₃/SO₄.

4/ The water fraction has an acid ph of 4.6 down to 3.85 at WOT, roughly that of red wine.

5/ Air-cooled bike engines run at high temperatures and as the crankcase warms, unburnt fuel is vapourised from the engine oil, to join the blow-by gas.

6/ Under load, the unburnt fuel fraction in blowby condensate increases by 50% to roughly 1/3 by weight. (The unburnt fuel composition is denatured as fractions that vapourise at lower temperatures are purged first; much like a distillation column.)

7/ The blow-by sampling device, was in effect an engine breather. Interestingly it reduced the blow-by gas entering the crankcase by 48%, showing how effective simple engine breathers can be, even if only 2mm diameter as in this case. (Our research supports this).

8/ Oil, ring and piston wear drop as rpm increases. This is due to less oil around the rings at low revs…an argument to keep above 3000rpm, and ensure your oil pump is sound! 

Two further points arise…firstly aromatics are concentrated in the unburned fuel fraction of blow-by, and these may affect octane rating. Aromatics also increase engine deposits, something to avoid. Secondly, fuel blow-by isn’t confined to the combustion stroke, for fuel enters the crankcase on every stroke.  

This is why fuel is the most part of blow-by…for it follows two pathways into the crankcase, to become the major constituent of blowby gas. First, on the induction and compression strokes, it dilutes the oil around the piston, and flows down the barrel.  Then during combustion and exhaust strokes, it is forced past the rings into the crankcase, along with a fraction of combustion gas. There is always unburnt fuel in combustion gas as bike engines run at less than the “ideal” air/fuel or stoichiometric ratio of 14.7:1, at which point all fuel is burnt. Bikes run at 12-13:1 i.e. a little richer. This helps stabilise engine temperature and avoid detonation, at the expense of boosting blow-by.  

 So where does this leave our question on weak vs rich? The evidence suggests blow-by gas, if introduced in sufficient quantity to the inlet tract, could add a mixture rich in aromatic hydrocarbons and water vapour. The joint effect of this would be to enrich the mixture and increase its octane rating. As well, ‘water injection’ may help avoid detonation, while lowering combustion temperatures and increasing power, as pioneered by fighter aircraft in WWII.

 Is blow-by then in fact something we should prize? The positive aspects of blow-by are attractive i.e. potentially higher octane fuel plus more power and protection from detonation. On the downside are increased engine deposits.  

Perhaps unfortunately, the deal is not open, for two reasons:

First, the quantities of blow-by available are insufficient to make any difference. On motorcycles, blow-by volumes are 5-10 litres per minute. This equates to 2% at idle (down to 0.4% at speed); of airflow through the combustion chamber. It’s only exceeded in engines with advanced wear and racing engines exhibiting ring flutter at WOT. Motorcycle tuners reckon a 10% change in a tuning variable, is about the minimum change you can detect. At less than 1%, there simply isn’t enough blow-by to detect a mixture difference, except possibly at idle. 

Second, the major part of blowby gas is oily vapour. Passing this into our engine and burning it will definitely cause engine deposits and soot.   

Some riders reckon they’ve  experienced improved power when removing crankcase breathers that go into the air inlet, due to leaning out the slightly rich mixture (as it goes towards stoichiometric ratio).  In theory, this would not be good for engines running lean already. In practice, any power increase with improved breathing has more to do with improved crankcase pressure/flow; than an altered fuel mixture.  

The original question seems to be answered. Recycling blow-by into an engine air intake will richen the mixture, and redirecting blow-by to air will weaken the mixture. However the quantities involved are so small, that no observable difference will be seen. On the other hand, passing blow-by to atmosphere avoids re-feeding oil into your engine; oil that will burn to form soot and carbon deposits that one day will need to be scraped out. 

On balance it’s advisable, from the point of view of engine health, to vent blow-by to atmosphere. Oh and as well, no tuning is required.  

KT’s extremely fine restoration of this 1958 Triumph 3TA is evident in the pics. He reports “the bike was a “deceased estate”, and last ridden in 1970.  It looked pretty sad, and was definitely a candidate for a complete nut’n-bolt  restoration when I bought it in 2007.  However, other than missing engine torque stays it was complete, and hadn’t been butchered, so was a long drawn out but satisfying restoration.”

KT opted for a “Top>>Down” Kit installation, “as it was easier to “hide” the filter behind the rear covers (bathtub).  I went “in” through the rocker inspection cap and out through the existing breather pipe, having removed the butterfly valve at the rear of the inlet camshaft.”

A very tidy job and note the effective use of double-ear clips.

"The bike has now covered around 250 miles following completion, and as yet there have been no engine oil leaks, so presumably it is doing its job.  Even those notoriously leaky push rod tubes are completely oil free!  The only question I have is that, in addition to the usual Triumph “clatter”, there is a surprising amount of noise (clatter) from one or both of the breather valves…Thank you for what appears to be a very effective product.”

The valve noise KT refers to appears at idle on some bikes only, when tiny sound waves from the valve reach the air filter. It normally disappears above idle, and can be relieved by repositioning the inlet assembly, shortening tube length etc. The next generation of Kits will operate silently on every bike at all rpm (RB).   

  Many riders are familiar with “cold air induction”, in car engines. The fashion for pod air filters on bikes can be seen similarly. Cold air is more dense and contains more oxygen that hot air. Feeding cold air to the carburettor gives more oxygen to burn and more power. It’s the reverse effect of altitude on power. Engines in high places develop less power than at sea level, as air is “thin” and less oxygen enters the combustion chamber per stroke.

 In motorcycle crankcase breathing, “cold air induction” is unhelpful.  Our research shows “warm air induction” is preferable for breathing the crankcase. This report explains why, and some ways riders can achieve “warm air induction”. 

By way of background, our Bunn breathing technology establishes a unidirectional air flow through engine compartments, using pairs of opposed valves. The flow rates of the valves are designed to achieve a crankcase vacuum plus airflow through the engine. This makes us unique. We flush the crankcase with fresh air once or twice a minute, and so purge blow-by vapour, moisture and the sumpwater caused by ethanol fuels.

 There is normally a temperature gradient between sump air and open air, depending on the season. Much riding is on sunny days when ambient temperatures range from say 10C in the UK to 40C in Australia. Now imagine the air temperature inside the sump is 50C, and we pass 5L/m of air through the engine. When the air outside is 40C there is a 10C gradient between sump and atmosphere. When the outside temperature is 10C, there is a 40C gradient. This gradient is important for crankcase breathing. 

The gas laws tell us two things about this. First,  the volume of a gas varies with temperature. As temperature goes up, the gas takes up more space i.e. it’s volume increases.  Second, this change is more pronounced at lower temperatures. 

Here’s a crankcase example:- Say your British twin has a crankcase of 5 litres. Say we pass 5L/m of fresh air though it. The fresh air expands as it mixes with hot blow-by vapour and warm air in the sump and rockerboxes. How much it expands depends on the temperature gradient inside to outside. On say a nippy British morning at 10C, there’s a 40C gradient, while on a Sydney summer run, it may be as little as 10-20C.  The Gas Laws show us our 5L of fresh air at 10C in the UK can expand to 25L if heated to 50C. On the other hand, our 5L of air at 40C expands to only 6.25L at 50C.

 As well, air pressure in the crankcase can increase along with the increased volume of cold air, with adverse joint effects on engine breathing. Inducting warm air limits expansion and the pressure increase, in this case to less than a quarter.  Riders should not unduly worry, as these figures aren’t seen in regular riding. Engine operation, blow-by and the Bunn Exhaust breather deal with these  effects.  Still, it seems clear “cold air induction” does not help our quest to optimise engine breathing, especially in cold weather riding. In cold weather, “warm air injection” makes most sense, for cold air expands more when heated.

The two key findings from the above are:-

1/ Cold air expands when injected into the hot sump.

2/ Warm air expands less when injected into a hot sump.  

Whether in Sydney or London, we can help our engines breathe using “warm air induction”. This minimises air expansion in the crankcase and potential pressure change. To obtain warm air induction, we position our Bunn Inlet assembly to collect warm air. This positioning will vary by the aerodynamic styling of the bike. For simplicity let’s discuss a naked bike. The places  to collect warm air lie close to the engine, barrels or crankcases, and behind oil-coolers, radiators and rockerboxes. Moreover we should keep close to the mid-line of the bike, where we are inside the boundary layer and air pressures are highest. We avoid placing our Bunn Inlet assembly where it’s exposed to the air-stream over or under the bike. It should be in a sheltered spot where air is relatively warm and still.

Positions to consider are:  behind a cylinder, gearbox, or crankcase: above the engine, say up under the tank: or close (but not too close) to an exhaust pipe, say up in the gusset on British bikes. By placing the Bunn Inlet assembly in an ideal location, we optimise the breathing system, helping it achieve the best possible air pressure and air flow through the engine. Our 2010 Kits (undergoing final road-trials) are designed to exploit ‘warm air induction’.

One of the forgotten classic motorcycle heroes is Paul de Kantzow Dykes, now vaguely associated by a few old hands, with Dykes piston rings. He was much more than this. He was a British aristocrat, academic, engineer, inventor, lecturer and soldier. He lectured at Cambridge  before WWII, where he served as a Major in the Royal Artillery. He resumed lecturing in engineering at Kings College, until 1972. I’m sure his lectures were lively.

 He was also public-spirited, assigning his patent rights to MIRA, by which all classic motorcyclists benefit. Unfortunately few of his writings survive in the public domain, and he doesn’t appear to have had time to write a book. Nevertheless, he was an original thinker and his experiments and technologies make very good sense today. I wish I’d met him for a chat.

He seems to be first to identify the phenomenon we know as “ring flutter” and to map out its causes and measures to overcome it. Ricardo for example, has little to say about breathing and blow-by and nothing on ring-flutter. Dykes several patents show a lively, inventive mind together with a strong commercial interest . He focused his commercialisation efforts on the USA, where his ideas were soon taken up and copied. Today, his path-breaking work is relevant to all riders, especially those seeking performance.

Ring-flutter is to many riders an unfamiliar term. It can simply be described as a loss of seal between the piston rings, especially the top ring; and the piston land and barrel wall. This occurs predictably  under certain conditions of engine design, speed and load, much as Dykes mapped out for us over 1948-1952, by extended experiments on lab engines. One result of ring-flutter is a swift increase in crankcase air pressure and oil venting the breather, coupled with a loss of barrel lubrication and an increased chance of the piston nipping-up.

The good news for todays riders is that, given key indicators of engine design i.e. conrod length, stroke, ring width and rpm…we can predict the onset of ring-flutter, and do something to prevent it. Dykes tried to prevent it, via a range of piston ring designs. The most commercially successful of these were his patented “L” ring designs. These addressed the causes of ring-flutter with some success, though they seem to have fallen out of fashion. Still it’s a very valid design solution to ring-flutter and associated blow-by.  When riders report oil venting their breather, I often follow Dykes path and calculate the chances of ring-flutter being the culprit.

  “By way of general comment, Harley-Davidson switched to a kind of Bottom>>Up breathing around 1986.  Since then all Sportsters and touring models use this breather flow….so although Harley-Davidson don’t use my breathing technology, exhausting blow-by out the rockerboxes, via the pushrod tubes,  and against the return oil flow; has strong support. 

With Meriden Triumph twins, we’ve had good results breathing Bottom>>Up, as with nearly all British and USA engines. Still I recommend riders perform a “Blow-Test” prior to installing any breather system, to demonstrate a clear airway between the selected inlet and exhaust unions.  You ask what I think about breathing Bottom>>Up and the risk “… that venting from the rockers can restrict the flow of oil on its natural path down to the cams?...” Here are my thoughts, with special reference to the Turner engine. 

1/ It’s always wise to start with the lubrication system when considering crankcase breathing. The Triumph rockerboxes are lubricated by a tap in the oil scavenge line. This supply varies by engine rpm and other factors e.g. how dry the sump, oil viscosity and temperature. A varying % of the oil return is diverted to the rockers. If say, at 2,500rpm a Triumph oil pump in good repair is pumping 0.4-0.8 litre (quart) per minute {L/m} on it’s feed side, and roughly twice that on  it’s scavenge side, then roughly 30-50% or  0.2-0.4L/m may be reaching the rockers. A little will pass down the valve guides and a little may be lost elsewhere, but 0.3L/m is probably a fair oil return from rockers to sump.

 2/ The oil return side is aerated, depending on conditions in the sump. Thus Triumph rockerboxes are normally fed aerated oil. Unless the boxes are vented, this air must exit the engine via the crankcase i.e. it must pass down the pushrod tunnels. Edward Turner designed it that way, proving air can safely pass down the pushrod tunnels, together with oil flow.

3/ Turner drilled the pushrod tappet blocks to allow oil and air to flow down. In my experience, these drillings are adequate to allow air and oil to pass in either direction. 

4/ With a Bunn Breather, crankcase air volume, pressure and flow are all reduced. This means relatively smaller volumes of blow-by gas (5-10L/m) pass up the pushrod tunnels compared to say on open rockerbox vent.

 5/ Crankcase blow-by gas flow and oil scavenge flow are inversely related. At low engine rpm, oil feed to the rockers is minimal, perhaps 0-0.02L/m, and rising with engine rpm. Blow-by gas is at a peak at idle, and falling as engine rpm rises. Their interplay minimises the chance of flow interference in the pushrod tunnels, over the rpm range, with one of my Kits.

 6/ The oil and gas flows are moving in opposite directions around the pushrods. However in practice the oil flow down the pushrods is intermittent, given pump-flow variations, entrained air, tidal movements in the rockerbox oil during acceleration, braking and cornering. Thus there is plenty of room for small airflows to move up the tubes.

 7/ A “Blow-Test” demonstrates the quite surprising capacity of the Triumph pushrod tunnels to pass blow-by gas and oil.

 8/ Breathing Bottom>>Up has been an option up to now. However with the increased  sumpwater happening with ethanol fuels, it’s becoming a necessity. The logic is: as we have more moisture accumulating in our crankcases, and as water vapour naturally  rises, we can better purge moisture with the unidirectional airflow flow of a Bunn Breather if we exhaust moisture from the top of the engine. 

9/ Pushrods continuously move up and down in their tubes. Half the time they move against the oil return flow, without any obvious interference with oil return. Compared to this activity in the pushrod tubes, the small rising airflow appears of little consequence. 

 10/ With factory timed breathing, the crankcase spends a lot of the cycle at increased air pressure. While the pressure in all connected  compartments quickly equilibrates, there can be times when the rockerboxes lag behind, and are at a lower pressure than the sump. Now this pressure differential may interfere with oil return (with factory breathing). I have no evidence either way.  

This is the first (and last) non-breathing report on this site. I accepted Global Warming until I read this new book... ..."Heaven+Earth"

A neighbour loaned me this ultimate answer to the Global Warming {GW} question. It's a new book by Australias leading geologist Prof Ian Plimer..."Heaven+Earth" published in May 2009 by Connorcourt Publishing. The first printing sold out in 4 weeks. If you really want to get to the bottom of this matter, this is it.

It's a 500 page book ( with 2311 references). It is however, written simply and entertainingly for everyman. It dissects the science behind GW. It shows the science is biassed and selective, and the  fundamental assertions by the GW lobby are unsupported, indeed contradicted by the planets geological record.

 I thought Plimer was very close to libelling the GW lobby, including Mann et al,  till I recalled the defence against libel... is the truth. Plimer speaks the truth. I was prepared to accept GW till I read this book. Now I understand it is just bad science, worse in fact than the Cold Fusion scandal of twenty years ago.

As discussed elsewhere on this Blog, many classic bikes wet-sumped when new and many still do today. Some brands of today’s bikes e.g. Royal Enfield and Harley-Davidson, are also prone to this.  Many riders think of fitting an in-line oil tap in the feed line, to prevent this. Many are deterred by the consequences of forgetting to open the tap before talking off i.e. a seized engine and an expensive repair bill.  

In my 2007 book Rollo Turner and I  devised a mechanical safeguard  to overcome the problem. This however was not an off-the-shelf item. Later I invented a more user-friendly electro-mechanical device, one that can be easily assembled by any rider, from over-the-counter components.  The pic below shows the components and finished product.  

 The DIY “Oil Tap Warning Kit”,  is made up of the following components- 

1/ A ¼” BSP Ball valve-rated for oils.

2/ A small magnetic switch, of the type used in home burglar alarms

3/ A small round, rare earth magnet

4/ 1/8" BSP thread brass fitting to enable hose fixing to valve.

5/ Piece of double-sided tape

6/ Short piece of wire (optional) 

These items are variously obtainable from plumbing, hardware and engineering supply retailers and electronics stores, al least in Australia.  

Assembly

1/ Fix the magnetic switch to the valve body with tape, as shown.

2/ Fix the magnet inside the hollow valve handle with e.g. hot-glue gun or sealant.

3/ Optionally, lockwire the switch to the valve. That’s the assembly completed. 

Installation

1/ Locate the oil feed line, below the oil tank, where you can see and operate the oil valve.

2/ Cut the line and insert the oil valve, securing the valve with hoseclips.

3/ Wire in the switch to e.g. a warning light circuit. On my BSA B44, I have a spare warning light in the headlight, so I connect the switch to this.    That completes the installation 

Operation

1/ Close valve after switching off from your last ride. This stops oil feed to your engine!

2/ Before starting the engine, ENSURE you ALWAYS open the valve.

      WARNING- If you fail to do this even once, the engine will seize!

3/ The Kit will help you to remember by showing an “oil-on” warning light, or turning on whatever other warning device you chose to wire in.

4/ The operation is simple. When the valve is opened, the handle swings against the valve body. The magnet inside the handle operates the magnetic switch. This closes the circuit, and your oil-on warning lamp  lights up.

5/ When you close the valve, the handle moves the magnet away from the switch, the circuit goes open, and your oil-on warning light goes out. Simple.

6/ The switch I use is “normally open” so when the oil valve is opened, your warning circuit goes closed and the indicator goes on. No warning light = no start-up.

7/ When you change oil, ensure the valve is open, and prime your oil feed line if needed on some bikes.  

Disclaimer:- I make no warranty as to the performance of this device. Riders use it at their own risk. The device won’t help remind you UNLESS you scan your engine warning lights BEFORE starting up. It is not a perfect solution, but it’s the best I’ve ever seen.  Copyright © A.R.Bunn 2009

Here are web links to useful motorcycle sites around the world. This list will extend over time:-

1/ http://www.classic-motorbikes.net  -Classic Bikes

2/ http://www.motorbike-breakers.com  - Motorbike Breakers

3/ http://www.motorcycle-parts-accessories.co.uk  - Motorcycle Parts   

4/ http://www.motorcycle-sites.co.uk  - Motorcycle Website Design

5/ http://www.motorbike-search-engine.co.uk  - Motorcycle News

6/ http://www.tunemyengine.com  -Remapping Specialists 

7/ http://www.panther-publishing.com - The Classic Bike Book Publisher

8/www.motorcyclesupermarket.com -The New UK Bike Shopping Site

* WANTED*  Five (5) Royal Enfield Electra  Riders for the  Second Electra Crankcase Breathing Trial 

Volunteers are sought for development road-testing of the next generation of Bunn crankcase breathers for the Royal Enfield Electra motorcycles. The first road trial was held by Royal Enfield Australia and Carlel in the UK and Australia in 2007. This first independent public trial proved the performance  of the new Bunn Kits for Classic, de Luxe and Electra models.   

Now three years later, Electras are reaching higher mileages and being performance modified. They run with increasing engine wear and tear. On some bikes this leads to impaired breathing performance, whatever their breather type. After four more years studying this engine, I recently made another breakthrough in its behaviour. Solving this lead to a new generation of  Bunn Breather Kits. It is these Kits we will be road-testing.

 As in 2007 I believe such innovations should be independently  trialed. Riders wishing to read the 2007 Trial Report can find it at  http://bunnbreather.bigblog.com.au/post.do?id=350622   or go to   http://bunnbreather.bigblog.com.au and read report number 84/. We will follow a similar trial approach this year. 

Eligible bikes -  include  any model year of Royal Enfield Electra 500cc solo motorcycle.  High mileage bikes are welcome.  2/5 places are reserved for performance-modified bikes i.e. those with big-bore kits, high compression pistons etc. The only bikes ineligible are non-runners, basket cases and those with such ring and barrel wear... they need immediate re-boring. Bikes with oil leaks, oil dumping, elephant snot and bad crankcase breathing are especially invited.  

Trial Requirements- Entrants will need to ride their Electras to my Castle Hill, Sydney workshop before Christmas, for engine testing and breather installation. Riders will need to make two or three test runs with the breather, of 50-100kms plus.  Riders will report by phone or email on their road test experience and observations on their crankcase breathing. A simple report sheet will make this easy. Riders interested in joining the trial should email Rex Bunn on rexbunn@bigpond.com   as soon as reading this invitation. It’s first come, first served. Apart from performing a public service for the Electra community, triallists will be given a complimentary Bunn Breather Kit as an honorarium and a copy of the Trial Report.  Riders names will be held confidential as in 2007.

UPDATE:- This trial is postponed, as we are in NZ for the summer classic racing & rallying season.

Published test data on these duckbill valves are rare, so as part of our new Electra Kit R&D, I made up a test rig. For riders unfamiliar with duckbills, they’re like mitral valves in human hearts. Their shape (like a bishops mitre, a duck or platypus beak), is  designed to open under pressure and stop back-flow. They’re used in industry, often with fluids in e.g. boat bilges. They’re  known to perform  poorly in low-pressure, back-flow applications. Here are the test findings.

Item tested- Poineer duckbill 200mm, 8mm ID, valve 3mm by 0.63mm.

Test Protocol- As with Harley valves, a test rig was devised  to measure flow and back-flow, cracking pressure, peak flows and ability to cope with soot particle buildup.  Comparison flow tests were made with a Bunn valve. Valves were taken from engines in service. [NB:duckbills are used singly vs Bunn valves in  arrays. Bunn flow tests test the valve only, not breathing]

Findings

1.0 Flows- The ability to flow gas is one of two acid tests  for crankcase breather valves. Both valves achieved  satisfactory flows  across the standard breathing range i.e. 0-15 L/m.

Duckbill- The Duckbill passes <5L/m without change in pressure gradient across the valve.  From 5-15L/m, pressure builds across the valve  to 10-30mmHg.  This is sufficient to cause oil leaks.  The duckbill fails this test.

Bunn- The Bunn valve passes up to 15L/m without increase in pressure.  They operate the crankcase at lower pressure than Duckbills. This valve passes testing.

2.0 Backflow- the other acid test is how well a non-return valve prevents air flowing back past its seal.

Duckbill- This valve allowed <7L/m backflow. The backflow cracking pressure is 5-10mmHg The backflow varied over successive trials, showing the duckbill has poor, variable sealing. This is a known weakness of the design, with gases flowing at low pressures as in motorcycle crankcase blow-by. On this score the Duckbill fails. Its performance is similar to an open tube.

Bunn- This valve prevented backflow. It passes the test.

3.0 Cracking Pressure- This measures valve sensitivity to pressure change.

Duckbill- The resting state of a duckbill is ‘normally open’. From 0-5 L/m flow the valve doesn’t shift.  It acts as an open tube. At 5-10 L/m pressure builds across the valve, and the mitre opens. The 'cracking pressure' is 10mmHg.

Variable performance means every stroke can give a different result. No consistent crankcase breathing can be achieved  with this valve. 

Bunn- This valve cracks at 1/20th of the Duckbill. By this test the Bunn valve is preferable  for crankcase breathing.

4.0 Fouling and Cleaning-  The Duckbill bore can be inspected. The seal can be cleaned with a cotton bud, but this may score seal surfaces.  Given the backflow, road dirt is sucked into the valve and builds on the tiny 1.9 sq. mm seal area, as shown above. Heavy breather flow may wash some dirt out, giving intermittent blockage. Riders should inspect and clean these valves.

5.0 Conclusions

5.1 Both valves pass sufficient air to breathe a 500cc engine.

5.2 The duckbill is unable to pass >5L/m without  pressure developing. The Bunn valve does not have this problem.

5.3 The duckbill allowed back-flow of <7L/m. This is no surprise given its  design and the flows and  pressures in crankcases. The duckbill does not  act as a non-return valve here. As a result, it’s unsuited for this application.

5.4 The duckbill cracking pressure of 10mmHg is too high for effective crankcase breathing.

5.5 The seal failure allows duckbills to suck up unfiltered  air into the engine. This is a serious issue, as road grime stops this valve sealing.  As well, sucking road dirt into the crankcase is unacceptable.

5.6 On Enfields these duckbills are found in dirty spots e.g. over the rear chain. Here they receive a lot of oily debris flung off the chain harming the sealing. I suggest riders only use duckbills in clean locations, if they use them at all. There are simply better valves available than this type.

From today we introduce the new series of "Tri-Breather Kits" for the Harley-Davidson Evolution Sportster engine family.

These new Kits incorporate three breather asemblies to better breathe the engine. The new mini-filter asembly enables "warm-air induction" to the cam gear case. The draft tube assembly further lowers crankcase pressure. The oil tank breather assembly prevents pressurising of the oil tank.

The photo series below shows the  breathers' installation and connections. Tubes are colour-coded thus:- Red for oil tank breather, Green for warm-air induction, and Yellow for blow-by exhaust. 

First, a photo showing the three breathers:

Second, the Inlet breather assembly. This is currently shipped "low position"

Third, the Exhaust breather asembly and Draft Tube.

Lastly, an Inlet assembly using the "rear barrel' position, for optimal warm air collection.

After labouring for a decade in this neglected section of motorcycle engineering, I see why riders overlook it’s importance.  Roy Bacon said it best...

 “This is an area that often gives owners a headache...as much of the system consists simply of holes and these cannot...appear on a parts list” (BSA Singles Restoration 1988, p103) 

This is perhaps why breathing looks irrelevant to some riders...till they have a problem. Bacon’s also clear on this...

 ” On all engines...good breathing is as important as good joints in cutting out oil leaks... including all the holes within the engine that contribute to the system” 

I agree. The difference between success and failure with oil leaks, can be a subtle difference in a hole, valve or breather tube, or even how the tube or valve is positioned. As in bike tuning generally, there is no alternative to research by ‘trial and error”. There is no general theory to guide us. The  theory we need lies in the Navier-Stokes equations, and these have been waiting 150 years to be solved.

A $US1,000,000 prize awaits the first person to unlock them. If/when  it happens, we will finally understand what goes on inside crankcases. See this link for details on this fascinating puzzle... http://agutie.homestead.com/FILEs/world_news_map/navier_stokes_fluid.htm  Until then, we continue researching this field, seeking practical ways of helping old and new bike engines breathe better.

This very tidy concours Triumph Cub in NZ had a few oil leaks, signs of crankcase over-pressure. The owner tried a couple of breather installation options before settling on the one shown. This is a Bottom>Up approach  using the OEM timing case union, plus a new rocker-box hatch union. The bike road-tests well with the oil leaks reducing nicely.

 With traditional crankcase breathing i.e. using an exhaust-only breather; it was simple to know if your breather connected to the sump...we just listened or watched  for the ‘sucking and blowing’ activity, and the oil coming out! 

With the advent of Bunn technology, riders can choose how to breathe their engine, using a variety of breather unions on various parts of the engine.

Given we now pass unidirectional air-flow through the engine, it’s useful to consider which way you want the air to flow, and which breather tube will purge blow-by vapour from your engine. A Blow-Test is invaluable for this.

 A “Blow-Test” is very simple. Here’s a ’Five Step Guide’ on how to do one: 

1/ Check Blog reports 27/ and 61/  for advice on where to place unions.

2/ With engine off, select any two unions you’re thinking of using.

3/ Fix some scrap tube to the two unions, drillings or holes you may want    to use. Tape the tubes in place if necessary, with gaffer tape.

 4/ Blow  firmly in one tube and rest the other in your ear or to your face.

5/ If you feel air on your face, there’s an airway between the two unions.     Effective breathing can take place between these unions.  

Test Tips:-* Air should pass freely between the two unions.

* If airflow is absent or feels restricted, consider another union position.

* A long breath normally fills the crankcase, and some air will flow back.

* Ensure you’re not trying to use a drilling used by the lubrication system, e.g. an oil pressure switch, oil bypass valve, oil non-return valve etc.

* The unions need to be above operating oil levels in sump and timing case. Otherwise no air can pass.

* Some oil pathways also connect engine compartments i.e. pushrod tubes, cam-chain tunnels etc. These can usually be used for breathing.

* If in doubt, refer to your Parts or Shop Manuals for the oil diagram. 

Copyright © A.R.Bunn 2009

Background:- This report publishes test evidence on PCV valves with  air-cooled, four-stroke bike engines. Its surprising to find otherwise  savvy riders fitting car PCV valves to their bike breather. Why do they? There is no evidence car PCV valves help breathe the motorcycle crankcase. 

The evidence shows they fail to assist crankcase breathing on nearly every classic and modern motorcycle. The only possible exceptions to this are bikes recycling blow-by, and some triples. The other 95% of bikes which should never use a PCV valve include nearly all classic Triumphs, BSAs, Nortons and all  British Vee and parallel twins, boxers and singles.  Also excluded are all vintage bikes, and Harley-Davidsons and modern bikes with aftermarket air filter assemblies. No bike with ‘open breathing’ i.e. that breathes to air irrespective of age; should fit a PCV valve.

The trap ensnaring  these riders seems one of sheer faith, i.e. that as  PCV valves are used on cars, they might work on bikes. Also you can buy a used PCV from a wrecker for $5, or $20-$40 new.  As well, the urban myth about PCV valves is on many bike forums, where riders call just about any valve a PCV valve. Many riders don’t understand a PCV valve or how it works on a car or bike. Few riders test valves they’ve installed, so cannot say if they work or not. Thus the myth perpetuates and oil leaks continue.

While I’ve tested PCV valves along with just about every kind of valve imaginable, and criticised PCVs  in articles and lectures; I’ve not published evidence on this Blog, till now. If you use a PCV valve or have a friend who does, this report is for you.

While many riders buy used PCV valves, a fair test called for a new PCV valve. I bought a new US-made Fuelmiser brand  PCV valve, for $12.98.

The test procedure I made up called for bench and road testing and used my current test vehicle a Harley-Davidson Sportster. The bench tests measured usual variables i.e. cracking pressure(s), air flows, valve orientation, sealing, back-flow and valve oscillation.

Design Issues-

 PCV valves fail to function on bikes on the bases of design, seal weight, valve inertia, cycling speed, pressure and flow range, servicing and installation. In fact it’s hard to find one thing PCVs actually do well on a bike engine. When we compare the engines for which they’re designed, the reasons for this become clear.

Engine Design-

 Car PCV valves are designed to operate in multi-cylinder, water-cooled, big wet-sump engines with no air displacement. Motorcycle engines have fewer cylinders, small dry sumps, are air-cooled, with lots of air displacement. From the crankcase breathing point of view, about the only thing car and bike engines have in common, is they’re four-stroke Otto engines. 

Valve Operation-

 Car PCV valves are designed for, or powered (if you like), by the smoothly-changing intake manifold vacuum. On a motorcycle breather they face crankcase pumping action, i.e. high pressure, vicious pressure oscillations that displace air from the crankcase.

Valve Design- PCVs are designed for one purpose...to prevent blow-by escaping  to air. Any negative impact on engine function is a pity. PCVs are vacuum-operated, not high-pressure-operated. They face the sucking action of the intake manifold in a car. In a bike they face the oscillating wind under the pistons. A valve designed to respond to vacuum, responds differently to high-pressure flow. When we force air through the valve from underneath, vs sucking it through from above; the valve operates outside it’s design parameters: we should not be surprised if odd things happen as a result. 

All PCVs are ‘metering’ valves i.e. they let more or less air past, depending on the upstream vacuum. They are not ‘non-return’ valves. They allow some air to pass in both directions (making  them useless for bike breathing).  They have secondary functions as a flame barrier and a flow-restrictor. The first is handy on a bike, the second a hindrance.

PCVs are designed to restrict flow at low speeds and open wide at high speeds. This avoids choking car engines with blow-by at low speeds. At higher speeds, car engines can digest more blow-by so the PCV opens wide.

This does not marry at all with bike engines. These pass most blow-by at idle and low speeds. Blow-by reduces as bike speed increases. We need valves that pass maximum blow-by at low speeds. This is the opposite  of car engines, which are covered at http://www.autoshop101.com/forms/h63.pdf

Bike breather valves need to oscillate in time with the engine beat. Car PCV valves do not, for the engine beat is absorbed by adjacent barrels and the big sump air space. PCVs are not designed to oscillate at high speeds, as required on bikes. The moving parts are far too heavy. See Blog article 26/ below for specifications of breather valves.

Test Findings- The test results for this PCV valve are similar to  results from other PCV valves over the years. 

The PCV restricts flow at low engine speeds. This increases crankcase air  pressure to 765-775mmHg over-pressure at the normal range of bike crankcase flows i.e. up to 5-10L/m. The higher flow, second-stage PCV opens at these higher pressures allowing more air through. Unfortunately bikes require valves that pass max flow at low speeds, the opposite to PCV flow. This is a second  root-cause of their uselessness on bikes.

2.0 Air Flows- PCVs have two states  (for low and high vacuum). When we apply pressure flow...at low-flows the PCV passes 0-7 L/m. At high flows, it passes 7-28L/m. Ironically the low-flow stage suits bike engine flows at cruising speeds and the high-flow stage suits bikes at low speeds. However the resting state of a PCV is low-flow, so PCVs are incapable of meeting bike engine demands. This is a third root cause.

3.0 Back-Flow- A PCV is only designed to stop flames in the event of a back-fire. It is not designed as a non-return valve, as required on bike engines. Testing showed this valve passed up to 2.4L/m at the low-flow stage and up to 4.7L/m when the high flow stage opened. This flow range covers the normal bike breathing range, hence allows the engine to breathe openly. Pressure spikes and oil leaks etc go uncorrected. This is a fourth root cause.

4.0  Valve Orientation- Like others, this PCV valve is designed for upright positioning. This is fine on a car, but what happens when you corner a bike with a PCV valve? As the PCV tilts, its cracking and flow changes. At 0-30 degrees tilt there is low-flow, as the pintle moves off it’s seat. By 30 degrees the first stage opens, and at relatively low flow. Near 90 degrees, the second stage opens again at relatively low flows, and allows two way air flow, as the pintle binds against the casing. This means the PCV passes air both ways unless it’s vertical. It really doesn’t act like a valve at all. If the PCV is inverted, it takes a flow of 45L/m to crack the pintle. No motorcycle I ever tested came close to generating a flow like this. This is a fifth root cause.

5.0 Sealing- The first requirement of a motorcycle non-return breather valve is that it seals. PCV valves are not designed to seal. This is a sixth root cause.

6.0 Valve Oscillation- From the above it’s clear PCV valves are not designed and are incapable of handling bike crankcase pumping by oscillating in time with the engine. It’s outside their design. This is a seventh root cause.

Conclusion- PCV valves join the group of valves below; as tested and rejected for use on motorcycles. PCV valves cost $12-$40 each, and   just don’t work. Why don’t riders spend a few more $’s and buy a Bunn Breather Kit, with valves designed for bikes and warranted to work?    Copyright © A.R.Bunn 2009   

About 1% of clients ask me this when buying a Bunn Breather Kit. For years my reply was, “Breathe to air. Only 300,000 classic bikes survive. There’s no requirement to limit emissions on these bikes and conserving them is in the public interest”. Recently, I asked myself was this still valid, as we breathe more new bikes. In looking into the matter I was surprised to find a very grey area, covered below.

 Q1- How serious are motorcycle emissions? The US govt. still drives regulations internationally, so a first quote from them… 

“Nationwide, highway motorcycles are significant contributors to mobile-source air pollution, currently accounting for 0.6 percent of mobile-source hydrocarbon (HC) emissions, 0.1 percent of mobile-source oxides of nitrogen (NO_X) emissions, and less than 0.1 percent of mobile-source particulate matter (PM) emissions.”Control of Emissions From Highway Motorcycles  [Federal Register: January 15, 2004 (Volume 69, Number 10)] 

Q2. What are the regs on Bike Emissions? Again, let’s let the Americans loose on this one… 

“Motorcycle emission standards were first established in 1978 by the EPA and have remained unchanged since the 1980 model year. Those standards are 5 grams per kilometer hydrocarbon and 12 grams per kilometer carbon monoxide (5 g/km HC and 12 g/km CO...the national standard beginning in 2010, sets a limit of 0.8 grams per kilometer of hydrocarbons and nitrogen oxides and 12 grams per kilometer of carbon monoxide… EPA figures state motorcycles emit less than 1% of all mobile source emissions!...” (Bikersrights.com) 

Comment:- Nothing about crankcase emissions here. Let’s dig a bit deeper. 

Q3 Are there any exceptions to these regs? Riders are exceptional people. It’s natural to look for exceptions we may exploit. Here are a couple of potential loopholes… 

3.1 One-Off Bikes-“…for Special volume-limited compliance exemptions include for a person manufacturing a motorcycle for individual use (max. 1 per individual per life time of the provisions)…” Comment:- If we  e.g. restored  a classic or significantly customised a bike; this exception might apply?  

3.2 Useful Life- Govts. specify a service life for bikes of 5 years or 30,000kms. Outside this, you may argue the emission controls don’t apply. A legal precedent would be handy.

3.3. Used bikes?- The EPA emission requirements don’t apply to older bikes. If you ride a pre-1978 bike, you are free of emission requirements.  You can breathe your crankcase to air. The 2006-2010 regs apply to bikes with those model years. One workaround is to buy a good low-mileage 2005 or 2009 bike, and keep it.  

Q4- What about Crankcase Emissions and the Bunn Breather Kit? Discharging crankcase emissions to air is prohibited from new bikes. Bunn Kits can be fitted to discharge to the airbox or to ground. It’s the rider’s choice. The majority of clients ride older, classic or vintage bikes vented to air, and so comply with worldwide requirements. With new bikes, riders have to make a choice. This is clear enough in western countries where a wide array of aftermarket air boxes and breathers are sold, most designed for open breathing. There is no testing of crankcase emissions in any country I ride bikes. In fact there is not even a  test for crankcases emissions. In the EU there’s a visual check of crankcase: in the US none, and none downunder. All I can find is the 1996 Faiz World Bank report, where estimates of emissions were made from the contents of blow-by gas. The matter seems to rest there.

Air pollution from motor vehicles: standards and technologies for ... By Asif Faiz, Christopher S. Weaver, Michael P. Walsh 1996“There is no common procedure for testing crankcase emissions across countries. European regulations specify a functional test to confirm the abscence of venting from the crankcase., while US regulations simply prohibit crankcase emissions. Uncontrolled crankcase emissions have been estimated from measurements of volatile organic compound concentrations in blowby gases. On vehicles with closed crankcase ventilation systems, crankcase emissions are assumed to be zero.”

This inter alia explains the bizarre, maze-like design of Royal Enfield breathers to 2008. These passed visual EU checks, and satisfied the US, i.e.  with so many tubes connecting all compartments…it was impossible for gas to find a way out! This maze continues to baffle Bullet riders. 

Q5- How Significant are Bike Crankcase Emissions with a Bunn Kit?

As motorcycle emissions comprise 0.001-0.006 of vehicle emissions, we can break down crankcase emissions vs exhaust pipe emissions, to answer this.  

Conclusion:- Four-stroke motorcycles make no statistically significant contribution to global pollution. There is no evidence to support this claim. Crankcase emissions are 0.001 of bike exhaust emissions.  There is even less evidence to ban crankcase emissions at 0.0000035 of total emissions. Where a Bunn Kit is fitted, harmful effects from crankcase emissions are further reduced by air injection. I’ll look at this subject again in a few years.

The Bonnie is the most successful classic bike of all time, judged in terms of world-wide sales and market share over the greatest number of years. Like many British motorcycles, it enjoyed ongoing changes to its crankcase breathing system, as designers tried to find an effective breather, with varying success. Similar changes to the lubrication system went along, and sometimes these impacted on breathing performance.

 There were so many changes riders are often unsure just what breather and lubrication version they have. Knowing this can lead to improved breathing and performance. Hence the need for a first ‘breathing development history’ of the Bonnie; as today’s riders continue the search for optimal crankcase breathing performance.  This paper logs annual Bonnie breather design development. For convenience it summarises the breather and associated lubrication system design, which together comprise the breather system for each year of production. Years of unchanged design are grouped. This article draws on Nelsons work along with Chilton, Haynes and Bacon, factory records and publications and our client and testing files. 

1959-1960 The first Bonnie carried the inlet camshaft timed breather found on other post WWII Triumph models. This used a disk with two cut-outs and a valve with four apertures. These coincided twice per camshaft rotation, allowing air to pass on every downstroke. At least that was the design intention. The breather was vented to ground by a union adjacent to the gearbox sprocket. The oiltank was vented to ground. Despite Nelson’s notes, there does not seem to have been a froth-tower on these first Bonnies. I’ve not applied gauges to one of these models, but the OEM breather probably performs like other timed breathers with big pressure swings, little air flow and varying over-pressure. We can do better today. 

1961-62 A new oil tank included a froth-tower vented to ground. The engine breather continued unchanged. 

1963-64 The new unit engine design revised the timed breather to try and reduce crankcase pressurising. The vent pipe was T’eed with the oiltank vent pipe. The sump was redesigned to improve scavenging. This would also have assisted breathing.

1965-66 A new 6 pint oiltank with a new froth tower and chain oiler. Of great interest to us now was the addition of a timing plug drilling behind the barrel.  From 1965-1981 this drilling performs beautifully as a breather union utilising it’s ½”UNC thread form, and especially it’s access to the prized low-pressure zone around the flywheel.

1967-68  A new oil pump design boosted scavenge capacity, hence increasing crankcase breathing also.

1969- Oil pump feed flow was increased and the scavenge pick-up lifted 5/8”. These changes were hoped to ease a chronic camshaft wear problems. [They were unsuccessful and later nitriding fixed the problem.] The oiling changes would not have improved breathing, and owners of this model may encounter increased oil burning and oil venting via the breather.   

1970- This was an important year for Bonnie breathing, marking the abandonment of timed breathing. Triumph opted to return to an older in-house breathing method wherein engine and sometimes oiltank, had vented to the primary chaincase. This in turn vented to air via e.g. a chaincase oiler.  History doesn’t record whether the change was  forced by Umberslade Hall or was a purely Meriden matter. I think the latter.  

The Bonnie variant of this technique involved drilling three small holes in the drive-side crankcase, forming a weir and allowing sump air to pass into the chaincase (and vice versa). A new, rather ugly large-bore union was installed on the top rear chaincase and this required a baffle to stop oil fling up the tube. A very long breather tube rose up to the rear guard and followed it back to the number plate; where it vented oil and blow-by onto the road. Along it’s course it T’eed with a pipe from the oil tank froth-tower.  Another new oiltank came along, of reportedly 5.5pints.

NB:- There’s confusion over the actual capacity so owners would be wise to check this. It can be a common cause of over-filling and consequent oil venting the breather.

1971-1973 The advent of the Umberslade wet-frame gave another set of pipes and tubes. These seem to have been grafted on to the Meriden tube array from the year before, without much thought. This exposed one of the many black holes which opened up between the Meriden and Umberslade design teams. The already long 1970 breather tube array of roughly 1.5 meters, was further increased by the relocation of the oiltank breather to the front of the bike. This added nearly another meter to the existing long array. The consequences of this are explored below.  

1/ P-Traps The tube array starts up high at the front with the oiltank breather union. It then falls to connect in a “T” with the chaincase breather. The combined breather tube then rises again to traverse the rear guard. There is a probability of P-traps forming along the course of this breather array. In fact when you stand back , the whole breather array forms a giant P-trap,. Riders should inspect the tube path and reposition tubes where any dips are seen to occur.  

2/ Condensation- As above, the oiltank breather travels back down along the frame and Tee’s into the chaincase breather.  It traverses an extremely long run, effectively the length of the bike to the number plate vent position. There is perhaps in excess of 2 meters of breather tubing in this array. This is roughly four times the safe maximum exhaust breather run, based on my research! I suggest shortening it to enable better breather function.  

It is inevitable hot oiltank and blow-by gases will cool long before they can find their way to the end of this long tube. In Winter especially , condensation will occur and blow-by will build up in dips in the tube, forming an emulsified grease. This can eventually block the breather if left in place. Moisture that condenses out will seek the lowest point. Depending on the tube path, this may be the chaincase union, and extremely corrosive blow-by fluid may drain back into the chaincase, contaminating the oil, and increasing the humidity in chaincase and crankcase, which now has an open airway to the chaincase from this year. This is not good design, especially given the ‘moist crankcase’ future inevitable under ethanol fuels.  

3/ Pressure drop- The longer a breather tube, the greater the pressure drop. You can feel this by blowing down shorter and longer tubes. With breather tubes as long as 2000mm and rising, significant pressure drops are likely. These act to further impede the efficient purging of blow-by vapour from the engine, and hasten the formation of blow-by deposits.  Meantime the oiltank capacity shrank to 4 pints. On the face of it, this 33% cut in oil capacity since 1966, together with the increase in tuning and power, would cause higher operating oil temperatures. 

1974-1977 The only significant breather change was to the chaincase breather union, which changed from metal to black plastic in 1974. Otherwise the breather seems to have been ignored till 1978 when US EPA requirements forced  the next change.  

1978-1980 This generation of breather implies someone at the Meriden Coop was thinking about breathing, and for the first time in years. The US EPA benchmarks could only at that time be met at the Coop by a recycling breather. The smart first step was to think in terms of the above criticism, and shorten the tube array. First the oiltank was vented to the rocker boxes. This required a very short tube and dissected out nearly  1000mm of tube from the previous bloated array. Next the chaincase breather was connected into the airbox, where the low pressure (albeit varying) would assist breathing, at least over some part of the rpm range. This also greatly reduced its breather tube length.  

The next creative step was to install what Meriden  termed a “breather tower”. This was not like a froth tower, but more a means of releasing blow-by vapour into the carby intake, as a vapour vs gobs of slurry. The design seems to be borrowed from a MIG welder diffuser head and indeed its function must have been to diffuse vapour; whilst minimising fouling of the new fuel charge. It’s second function (or at least effect), would have been to drain condensate back to the chaincase. The erect position of the tower and it’s placement inside the airbox point to these conclusions.  This breather further shrank the breather tube run to now efficient proportions. Pressure drop and condensation were overcome, instead being replaced by carby, airbox and air filter fouling, thus joining Bonnie owners to the legions of Harley riders.  But the EPA was happy.  

1981-1984- A first for any manufacturers Parts List…the breather actually gains an entry in the index and even its own illustrated page! The same creative hand is evident this year, with a subtle change to the breather tower design. A wee stand-pipe was included, apparently to try and tune the breather. He introduces an extension into the RH airbox breather tower, penetrating the airstream entering the carby.

This simple idea, perhaps derived after hours at  the Meriden flow-bench, would most likely been to try and  overcome any gobs of blow-by pumped up into the carby at high speed. He would have been trying to find a sweet-spot between the pumping action of the breather and the sucking action of the airbox….a thankless task. 

1985-1988 The Harris Years…Our long-forgotten hero [was it Brian Jones?] is still at his post. The breather tower extension is now angled up and extended further. This probably was to increase case breathing at mid-high speeds when blow-by is least and  dynamic vacuum in the air intake at its peak. I wonder if he was happy with the result? I  doubt it. At this point my records run dry. Harris production ceased in 1988 and most likely this breather design carried on till the end.

Looking back it was a ceaseless search for effective breathing. Most of the changes brought little advance. Some were backward steps. Others were forced by external events e.g. EPA. With the advantage of hindsight, and our present research base, they missed many opportunities over those thirty years to make stepwise improvements in breathing. This year, fifty years after the Bonnie’s birth we are steadily growing the know-how to make the Bonnie engine breathe and sing.  Given the Bonnie’s status we concentrate on her breathing, as we review and design succeeding years Breather Kits. Whatever year Bonnie you ride from 1959 to 1988, we can assist you and her, to breathe and perform.

Copyright © A.R.Bunn 2009

Background:- Back in 2006 we consulted to Royal Enfield Australia to resolve breathing problems with the Classic model. In 2007 we moved on to resolve similar problems with the Electras. Before introducing the new Bunn Kit, I recommended independent road-testing by Electra riders, to ensure the new Kit performed under actual UK and Oz road conditions.  

The full report of that international trial has not been published, till today. It is published in full, below.

Today, three years later a new Enfield engine appears.   The design appears to evolve from the old engine. Thus, it may need additional  breathing help to perform acceptably.  It will be interesting to  observe rider reports during it's first year of service. We will develop a breather kit for it, if needed.

Anglo-Australian Riders’ Crankcase Breathing Trial  

  Royal Enfield Electra   and Bunn  Breather mkII                     

March-April 2007, Final Report  

Summary: - Six Electra riders in UK and Australia tested the new Bunn mkII Breather for the Royal Enfield. On all bikes the mkII Bunn breather out-performed the OEM breather. On all five stock Electras the new mkII breather worked normally, exhausting blow-by and sumpwater, while preventing oil spitting from the breather. It did so over a range of speeds, riding and weather conditions.

                     On the one performance-modified bike, oil spitting occurred at high speed. This bike was running in new barrel, rings and piston and is discussed in Appendix II.  

                    We conclude the Bunn kit mkII is an effective breather for the Royal Enfield Electras, whether running in UK or Australian conditions.

1.0 Background- Over October-November 2006 Carlel Classic Restorations consulted to Royal Enfield Australia over crankcase breathing for Classic and Electra models.  Development trials were conducted on an REA 2006 Classic and breathing problems resolved with Carlel’s patented DAPPER-Technology. Mirror trials on the Electra were undertaken by REA and its breathing problems also resolved. The breathing solution was made available commercially as the Bunn Breather Kit for the Royal Enfield.

                      Feedback from Classic riders was excellent. Feedback from Electra riders was mixed with some reporting oil venting with the OEM breather, had not been rectified. In March on a 2006 REA Electra I reproduced and diagnosed the symptoms and devised the solution. After successful development trials of the mkII Bunn Breather Kit, REA and Carlel decided to conduct independent road tests in UK and Australia; to ensure the mkII Bunn Kit  works across bikes of different production dates, riders, riding styles, climate etc. A sample of Electra riders purchasing a Bunn Kit, were invited to join the trial. All agreed. Names and addresses are held confidential. All rider communications are on file at Carlel and/or REA.

Seven Riders entered the study, coded as below:-

Rider 1- Australia*

Rider 2- Australia

Rider 3- Australia*

Rider 4- Australia [self]

Rider 5- UK*

Rider 6- UK

Rider 7- EU-This rider was called on business to USA and did not return in time to install the Kit and report.

* These riders had experienced severe or total engine oil loss with the OEM breather, in one case seizing an engine.

2.0 Trial protocol- All Riders received  the mkII Bunn Breather  kit, or new parts to upgrade their original kits. All bikes save one in the UK were essentially stock bikes. One UK bike had a new barrel, piston and rings  from a previous OEM breather problem and was running in during the trial. This bike also had the PAV system removed; revised carburation and high-flow air intake with a performance exhaust system. This bike is discussed in appendix II. Riders were asked to ride their bikes for 50-100kms after fitting, and report findings to the author. No honoraria were offered, save the upgrade to riders with an earlier version kit.

3.0 Findings-

 3.1 All riders of stock Electras in the UK and Australia reported  the mkII breather preventing oil venting the exhaust breather, while purging sumpwater and blow-by.

3.2 The one modified Electra reported similar results except at high speeds i.e. 105-110kmh, where oil passed the exhaust breather.

3.3 Some riders reported oil entering the Inlet line at high speeds, and pumping out again at lower speeds. [Oil normally cannot exit this line due the valve.]

3.4 There were typical reports of an improvement in engine power, e.g. “…The engine pulls stronger and smoother, quite impressed….”

4.0 Conclusions-

4.1 Every stock Electra in the trial achieved effective crankcase breathing without oil loss, whether running in freezing British Winter nights, cold Australian mountains [9-14C] or at sea level in Australia.

4.2  Some performance and racing Electra engines may need extra breathing capacity.

5.0 Recommendations

5.1 The Bunn mkII Breather kit for the Royal Enfield Electra is suitable for fitting to stock Electras under UK and Australian conditions.

5.2 The mkII kit may also be fitted to the Classic, although that model is not as prone to oil venting as the Electra, given its less developed engine.

5.3 The usual caveat applies to modified and race engines, i.e. additional breathing  may be required.

Rider reports are quoted below. Personal and extraneous matter was edited for clarity and to respect rider privacy.

Rider 1- Australia*

“…the modified kit seemed okay on the Electra over Easter, although this bike was never overly problematic like others. I did notice more clouding early in the morning, probably from more moisture in the air….”

Rider 3- Australia*

“…The big thing I'm looking for is the removal of water from the oil.  With short runs and in cool weather, when draining the oil I get up to 40cc of pure water and some emulsified as well.  Early in the piece before I discovered this water build up problem, I thought I was going mad, as my oil level was going up.  I went on a run on a very hot day and when I got back my oil level had dropped dramatically, very scary until I worked it out….”

“… First impressions.  The [Bunn] kit is snap to install, my only suggestions would be to have a blanking off pipe for the air box pipe provided in the kit and the filter could be one of those with a stud on top to enable attaching to the arm that the blow-by canister.

On completion of the install (late Sunday) I ran up the engine to hot and was amazed to see condensation forming in the exhaust tube within 45 secs of start-up, see attached photo.  Unfortunately I had no opportunity to test ride it.  One observation, the exhaust flapper valve is quite loud, much like a click beetle….”
 

“…Today; starting from cold (10deg) is no different but the engine came up to speed quicker necessitating closing the enrichener within 1 min of starting.  Once again the exhaust tube misted up quite quickly.  The engine pulls stronger and smoother, quite impressed.  My ride to work is quite short 10 Km and in that time there was heavy condensation in the tube and no sign of any oil….

“… normality appears to have been reached.  By the way, I'm off on a 700Km ride… on Saturday, I'll tell how we went next Monday….

“… the weekend wrap-up; apart from the rear tyre blow-out 50Km from home (it nearly spat me of) all went reasonable well.  We did 630Km over 9 hours with many stops, I stuck to 100Km all day and used 50cc of oil, very happy.  At no time was oil visible in the breather outlet and on inspection of the end of the pipe only bypass fluid was present.  The inlet is a different story, on a least three occasions at speed I noticed the inlet pipe flood, oil would fill the pipe for at least 4 inches of the pipe and did not clear completely until the engine returned to idle where the pumping action would clear the line….”

“…I do agree with you that it’s not a problem with your breather, as the [Inlet] line fills when not under suction and empties when suction returns.

Rider 4- Australia [myself]

“…No oil spray gets past the secondary baffle. Moisture above the baffles shows sumpwater is being  ejected. The usual few brown blow-by droplets at the valve. A few drops on day one only from the chaincase line, as built-up blow-by emulsion from the OEM breather heated  up and dripped out. After the first few runs, the garage floor remains clean under the breather. Occasional  oil traces in the first few inches of the Inlet line, that gets pumped back inside. Road-trials included hard pillion riding with 25 stones of rider and pillion….”

“…I conducted high-speed tests today with the mkII breather on the 2006 stock Electra. Over a 1.5 mile test-strip of sealed road [with 100kmh limit], I completed seven runs, reaching 110-120kmh on each run. I eventually gave it away as a radar police car chose to end his Easter holiday monitoring, right where I started my test runs. After meeting him twice, I had no desire to lose my licence, as it's "double-points" loss over Easter.

My results were-

1/ Over the seven runs, I was unable to reproduce the OEM Electra behaviour of spitting oil out the Exhaust breather, or the similar modified Electra behaviour.

2/ Looking down into the Exhaust breather line on every run at 110-120, there was no trace of oil above the lower quarter of the primary metal baffle. 

3/ The secondary baffle remained clear.

4/ The tube above the secondary baffle remained crystal clear, up to 120kmh [75mph].

5/ Nothing came out the Exhaust valve except a tiny amount of blow-by steam. The rear tire was untouched. The frame was dry. The oil tank level was slightly over-full to start and after 250kms running today, had not dropped at all when I checked it at home.

6/ Throttle openings for the trial were roughly 1/4 open =90kmh, 1/2+ open= 110-120kmh. The bike feels under-geared at these speeds.

 7/ Oil came into the Inlet breather line at 110-120kmh on occasion. As other riders report, when the rpm drops, the oil rapidly pumps back into the timing case. It is impossible for oil to get past this valve, so this finding is incidental.

NB: This Inlet line behaviour is reversed in the Classic, i.e. oil comes into the line at idle and is pumped back at speed. My hunch is that at these high-speeds, the two small Electra oil return holes are under the oil level in the timing case and tank. This stops my valves communicating for a time, till the oil level restores. Pressure builds up in the timing case on every second rev, and oil pushes into the Bunn Inlet line, making it act as a surge tank until speeds lower, when it resumes pumping. This is a useful feature of the system and helps explain how the Bunn Breather copes where the OEM breather fails.

“… update on the changes to the breather system you recommended. Fingers crossed and I think we have a winner! Installed the new wire filter in the outlet pipe, as shown, and I am pleased to report it seems to stop the oil mist getting into the breather pipe. Observations show that oil gets into the bottom of the pipe and reaches the gauze, here it can creep up a little, but doesn’t get any further. The colour of the oil is normal and doesn’t become white. At tick over the oil in the pipe drains back into the sump if it has accumulated in the gauze. There is still condensation in the breather pipe, but it is water and not an oily mist. Will let you know more when I have had a long run, but things look good…”

“…, a little update with regards to the oil tower we are trying out. I have ridden the bike during the day with no problems and as I reported the oil stays at the bottom of the tube occasionally reaching the mesh. It stays a nice brown colour, with the only deposit in the breather tube being water vapour. The other night I rode to a friend’s house about 8 miles away, with the air temperature about 5 degrees C. Don’t know what the wind chill factor would have been! On arrival I noticed that there was some white oil in the tower tube, this drained back never getting past the top foam. I think the low air temperature around the tube (possibly in the region of freezing) may have caused the emulsification. I am considering putting a layer of foam around the tube (the kind we have for insulating central heating pipes) to see if there is a benefit on cold days. Will let you know the results…”

Rider 7- EU- report to come.

                 A larger carburetter, high-flow air filter and tuned exhaust are simple ways to increase power by ~25%+, improving volumetric efficiency at the cost of fuel consumption. A higher state of tune requires greater crankcase breathing capacity. Unless this is provided, the crankcase may pressurise.  This is demonstrated in the case of Rider 5 below.

Rider 5- UK* 

        This Electra is owned by a very capable rider, who has tuned and modified the bike e.g.  PAV removed, Amal carby, high-flow air filter, custom exhaust system, and smaller rear sprocket. These changes increase power output over stock Electras and call for further breathing capacity. It was also running in a new barrel, piston and rings at the time of the trial. Coincidentally it responded differently to other Electras in the trial.

“…thanks for the information. From the photograph, the new exhaust tube looks interesting. I notice that his intake tube is lying flat along the top of the engine casing. I had mine set up like that initially but found that oil was getting into it from the timing case. I looped it up with the exhaust tube and secured the two together with a cable tie. No oil has entered the intake tube since. I secured the intake filter to the rear battery bracket screw with a 'P' bracket around the tube. This provides a simple and neat mounting which is well protected from the elements by the battery cover…”

“…The good news is that the Mk2 exhaust tube arrived yesterday. I fitted it when I got home from work and took the bike out for a run. The temperature was 7 degrees centigrade so was a bit cool but not particularly cold. I rode for a few miles through the urban sprawl at 30 to 40 mph to warm up the engine and then out onto some faster roads at 50 to 55 mph. After about 10 miles I stopped to check the breather. All was well. There was a little oil bubbling in the gauze filter in the exhaust tube and the rest was completely clear. (no oil in the inlet tube despite no duck bill). I was rather pleased with this result and headed for some long straight roads where I could get some speed up. As the new piston and barrel have only done 700 miles I didn’t want to thrash it too much so a couple of short bursts of 70 to 75 mph were all I dared to do. I have fitted a 19 tooth gearbox sprocket to the bike so this speed probably equates to 65 to 70 mph on a standard Electra.

After completing the “fast” run I pulled in to inspect the breather again and here is the bad news. The exhaust tube was full of emulsified oil and there was the usual oil deposit all over the centre stand. So my conclusion after one test run is that it works well up to about 55 mph. I think that what may be needed is a small in-line canister, with a mesh filter, just above the oil tank outlet. This larger volume would dissipate the energy of the oil and gases entering it and thus only the gases would escape under pressure through the top into the exhaust tube. Just a thought. I think the Mk2 kit very nearly solves the problem but a Mk3 design may be needed to solve it completely….”

“…Thanks for the information and your suggestions. This gives me a few things to try out. It may take some time as I realise it's important to test each modification separately to gauge the effects accurately. I'll start with a compression test and then move the mesh baffle up the pipe a bit. This may be enough to solve the problem. Perhaps a longer piece of mesh is needed. If it looks as though it might help, I'll give it a go. If not, I'll work through your other suggestions and I'll let you know how it all goes….”

““… the compression test, which was 110psi.[significantly lower due to new barrel, piston and rings RB]…The second task was to push the mesh baffle and sponge filter higher up the exhaust tube. I rode the same test route at the same speeds as previously and there was no noticeable improvement. I bought a sheet of fine aluminium mesh and made a longer and more tightly rolled baffle. I fitted this and the sponge into a 150mm length of 10mm tube and pushed the exhaust valve into the top of it. This then fitted onto the engine. A tail of 10mm tube attached to the valve completed the job. I then repeated the usual test run to try it out. It succeeded in preventing oil from getting past the mesh but there was a lot of oil in the inlet pipe. I suspect that the new baffle was restricting the exhaust tube, creating unwanted crank case pressure, which was forcing oil out through the inlet pipe despite its one way valve. I tried moving the inlet valve to the timing case end of the tube but the oil passed straight through it (against the valve action)! So, I had to find a way of preventing oil escaping through the exhaust tube without introducing a restriction. I bought two cylindrical (car) crank case breathers which had end caps with 12mm pipe fittings exiting at 90 degrees and were filled with wire filters. I cut one of the cylindrical containers in half, filled it with one of the wire filters and fitted the end caps on each end. I cut the 90 degree bend off the original 10mm rubber tube and attached this to the bottom end cap and onto the engine pipe fitting and ran the exhaust tube with the valve in the end, from the top. This provides a 60mm diameter by about 40mm high canister with 90 degree inlet and outlets. I refitted the duckbill in the timing case and installed the inlet pipe as per the original instructions. The usual test run, with the engine oil at the “Full” mark, had a surprising result. Absolutely no traces of oil in the exhaust tube but an unbelievable amount of large droplets of clear water. Far more than previously. I reckon your breather is working even more effectively than with just the plain tube. The water was still condensing in the tube after 20 miles, which I am pleased about because otherwise it would still have been in the engine…

I’ll have a go at your idea with the primary case, which sounds interesting, although I have some concerns about trying this as I’ve heard of some Electras, with the original system, which have filled their primary cases with engine oil. I use ATF in the primary so I wouldn’t want engine oil in it, or ATF in the crankcase! Joining the two sounds a bit risky to me. Also I wonder if it would reduce the effectiveness of the inlet breather with regard to the crank case. Mine seems to be working exceptionally well now, judging by what’s coming out of the exhaust tube! May be another solution is to maintain the oil level below the transfer holes between the timing case and the oil tank. I’ve wondered about enlarging these holes………or not!...””

             NB:-  While Rider 5’s performance solution is working nicely, it is not the only solution available for performance and racing Bullet engines. Indeed, given the various breather and oil drilling mods made in India, there are now ~100  possible ways of breathing the Electra engine. Another solution uses the chaincase as extra breather capacity i.e. as a plenum chamber or negative vacuum vessel. This involves connecting the timing and chaincase breathers via the Bunn Inlet line, using e.g. a T-piece below the air filter and valve assembly. The ~2-3 litre space in the chaincase should cushion the greater air pressure fluctuations, before they reach the oiltank. Care needs to be taken to ensure oil migration does not occur into the chaincase.

                  This one modified Electra was normal at club run speeds, but at 105-110kmh resumed venting oil. The carburetter, air filter, PAV and exhaust modifications to this bike give it greater power and greater blow-by. The new barrel, piston and rings accentuate blow-by pressure in the crankcase, [as cylinder compression was only 110psi.] Greater speeds and blow-by can increase engine temperatures and crankcase air pressure.

                    I tried to reproduce this venting by pushing a stock Electra past this speed to 110-120kmh, but was unable to produce any oil venting at all. The mkII breather remained free of oil up to 120kmh [75mph].   Thus we regard this bike as an atypical result compared to the other trial bikes.

The B50SS Gold Star is now a rare collectible, with outstanding performance like its racing predecessors. 

BSA never really sorted out their singles breathing, as evidenced by the changes and modifications down the years. This last Gold Star is a good example of the BSA breathing design dilemma, as it came with not one but dual breathers!

Both the older  timed shaft breather and the new Meriden-derived 1970 Triumph open breathing via chaincase were fitted, to try and improve matters. 

When we test this model, the OEM breathing is still unacceptable: too much air sucking and blowing through the chaincase, with crankshaft drag and the risk of dirt entering the chaincase. The tandem timed breather contributes little to relieve matters. The saving grace was the new oil pump fitted with more coarse teeth for increased delivery and scavenging. This probably does more to assist B50 breathing than the new chaincase breather, though its role here is never recognised.

 Pictured  below is a new breathing solution for these models. Using a 2009 Bunn Classic Kit, we connect into the forward timing drilling, (shown in front of the barrel) and the OEM chaincase breather union (shown at top-rear of chaincase). This provides a  Bottom>>Bottom  breathing solution which smoothes out the violent swings in pressure and flow from the old breathers.   

   Reporoa Crankcase Breathing Trial 

        Goudies Road 10/10/2009                         

Requests for email copies of the full report to rexbunn@bigpond.com .

NB:- See articles 6/, 23/, and 53/, for previous research on power gains. 

1.0 Background- Following 2007 requests from US riders for more information on power aspects of crankcase breathing, I organised US dyno trials to follow up prior NZ, Oz and US dyno trials. These were set around 2008 Speed Week, but were delayed and I missed them. When later held in Denver (the ‘mile-high’ city), they proved equivocal. In analysing the findings, we stumbled over the unreported effects of altitude on crankcase breathing.

As most riding is done at significantly lower altitudes, sea-level dyno trials were arranged to overcome this, when ongoing research showed dyno trials were in fact unlikely to measure such breather performance. This is due to aerodynamic and engine load factors associated with Bunn Breather performance. A stationary tethered bike, sans rider, with brief artificial engine loading, and an abnormal airstream flowing over the bike; all contribute to dyno testing being not truly representative of real on-road conditions... It became clear fixed-throttle speed-trap trials were the best, perhaps the only way forward. Suitable safe roads for this are rare, see  http://webmonkey.wired.com/special_multimedia/2008/pl_motor_1607

Goudies Road in New Zealand proved a nearly ideal speed-trap site. It was recently closed to public access.

       2.1 To gather evidence of any difference in elapsed times, between breathing via ‘open’ crankcase and via the 2010 series Bunn Kit.  Differences would indicate a change in power.

      2.2 To collect data on crankcase breathing pressures at high engine speeds and under wide-open throttle (WOT).

      2.3 To detect any gross change in breathing at WOT due to ring-flutter.

NB: - The trial was not a comparison of Harley-Davidson OEM breathing and the Bunn Breather.  Blow-by dilution and contamination of the fuel charge from OEM recycling, with power losses possible, could advantage the Bunn breather. The trial tested the Bunn Kit against open breathing, i.e. where Bunn and Harley-Davidson head-breathers each vent to air.

 

3.0 Method: - A one kilometer speed-trap was constructed on a North-South section of Goudies Road, Reporoa, New Zealand. Altitude was 546m at the North station and 547m at the South station. Temperature was 10C dropping to 9C during the trial. A 0.3% RAD correction was made. A fresh to strong breeze (Beaufort 5-7) gusted from Norwest round to South-East. This along with a rising grade to the South, contributed to directional timings. A wind-break of pine trees partly shielded the rider. The three-man road-crew volunteered to supervise the trial. Traffic interruptions occurred and UHF communications enabled 'stand-bys' to be called. A harrier disputed the white line at centre course, over a road-kill possum. Bird-strike from a flock of finches along the road, baulked early runs.

The stations timed each run, with station times averaged to control for measurement error. Runs were repeated where time-keeping errors occurred. Several practice runs were made to enable timekeeper accuracy and station coordination. Some thirty runs were made in all. The first suite of runs used the 2010 Bunn Kit at ¼, 1/2, 3/4 and WOT (wide open throttle). North and South runs were made at each throttle opening, to control for windage, and the times averaged. The breathers were then changed and the second set of runs undertaken with open breathing. The throttle was fixed at marked openings using a friction device.  During practice and up to ½ throttle runs, the rider trailed the right hand while negotiating the trap, to avoid dislodging the throttle. For high-speed runs, safety required the rider to steer with both hands. The rider monitored a damped UBW pressure gauge recording crankcase pressure, along with engine temperature gauge and throttle setting. Valve function was observed where safe to do so. 

The trial vehicle, a 2008 Harley-Davidson 883C Sportster was stock; save a K&N air filter, modified breathing, and long oil filter and cooler. Oil tank temperature averaged 65C and varied by +/-5C during the runs The MoCo umbrella valves were left in situ and non-functioning, failing blow-testing as is common with these engines.

 

Given windage etc, the run-up and braking distances were progressively increased through the day. The same turnaround points were used for matched North and South runs. In examining the data, run-up distance for WOT runs might have been increased, but cross-roads made this hazardous.

4.0 Findings-

   4.1 Elapsed Time Findings- In table one below the main elapsed time findings are compared:-

Table 1 shows a mean difference of nearly 3% between the two breathers, measured as the difference in mean time to pass the speed-trap. The maximum 7% difference was at ¼ throttle, and fell away by ½ throttle, disappearing by ¾ throttle. AT WOT open breathing was marginally ahead. The difference in elapsed time between the breathers was most apparent at lower rpm. This is consistent with earlier New Zealand V2 dyno data, but differs from the 2007 US V2 dyno data, where a significant difference was apparent near WOT. This may reflect the different research methods, and breather design differences between 2007 and 2010 series.

4.2 High-Speed Crankcase Breathing and Pressure Findings -Workshop records of crankcase pressure and flow are taken at necessarily lower rpm and load. The crankcase at higher rpm is less well charted, especially under road conditions. In Table 2 below are summarised the crankcase pressure readings taken during the trial:-

In Table 2 above, the case pressure median and range differences between the two types of breather are marked. Open breathing pressures oscillated widely around the median pressure, despite a damping flow restrictor inserted in the line. By contrast Bunn Breathing had significantly less gauge deflection, less violent needle movement and lower case pressures. These differences were noted throughout the rpm range, and may not be due to extraneous e.g. resonant factors associated with a particular engine speed. More research will be undertaken on this.

Open breathing is characterized by a wider range of pressure swings. Pressure variations up to +/- 45mmHg were recorded on this trial. These reflect gases in motion from unrestricted piston pumping, with parasitic power loss to the crankshaft. This varying over-pressure also contributes to oil leaks.  The Bunn Breather maintained lower consistent pressures, with up to +/-10-25mmHg variation around median pressure, over the rpm range. Pressures never exceeded atmospheric. This is a good illustration of the benefits of multi-valve arrays in managing the crankcase.          

The open breathing results accord with those seen on open breathing engines generally. They typically stay at or above atmospheric pressure. The crankcase connects with the atmosphere, and pressure equilibrates inside and out. As Bell notes, if case pressure drops below atmospheric, the oil scavenge pump sucks air into the crankcase, (admitting dirt) and raising case pressure. This increases pumping losses and contributes to power loss; giving sufficient reason to abandon open breathing.

The 2010 Bunn Kit is designed to operate the crankcase at lower pressures than previous Kits. Case pressure drops quickly above idle. By ¼ throttle and under load, pressure drops steadily to ½ throttle and continues to drop smoothly till 3/4 throttle. It then appears to reach an asymptote by WOT.

I had expected to detect a pressure increase near WOT, as evidence of any ‘ring-flutter’. None was detected. The case vacuum was maintained right up to and at WOT. Paul de K. Dykes first noted this ring-flutter phenomenon in 1947. It manifests itself as an increase in blow-by occurring near WOT. The onset of ring-flutter in this engine is calculated to occur near 6,000rpm, which is also peak rpm for this engine. The tacho and speedo were not monitored during the trial, but the engine would have reached close to this rpm.

The abscence of ring flutter, pressure increase or breather flow overload at WOT, demonstrated the Bunn Kit is capable of handling peak airflow and pressure over the rev range in such engines.   

5.0 Conclusions-

The principle of using elapsed times through a speed trap to detect differences in engine power; is well established. It is after all, the basis of motorcycle racing. On these trials we recorded an 8% speed increase with this Kit at constant throttle. This Kit also recorded the highest crankcase vacuum we have achieved to date i.e. 11% vacuum.The margin in this research seems practically significant, if only because 1/4 throttle coincides with road speed limits, where road motorcycles spend much of their time. The results are also consistent with developing engine theory, as it relates to crankcase breathing. Apart from answering the question from riders interested in more torque being delivered for the same throttle setting, the findings suggest new research avenues to improve crankcase breather design.

In table 3 below are shown the significance testing results.

The case pressure findings are statistically significant. While striking, the time findings are not. This raises the question of engineering significance vs statistical significance, for the two do not always agree. We need to consider whether a 3 second difference through a 1km speed-trap at ¼ throttle, is practically significant. Riders will have to decide this. For us, it is further confirmation our research is well-founded.

The drop in elapsed time correlates with drops in crankcase air pressure. Such correlation explains why crankcase breathing is a research priority today for motor racing teams, and why some race car engines wear vacuum pumps. 

The case pressure results were useful confirmation our 2010 design handles the full range of engine operation. Interestingly the peak vacuum achieved by the 2010 Kit on this trial was 660-680 mmHg. This represents an 11-13% vacuum, a remarkable achievement for a low-cost, breather system relying on crankcase displacement, with negligible parasitic drag. Such control of crankcase air volume brings us closer to e.g. IHRA levels, where vacuum pumps are used to reduce case pressure. It offers motorcycle competitors a way forward. 

 However, the challenge for road-bike crankcase breathing is not (in my opinion), the quest for power. The challenge right now is to assist classic and contemporary motorcycles cope with the extra moisture burden from ethanol fuels. Ethanol attracts water like a magnet. With many bikes already experiencing poor case breathing, ethanol fuels lead to sump-water and increased corrosion damage.

The 2010 Bunn Breather is the only motorcycle crankcase breather designed to actively pump out accumulating moisture and sump water. This makes it perhaps the ideal motorcycle breather for its time, given the march of ethanol fuels.

                                                        Copyright © A.R.Bunn 2009

This article could be read with Blog article 64/, (looking at timed breathing wrto ignition and valve timing, and custom bikes). 

Timed breathers had a heyday up to the 1950s-60s on British bikes. They were also popular on US bikes. A timed breather, say a typical BSA camshaft breather on singles, comprises a drilled shaft running in a bush with matching cross-drillings. It connects the crankcase to the outside air, often via the timing case. When the two drillings coincide, gas can pass across. Otherwise the breather is blocked. This enables the designer to specify when the breather opens. He cannot however adjust it. Breathers on the camshaft mean the breather timing is locked at the original valve and ignition timing. A custom cam or new ignition may disturb it. Nor can he increase gas flow beyond a certain amount, lest he weaken components. It’s an ingenious, cheap and one would think effective way of lowering air pressure in the crankcase. This is fine in theory, but in practice it doesn’t work out very well, with unexpected effects on classic bikes today.

 Let’s start by following such a timed breather through an engine cycle, starting at the bottom i.e. BDC on the combustion stroke, soon after the timed breather has closed.   

Exhaust- On the next piston upstroke i.e. the Exhaust stroke, the breather shuts and the piston has to overcome suction in the crankcase, as no air is allowed in. There is a little drag on the crankshaft and this costs it some power loss. 

Induction-On this downstroke the breather remains shut and the piston has to compress air in the crankcase, as no air is allowed out. There is a bit more drag on the crankshaft. 

Compression- On this piston upstroke, the breather is still shut and the piston has to overcome suction again in the crankcase, as no air is allowed in. This is the third lot of drag on the crankshaft and a little more lost power. 

Combustion- On this downstroke, the breather can at last open, but only for a small part of the stroke; in fact for a maximum overlap of 25-30 degrees, out of the 180 degree stroke. For the other 150 degrees it stays shut. Designers often opted to place this small “breathing window” towards the end of the stroke, i.e. as the piston nears BDC. This is puzzling, as peak piston acceleration, combustion pressure, blow-by and piston downforce, all max out during the first half of the combustion stroke. Most engine torque develops in the first half of the power stroke. By 90 degrees ATDC, cylinder pressure and torque is reducing.  When the timed breather finally opens, the piston is slowing down, most blow-by has occurred, and the driving force on which the timed breather is relying: is largely spent. Blow-by in the crankcase is bottled up, causing violent pressure increases in some bikes.  

Conclusion- A timed shaft breather may stay shut for 1410 or more degrees of the 1440 degree engine cycle, opening only briefly at the end of the Combustion cycle. This means there is no engine breathing for 98% or more of engine operation; (save via the scavenge pump)…hardly an example of great engine design.  Even when the breather finally operates on the combustion stroke, there is no crankcase breathing for 83% of this down-stroke, including the period of greatest blow-by.  

According to Irving (personal correspondence), timed breathers should close no later than BDC. In this case they can open no later than 150 degrees ATDC, as they can only traverse up to about 30 degrees, depending on drillings. Of course this 30 degree opening is a fiction. The actual drillings are in complete alignment for a small part of this, perhaps for as little as 4-5% of shaft rotation on some BSA singles, depending on their size and shape.    

As the designer moved his breather opening towards BDC, perhaps to try and help more blow-by escape, he would run into another problem. Between +/- 20 degrees of BDC, there is very little piston movement. The piston is almost stationary. There is no piston movement to force air out the timed breather, for +/- 20 degrees around BDC.  It can only pass air compressed earlier by the piston downward motion between 0-150 degrees ATDC (and by blow-by). 

NB: - Air flow has inertia and air is elastic. I prefer to get crankcase air moving and to keep it moving, ideally in one direction. Compressing it repeatedly in a closed chamber over several strokes, before letting a little escape, does not seem the mark of great engine design. 

I think these are reasons why e.g. I can’t measure air flow out BSA timed breathers, and for the violent pressure swings I see in classic bikes e.g. Nortons, with timed breathers and bad oil leaks. Variants of timed breathers using disc/valve designs on e.g Triumphs sometimes had two vents, to try and provide more air passage. However,  similar limitations and criticisms apply to this design.

Timed breathers only work for a maximum 2% of engine operation. Isn’t it preferable to have a breather working the whole 1440 degrees of the engine cycle?  The Bunn Kit valves are ‘on duty' 180 degrees of every stroke. This must be a more effective way to breathe any engine.   

Unlike mass-produced bolt-on accessories, the Bunn Breather Kits are research-based and continuously developing. This week for example, we completed ton-up road trials of our next generation breather. The trial recalled the importance of valve positioning, to achieve optimal crankcase breathing.

 Here are latest tips for the best breather valve performance from your Bunn Kit. 

1/ Place Inlet valves with a run of tube to either side. Avoid the valve next to a banjo.

 2/ Ensure Exhaust valves angle down, to avoid blow-by condensing in the valve.

3/ Where possible, avoid having Inlet valves vertical. This valve works best lying down!

 4/ Position Exhaust valves no further than 500mm from the engine union.

5/ Attach a Draft Tube to the Exhaust valve, for increased performance.

6/ Ensure the Inlet breather line filter is out of the weather and out of the slip-stream.

7/ Keep valves away from exhaust ports.

8/ Avoid Exhaust valves dangling under the vehicle, where stones can damage them.

9/ Minimise breather tube length, for best performance.

10/ With badly worn or big wet-sump engines: two Exhaust valves may be used.

This article owes a great deal to two virtuoso classic engineers… Graham Bell and ‘Turbo Tom’ Wyatt. They describe the four stroke, air-cooled engine better than anyone. Wyatt died in 2005: Vale Turbo Tom. Graham Bell is still out there writing, researching, and helping a new generation of riders.  For Australians at least, he must be the greatest living classic motorcycle engineer, up there with Phil Irving. 

  Crankcase breathing is the orphan of the motorcycle engineering world. The other day I realised the body of work I’ve published on it, on this Blog and in books and magazines…rivals the total published since the dawn of motorcycling, at least in English. That just illustrates how little research was done during classic years. Yet blow-by (BB) is at last receiving deserved attention. I was recently told it’s one of the top three research priorities for world motor racing teams. In the search for performance, BB along with Friction and Cylinder Contamination, is where the R&D $ is spent this year. 

 BB is important for all riders because it happens in every engine, worn, old or new. It’s the passage of gases and fluids, descending past the piston, dropping into the crankcase. It occurs because a piston doesn’t make a perfect seal to the cylinder. The rings do not seal at all points and at all times. Gaps open up in three areas i.e. between ring and piston, ring and cylinder wall, and between ring ends. For classic riders these are also the order of importance for crankcase breathing. 

 The gases and fluids that pass down, vary over time. When the engine is stored, it is water from condensation. When it is started or stopped it is fuel from a rich mixture and water condensing in the combustion chamber. When it is running it’s unburned fuel plus exhaust gas, (72% Nitrogen, 14% CO2, 13% water and 1% acids, soot, nitrogen & hydrocarbons. Hillier 2006). It’s easy to imagine the corrosive soup this quickly makes in our crankcases, if ignored. 

What BB is and Where it forms are pretty easy to see. When it forms is the next question. What to do about it, is a more complicated question.  The When question is germane. In storage, condensation is inevitable. A dehumidifier is the only defence against BB in long-term storage (see Blog 46/). On start-up the best defence against BB is to get the engine hot and keep it hot, for long enough; so the engine can purge the soup, assuming the breather allows it. Under way, avoiding idle and WOT running will minimise BB.  

Let’s look more closely at BB over the road speed range, i.e. at idle, around town, and down the highway. If we graph BB against engine speed, we obtain a “U” shaped curve. BB peaks at idle, drops as you take off, and increases again near wide open throttle (WOT). This seems counter-intuitive but it is the case. Two things are happening and these affect breathing. At idle there is simply more dwell-time for BB to take place, as Bell tells us.  As speed increases in the mid-range, the piston spends less time in positions where BB occurs, so it declines. We expect little BB and good breathing where bikes spend the great majority of their running time, i.e. around 3000rpm. Where BB doesn’t decline in mid-range, we should suspect bore, piston, ring or valve guide wear. In classic and vintage bikes, such wear is often advanced. Cylinders, pistons and rings do not fit ideally, and BB can be more or less continuous. A cold cranking compression test is the first step, followed by a leak-down test. Best of all is a BB flow test to measure exactly what the engine is passing. Few riders have access to the latter two tests. 

  Near WOT an event called “ring-flutter” can occur. The top piston ring is forced or thrown off its land, after the sudden change in direction at TDC. Gas may build up between the top two rings and force them apart, allowing BB to gust past. Ring flutter was first described by Dr. Dykes of Cambridge Uni in his 1947 paper Piston Ring Movement During Blow-By in High-Speed Petrol Engines - P de K Dykes: (soon after the first study into crash helmets was completed by Cairns). We can estimate if/when our engines develop ‘ring flutter’ if we know four things…the stroke, conrod length, rpm and ring width (vertical height for some). Graham Bell provides a useful formula in his book Two Stroke Performance Tuning book, p155.

At http://www.bigboyzcycles.com/PistonSpeed.htm lies a useful calculator, based on Bells or a similar formula. We can easily estimate if/when ring flutter will occur on our bikes. For classic piston rings of 3mm width, the acceleration threshold is about 40,000 ft/sec/sec. As rings lose weight, the threshold goes up to approx 80,000 for typical 1.5mm rings and 140,000 for performance 1.0mm rings, say Villiers. For example BSA B25, Rocket Three and Triumph Tridents, with 1.6mm rings develop ring flutter by about 7,000rpm. For this reason, I never take my T25SS near this rpm. My Sportsters handle up to 6,000rpm before flutter starts, so in theory I should never experience ring flutter, as that’s about peak rpm.  It’s clearly more a problem for racers, and road-riders who alter compression, valve timing, and/or ignition timing etc.

  For all running engines, over the rpm range most BB occurs around and after TDC, on the compression stroke. This is because cylinder pressure is highest, and the piston is near stationary over 20 degrees either side of TDC on the power stroke. As it descends, it accelerates and perhaps could be said, to almost ‘leave the ring behind’ as it scoots down the barrel.   Over the rpm range other factors can contribute to BB. For example barrel wear is more pronounced near the top of the barrel. This is due to the piston rocking near TDC, poor lubrication and the extra abrasion of hard combustion deposits in this area. For classic and vintage bikes this is double jeopardy by BB. 

What to do about it? For vintage and classic riders, the question relates to conservation. The 300,000 classic bikes around the world have irreplaceable crankcases. Engines can be authentically and repeatedly rebuilt, IF you have cases. It they’ve corroded away due to BB, every lost engine represents 0.0003% of all surviving motorcycles on the planet. 

 For contemporary riders, it’s more about functionality and performance. BB causes unsightly emulsion, fouling air intakes and dripping down your leg. TBO, the time between engine overhauls is reduced, and servicing costs spike. For all riders, the growing reliance on ethanol fuel blends, means higher levels of engine moisture and accelerated wear. Purging BB from the engine is increasingly important. How then to purge?

Limited choice is available to riders. OEM breathers on classic and vintage bikes were rudimentary and not designed for ethanol fuels. Contemporary bike breathers recycle BB to the engine.  DIY open breathers at best expel some of the BB and moisture. Blow-by will always be with us. There is no cure. Reviewing options for riders, naturally I prefer a Bunn Breather. Nothing beats it for purging moisture and blow-by from an engine. It’s still developing and I’m its greatest critic. Each year, I set out to research an even better crankcase breather. We’ve sketched out the 2011 breather technology. The 2010 product range is largely completed. We press on. 

Some riders assume the Bunn Breather Kit is a Positive Crankcase Ventilation (PCV) device, like that in cars. It is not. While it involves passaging air through the crankcase, that’s about the only similarity.  

Car PCV systems are typically designed for engines of 4-8 cylinders, of inline or V construction, with large wet-sumps and water-cooling. There is no crankcase pumping effect. The ‘gases in motion’ move between rising and falling barrels. The air intake drives the breather. It recycles blow-by into the air intake. It uses one metering exhaust valve and one open inlet breather. The crankcase is thus connected to the atmosphere. Engines run at close to atmospheric pressure, increasing with engine wear. When wear advances or the PCV valve blocks, crankcase pressure spikes and the open inlet breather reverses flow and becomes an exhaust breather. The purpose of a PCV breather is to stop blow-by passing to ground. It has no positive effect on engine function, and can adversely affect it. 

 Bunn Kits are designed for engines with 1-2 (and some 4) cylinders, 360 degree crankshaft throw, inline, V or boxer engines with air-cooling and dry-sumps. They can also be fitted to wet-sump and semi-wet sump engines. The patented crankcase pumping action drives the breather. It normally purges blow-by vapour to ground, though it can recycle to the air intake. It usually comprises two purpose-designed valves, (but multi-valve arrays are also used). Engines run with reduced crankcase pressures, usually below atmospheric. By using opposed valve arrays with different flow-rates, more control can be exerted over the crankcase; as different crankcase breathing mechanisms come into play over the rpm range.  

The breather is designed to do three things: cut crankcase air pressure and oil leaks, actively pump blow-by vapour from the engine, and reduce power losses due windage, oil drag. It is designed to assist engine function, not impede it. 

  Fuels blended with 10% alcohol are replacing motorcycle-friendly fuels like 95 octane that often suited classic and modern bikes. Riders are used to racing bikes running methanol, and may be blasé at adding something similar to their fuel.  Yet it’s worth a closer look.  

This subject is complex, politicised and ‘on the move’. I focus on how it relates to crankcase breathing of classic, vintage and today’s motorcycles. Also I attempt to demystify it as far as possible, basing this article on the work of Prof Goodger, late of Newcastle Uni, and a long-time authority in this field.

   There are two main issues with ethanol and motorcycle crankcase breathing. First, any ethanol effects on bike crankcase and contents, and second any effects on crankcase breathing function. Perhaps the simplest way to attack it, is to ask…how does ethanol differ from the petrol (gas) used in our bikes?  

Two ethanol properties stand out for metal, rubber, fibre and plastic engine parts. 

1/ It attracts water- Ethanol attracts water far more than petrol. As blow-by vapour is mainly unburnt fuel, this increases the build-up of sump-water in bikes, especially those with poor breathing.   

With E10 there are now two sources of sump-water to consider. First the “combustion water” we’ve always dealt with... (think of the old rule…a gallon of water forms when a gallon of petrol burns.) Second any new ‘fuel water’ present in the fuel before it burns. This fuel-water varies every time we fill up. Moisture testing of fresh Shell 95 octane in my bikes shows 0.2-0.4% moisture. E10 will contain higher levels, depending on how it’s stored and transported, and how long you’ve had it in your bike. Once in your tank E10 absorbs moisture from the air, as the tank breathes and as condensation forms inside the tank overnight.

NB:- With E10, your tank should always be kept full between runs.

 NB:- E10 should never be mixed with petrol. This increases the chance of phase separation, covered below. Your tank should be drained if you change fuels. 

 NB:-As a rule of thumb approx. 0.5% water contamination in E10 fuel is a sign of engine problems, especially in winter and on days with high humidity.

     The E10 sump-water contents also varies from that with petrol. A different and corrosive chemical cocktail forms with the possibility of bugs growing as in diesel engines.

   Phase Separation (PS)- as moisture rises in E10 to approx 0.5% the fuel breaks down into layers. A bottom layer of alcohol, water, and some petrol forms. A top layer of depleted petrol is left. Neither layer forms a burnable fuel on its own, and bad starting and running follow. PS is more likely in winter, when smaller amounts of water trigger the breakdown, and on days with high humidity.

  2/ Ethanol is far more conductive electrically than petrol. At higher levels than E10, this allows galvanic corrosion to occur in engines, (similar to that in marine outboard engines). Partly for this reason, ethanol in high concentrations is incompatible with some metals particularly aluminium crankcases, barrels, heads and rocker boxes.  For classic and vintage bikes where crankcase conservation is critical, it seems sensible to limit engine exposure to ethanol, even at 10% levels. It’s no surprise racers using methanol, clean out their engines after every run.

Methanol is even more incompatible with aluminium, zinc, magnesium, copper, some solders, some rubbers, plastics and fibres.  Ethanol also has solvent effects on a range of metals, plastics and rubber used in our engines. These are related to the amount of ethanol present and the exposure time and temperature. E10 is less damaging than an E20 fuel and benign compared to an E85 fuel in classic bikes.

  These aspects are important but don’t directly affect crankcase breathing. What then does this all mean for crankcase breathing?

Conclusions:- The obvious conclusion from the above is with E10; we become more aware of moisture and water build-up in our engines. I’m not suggesting we need to drop all fluids after every run… but for classic bikes and modern bikes also; we clearly need to deal with the question of water build-up in our engines with E10.

 Countermeasures include e.g. avoiding short runs, using only fresh E10 fuel, avoid mixing fuels, keeping tank topped up, oil changes every 1000-2000kms, swapping breather components for E10-compatible materials, and ensuring our engines can evacuate a larger volume of water in the blow-by vapour passed out their breather.

 Where riders use E10, I suggest (where acceptable) purging breathers be used over recycling into the air intake. With ethanol fuels there will be more water. With this extra water come bugs and other new challenges for our engines. It makes even less sense to re-breathe this junk back into our engines, than it does with straight petrol (gasoline).  

 The Bunn Kit remains the only motorcycle breather designed to purge crankcases of sump-water by pumping it out, using otherwise wasted power under the pistons.     

The proud owner of this concours BSA A50 has made the most stringent effort to date, to achieve the optimal installation of his Bunn Breather Kit on a BSA twin. Over the past few months PM has experimented with several different breather installations, to achieve his desired result of cutting blowby and  oil ejection from his OEM timed breather.

The quality of his installations and in particular the placement and execution of his breather unions, are something I’m sure other riders will want to examine and follow. With PM’s kind permission, I attach several pics below showing his work with union placement.

One fascinating segment of the classic motorcycle scene is the classic "air-cooled" racing car community. This international movement locates, restores and races an eclectic collection of historic vehicles.  In Australia and New Zealand, they support an event calendar worthy of any classic rider's interest. They welcome riders wandering around their pits during regular track days and such days make wonderful classic club rides. Entry is also often free.

 Engines in these cars include the gamut of classic motorcycle marques e.g. Velocette, Vincent, Rudge, Triumph, Matchless, JAP and BSA etc.

Copy this address into your browser...

http://www.vhrr.com/newsletters/Loose-Fillings-Summer-Autumn-2008.pdf

It leads to a 2008 issue of "Loose Fillings" the Australian air-cooled racing car journal. Coincidentally this issue includes an article on crankcase breathing for these cars.

 After extensive testing with the Meriden 750cc Trident triple cylinder engine, I now believe the engine design prevents it from responding to the current generation of Bunn Breather Kits. This is the first vintage or classic engine I’ve come across, that does not suit my technology, (save a handful of early JAP engines). It’s worth reiterating what engines are proven with my Kits. I list them below... 

1/ All single cylinder, four-stroke, air-cooled engines, from all countries and periods.   (whether  over-head or side-valve.)  

2/ All 360 degree parallel twins. This includes virtually every classic British twin engine. 

3/ All V-twin classic and contemporary engines, overhead or side-valve. 

4/ All boxer engines of 2 and 4 cylinders, e.g. Douglas, BMW, VW. 

5/ Some multi-cylinder engines, of 4 cylinders or more e.g. Suzuki.  

The BSA 1960’s 750cc triple engine is perhaps the only significant engine I’ve come across in the last decade; where my current technology Kits fail to deliver a good result. After working through extended trials with noted Trident enthusiast GD, I believe the relative absence of  air displacement in these engines means it’s a class of engine requiring a fresh design of crankcase breather. This is most likely due to the unusual 120 degree crankshaft throws of this engine.  For example, as air displaces from one of the three barrels, there’s always another one or two nearby, available to accept the rush of air; hence there’s very little crankcase pumping effect. 

The Meriden (and Hinckley) answer to this breathing problem was to  connect a breather to the airbox and hope the intake tract hides it or deals with it. This is fine at some revs but not over the entire rpm range. It depends on the intake manifold air pressure and this varies with throttle opening. Blow-by builds up in the airbox on these engines, and fouls the intake tract,  just as it does on other British and American engine designs.  

Yesterday I started testing a completely new design of breather that will handle this engine, without the need to recycle blow-by into the airbox. It does not rely on the crankcase-pumping effect to evacuate the  sump.  We hope to have this ready for market in 2010. This design should suit the Hinckley Triumph triple engines as well. 

Meantime an earlier variant of my Kits, the ‘Blow-Bye Kit’ has been tried by several triples riders over the past five years, with some success. This Kit is a single-valve Kit and works in tandem with the OEM breather. A typical installation uses a union installed in the inlet rockerbox, as shown below. I emphasise this is not a complete solution, but has given relief in some cases. The 2010 generation Kits should  provide a complete solution.

As part of the classic motorcycle “industry mapping” work for my last book ‘Classic Motorcycling –A Guide for the 21^st Century’; I set out to answer the question…’How many classic motorcycles are there left on the planet?’.

 I undertook seminal research into surviving classic bikes around the world to answer this question. It’s important for long-term classic bike conservation, to have this kind of information available for governments, regulatory authorities, motorcycle industry lobby groups, and for all riders of classic and vintage motorcycles.  

This research involved a variety of surveys and econometric modelling and covered the UK, Australia, New Zealand and the USA.  By adding provisions for remaining countries and regions of the world, I conclude the surviving classic motorcycle population in the world is approx. 300,000 bikes. This figure relates to road motorcycles from all countries, manufactured between 1946-1979. It includes complete bikes in more-or-less running order. Scooters, competition and off-road bikes etc are excluded.

Thirty pages of this research are included in my book, available from either Panther Publishing in the UK or me. If you work in the motorcycle industry or as a consultant to governments or regulatory authorities; this is the most authoritative research available in this field. 

Contact me if you have need of this kind of research on rexbunn@bigpond.com  

There’s been a lot of comment in the media claiming classic motor vehicles lose value during recessions like the present one. This is usually based upon the writer attending one vehicle auction.

None of the ‘experts’ present any broader evidence to support their claims. My research shows vehicle auctions are an unreliable source of such information.  Certainly they give no insight into the international trends and changes in classic and vintage motorcycle values over time.

Here is the first hard evidence.  Over 2005-2006 I made the first long-term economic analysis on this question. My research covered classic motorcycles over the period 1981-2006, with value projections to 2010. The countries covered were the UK and Australia.

 In the research I constructed a classic motorcycle Consumer Price Index, the "Bonnie Index". This used the same approaches as government statisticians use in calculating a CPI or RPI index. 

 The findings for the UK were compelling, as shown in the chart below. The British "Bonnie Index" CPI (base 1981=100) reached 746 by 2006 in current terms and 331 in real terms. This means an average annual compounded growth increase in current prices of 26% pa, and 9.2% pa in real terms over 25 years.

Dry sump motorcycle engines with a scavenge oil pump and separate oil tank, generate a surprising amount of froth (foam) in the oiltank. Riders see this when removing the oil filler cap after a run. This can impact on engine function, service intervals and crankcase breathing.

Key points on Froth:-

1/ Oil froth varies by oil type, condition, temperature, pressure, flow, additives etc.

2/ Thicker oil tends to have more bubbles and they last longer, 10-20 minutes plus.

3/ Today’s oils often contain anti-foaming additives.

4/ Entrapped air in oil causes a pressure drop in the oil feed and scavenge pumps.

5/ The scavenge pump is designed to handle this. The feed pump often is not.

6/ Entrapped air in the feed pump line is serious. It drops feed pressure and cuts oil supply to bearings, leading to overheating and seizure.

7/ Entrapped air increases the oil volume and thus oil level. This can force froth out breathers and joints,  causing riders to think they have breather problems.

1/ Take a clean lidded, jam jar of say 375mls.

2/ Add  200ccs of new engine oil.

3/ Mark fluid level on jar (1). Shake hard for 2-5 minutes. Mark increased fluid level (2).

4/ Rest jar for a time matching oil circulation time of  engine.

NB:- For many this is 2-4 minutes (ex. Harley 900cc Evo oil capacity 3.4L. Pump capacity  1-2 L/min. Oil circulation time approx 2 minutes).

5/ Mark the drop in fluid level (3).

Hint:- Note the meniscus as you mark fluid levels.

6/ Calculate froth as (2) – (1). Calculate froth decay as (2)-(3).

1/ If the froth decay time exceeds oil circulation time…air may pump to your big end.

2/  Redo the test with used oil from your next oil change. You’ll find more, longer lasting  froth due the water and contaminants  therein….an argument for frequent oil changes.

3/ Check your current mineral oil with a synthetic or monograde and see the difference.

4/  Shine a light in your tank after a run. See the type and size of bubbles, how deep they are, and how long they last.

5/ Makers allow headroom in oiltanks for this reason, and for thermal expansion (see below).

6/ Makers take the oil feed from near the tank bottom to minimise foam in the feed. Oil return is pumped back into the headroom as it’s mostly froth at speed. A froth-tower is fitted at the top of the headspace, venting to air to release blow-by gas. If this blocks, your oil tank pressurises and the oil filler cap may leak or blow off.

7/ Harley-Davidson vent their tank headspace back to the timing case, a bizarre design that recycles blow-by into the engine. I routinely disconnect this vent-line.

8/ Frothing increases oxidation of our oil and cuts service life.

9/ Clearly if we reduce froth formation in the crankcase by better breathing, we improve engine lubrication. This is another reason to get crankcase breathing right.

10/ By creating a vacuum in the crankcase, some breather designs can reduce froth.

Fluids expand when heated and our engine oil is no exception. 3-6% expansion is usual. On a typical oil load of 3.4 litres, the expansion is 100-200ccs at operating temperature.

NB:- This is reason enough …never to check cold oil.

The joint effect of froth and thermal expansion increases oil volume by 10-15% or half a litre (quart) on many bikes.

This is one reason why over-filling is so common, and why it leads to breathing problems. As Phil Irving wrote years ago on a related oiling issue, there is a “pessimum” (cf. optimum) supply of oil to engine (bearings)…a point where supplying more or less oil, each improves engine function.    

  ENGINE FEEDBACK via Temperature Sensing -  Please read in conjunction with article 67/ below.     

This User Guide harks back to 2005 when I supplied a proprietary Kit to track oil temperatures. The Bunn Breather Kits became so popular I had to give up supplying these Kits, though I routinely install them on my own bikes, both classic and modern.

 1.0 Summary-We classic riders receive little or no feedback on fuel, temperature, oil pressure or electrical system status. Engine feedback wasn’t considered on most classic bikes, apart from a rev counter. The first symptom of a hot engine  problem can be  a seized piston. Apart from the $1000+ repair bill, you may have an off.  Monitoring engine temperature, using this kit, can warn you of a problem before that happens. It also enhances your classic riding involvement and hence satisfaction. I  developed this application  on BSA, Triumph and Harley-Davidson motorcycles, using a proprietary temperature gauge that’s proved suitable for classic air-cooled engines, over six years of application  trials. 

 2.0 Kit  Contents-   

2.1 The sealed Gauge Pack contains, the digital, removable gauge, gauge mount (adhesive), remote sensor, ~3 meter wire, battery 1.5V,L1142/186/LR43, and instructions.   

2.2 Temperature Sensing Data Sheet no.9.

3.0 Installation- Here’s a step-by-step guide:-  

3.1 Gauge-      

3.1.1 The simplest method is to mount the gauge on a fork top nut, using the included adhesive mount. (NB: clean the nut with metho). The adhesive foam tape handles normal  bike vibration. (NB: The gauge switches off under severe vibration).    

3.1.2 If you ride a single, or a bike with severe vibration, you can  use self-adhesive velcro tape, or self-adhesive foam rubber tape for greater insulation.    

3.1.3 For  permanent fixing, I suggest making up a bar or fork-mounted bracket, incorporating a sleeve and rubber grommet  mount. These are commonly sold for mounting e.g. tachos.     

3.1.4 If you want to avoid showing digital technology on your classic, I suggest a discreet mounting, down beside your headlight, where you can still see it on the road. If that still won’t do, then site it, out of sight, under your seat, or even inside the toolbox! 

3.2 Wiring-   

3.1.1  Run the wire along the frame tubes, from the gauge, to the sensor position  you’ve selected (see 3.3 below).    

3.1.2 Bundle the wire with other cables  for a tidy look.    

3.1.3 Ensure there is sufficient slack in the wire to turn the bars from lock-to-lock without strain or pinching. Avoid routing the cable too close to exhaust pipes. 

3.3 Remote Sensor-   

3.3.1 This can be  sited anywhere you choose on  the engine  casings,  oil lines, oil filter  or oil tank.     

3.3.2 Choose a site where the surface temperature doesn’t exceed 70C. (At 70C, the gauge switches itself off, to avoid damage, and will later resume).      

3.3.3 Secure the sensor in position, by cable-ties, an adhesive or  sealant fillet around the sides of the sensor, or with  adhesive foam tape. The sensor screw-eye is also useful.  

* Hint- I recommend taping it to the oil filter or oil tank,  beside the oil return line entry. This  ensures  measuring oil temperature as it leaves the engine.  I recommend using oil temperature as a key indicator of  engine  temperature, (given you can’t mount gauges on fins or exhaust pipes). For siting ideas, refer to your engine’s oil circulation diagram, and choose a spot close to a return line.                                                                   

* Hint- To force the sensor to measure oil temperature and prevent it detecting ambient air temperature, or  wind-chill;   enclose it in a  small piece of self-adhesive foam, ( door seal material or car sealing foam tape). Cut a hole out of the tape, roughly the size and shape of the sensor, and fit the sensor, into the hole. Cover the sensor in its hole, with another piece of tape. Stick the sensor, in your selected position. This should be out of sight, e.g. on the back of an oil filter, or underneath the oil tank. (If you want the absolute best mounting, smear heat-transfer paste  underneath the sensor, before you mount it). Gun adhesive or sealant over and around the tape mount  to prevent movement. 

4.0  Riding with the Temperature Gauge-  Assuming you mounted the gauge in one of the positions above,  it  monitors  several variables, viz:  

4.1 Firstly,  engine temperature  is monitored via oil temperature. Its surprising how engine temperature varies on a ride, and not just with speed. Variations of 25-30% are seen as you ride  through different patches of air. You quickly learn your engine’s normal temperature range  and  relate these to ambient conditions. A typical Summer range in Sydney, for a BSA single is 40-50C and Harley Sportsters 45-75C. Winter  temperatures’ range can be 25-50C. Generally, you’ll find your engine operating at 15-30C over ambient temperature. Obviously this climbs steeply and quickly at traffic lights or in parades. As an aside, the WWII Spitfire fighter was said to operate at ~40C. 

 4.2 Secondly,  abnormal changes  in engine temperature. If e.g. your gauge goes up past its normal range, after adjusting  the carburettor, you might  query  overheating from a lean mixture (or inadequate engine cooling).  If temperature  declines steadily, you might check oil pump function.               

 4.3 Thirdly,  the gauge shows your oil pump is working at  startup. If your oil pump has failed,  you’ve time to switch off, before your engine seizes. {As cold oil  enters the filter  or tank from the sump, the gauge drops for a short time, as cold oil displaces warmer air. Next , as warm oil  flows into the filter, readings climb  to normal operating temperature.} You'll never have to take the oil tank cap off again, to check your pump is pumping!   

4.4 The gauge also has a sensor in its main  housing. This measures air temperature and can be switched over, as you ride. ...useful if you’re wondering  why its so hot or cold  inside your helmet!  

4.5 The gauge includes a clock,  reminding  you  to stop  for a safety  break.   

5.0 Technical data-  

5.1 Removal- The gauge slides off its mount, for security. 

5.2 Temperature Range- The remote sensor  range is -50C to +70C.                                                 The inbuilt sensor range is -10C to +50C.   5.3 Accuracy- +/-1C. 

5.4 Battery 1.5V.  Type  L1142/186/LR43. 

5.5 Application testing was performed on air-cooled engines. The kit has not been tested on water-cooled engines, but should work, providing coolant  doesn’t exceed 70C.  

Disclaimer- As user installation and operation vary widely, I do not warrant the kit will work on every make and model of classic motorcycle. Contact me for advice if you have an installation outside the above guidelines, at  rexbunn@bigpond.com 

  This last Northern hemisphere Winter was severe. Writing from Australasia, it seems odd writing about such conditions. However, these  place extra load on crankcase breathing. A number of UK/EU riders asked for advice in resolving issues with breathing. As often the case, an engine condition shows in the engine breather. The cause is not a breathing problem. Instead, the breather communicates an underlying problem.  

This 2008-9  Winter, engine breathers [including some Bunns] started to vent blow-by emulsion. Why was this? After liaising with several riders having similar problems in different countries, I’m confident we understand the causes, and have  developed DIY solutions for all air-cooled (and water-cooled) motorcycle engines, whether vintage, classic or contemporary. 

 The Causes- The underlying cause is... engines aren’t reaching normal operating temperature and/or are not held there long enough to vent sump moisture.  

NB:- Unlike car engines, bike air-cooled engines don’t operate at constant temperature. Our engine temperatures range up or down depending on ambient  conditions. Normally they’re about 15-30C above air temperature.  The problem is acute with engines using plenum chambers for breathing e.g. Royal Enfield and Harley-Davidson, and bikes using re-cycling breathers, i.e.  most contemporary bikes.  

The causes include... engines ridden in low temperatures, ridden frequently, ridden at low speeds, ridden for short runs, ridden with maximum oil load, and bikes with infrequent oil changes. The problem is acute in bikes where crankcase breathing is compromised to start with. This includes Royal Enfield singles, some Harley-Davidsons and classics with separate oil tanks, and bikes with worn or malfunctioning oil scavenge pumps. An oil pump marginal in Summer will be found wanting come Winter. 

Bikes with Bunn Kits are not immune. The Bunn installation actively pumps out blow-by vapour vs the passive release of gases from other types of breather. It can vapourise and pump 2-5mls of sumpwater per km, and starts vapourising moisture soon after startup. If  an engine has 20-50mls of sumpwater, the Bunn Kit requires 25-40kms to purge that moisture, more or less depending on ambient and riding conditions. Less can lead to blow-by condensing in the lines.  

The Symptoms- White blow-by emulsion condensing in  breather tubes, valves and air-boxes.  Normal bike engine sounds may alter, becoming louder. The engine loses “pep”. Something is not right down there. 

The Solutions- These start with the obvious...avoid short runs in Winter.  If the bike is a ‘ride to work’ bike, this is impractical, unless the rider takes a long way round to work. Solutions include:-

1/ Avoid short runs in Winter, or at any time.

2/ Lower circulating oil volume to reduce the “come-up” time to temperature.

3/ Increase oil changes to 1,000-1,500km intervals.

 4/ Ride in lower gears, to again reduce the “come-up” time to temperature.

5/ Idle your engine before starting off... with a hand on rockerbox till it warms.

6/ Accelerate the “come-up” time, by reducing engine wind-chill. This approach was common  in earlier days on water-cooled car engines. A sack or louvre might be draped over the radiator in Winter.  The approach has much to commend it on bikes but with air-cooled engines, we must be vigilant to avoid over-heating the engine. A DIY approach is discussed below. This uses a deflector plus oil temperature gauge to manage Winter engine temperatures.   

A DIY Airstream Deflector- The concept is simply to reduce air flow over the engine cooling fins.  A  e.g. circular deflector plate of up to 150mm diameter can be mounted on the down-tube in front of the engine barrel, using a U-clamp. There are two schools of thought on  airstreams. Bell  argues for unobstructed  airflow while Robinson argues turbulent air gives more fin-cooling, as the air stays  longer in contact with fins, and more heat transfers. In our case we want to deflect air flow. Other approaches include e.g. a Harley-type nose-cone or a bash-plate to insulate wet-sump or oiltank-in-unit engines.  As well, engines can be pre-warmed with an electric blanket and oils can be pre-warmed with an immersion heater.

As engines respond differently, we MUST have temperature feedback. If you have an oil or engine temperature gauge already, fine. If not, a DIY User Guide is reprinted above in article 68/ 'ENGINE FEEDBACK via Temperature Sensing',  in the public interest.     

  23 Royal Enfield FAQs for Electra,Classic, de Luxe 

Background… Many Enfield clients have appreciated these FAQs over recent years, Finally I get around to blogging them. Crankcase breathing has been a neglected subject since the birth of the motorcycle.  My company has focussed research on this subject for the past decade, patenting and  introducing new solutions for old breathing problems e.g. oil leaks. We appear to be the only researchers patenting new breathing technologies for classic and vintage motorcycles around the world.

                  The original British Royal Enfield bullet engine has been developed in the Indian plant and this impacts its crankcase breathing. The OEM breather stifles engine breathing and leads to sumpwater, power loss, oil and blow-by emulsion leaks. The canister and breather tubes can be replaced with the a Bunn Breather, and the problems corrected by purging the blow-by vapour to ground where acceptable or recycling it. This FAQ sheet should be read in conjunction with Blog article 41/  Royal Enfield-  Reviewing Crankcase Research 

                         Frequently Asked Questions…

 1/ Why are there so many OEM breather lines on the Bullets especially the Electra?- The Electra designers tried a semi-closed recycling breathing system, possibly to gain emission compliance. I think this is why they plugged the British barrel union, drilled compartments, and linked oil tank, timing chest, chaincase and airbox with the canister. These connected compartments act as a series of plenum/surge chambers.  Forcing corrosive blow-by into the chaincase where it corrodes the chain, the oil tank where it denatures the oil, and over the rear chain which  it corrodes…doesn’t make sense to me. Far better to remove it from the engine.

 2/ Must I remove the OEM breather to fit the Bunn Breather? - The OEM timing case and oiltank tubes are removed, along with the Electra canister to make room for the Bunn air filter. The chaincase and aircleaner tubes on the Electra can be left, with the latter plugged. The canister can be left on the Classic. 

3/ How Does the Bunn Breather Operate?- The Bunn Breather lowers crankcase air pressure and meters air flow through the engine. It cuts oil leaks, pumps out blow-by to cut engine wear, and cuts power losses under the piston and due to oil drag. It creates a unidirectional airflow through the engine assisting blow-by management. Our approach is to vent blow-by vapour before it can condense into blow-by emulsion, the so-called “elephant snot’ familiar to the Royal Enfield community.  

4/ Is it simple to install?- Yes.

 5/ Does it require much maintenance?- No  

6/ Is it Installed Correctly?- A ‘Blow Test’ confirms this, i.e. blow down the Bunn Inlet line and feel air passing out the Exhaust line.  

7/ What Kind of Material Comes Out  Crankcase  Breathers?- Four kinds of materials come into and out of any breather at different times. Knowing these help diagnose engine function. The four materials are:- 

7.1  Sumpwater- seen as water, steam, white smoke  or moisture. Expect heavy moisture on first runs with the Bunn Breather, and briefly on most runs thereafter, for 1-5kms. The Bunn Breather’s patented pumping action empties 2-5mls of sumpwater per km. On a Bullet with poor breathing, 50mls+  water accumulates with the OEM breather…it can take the Bunn 40-100kms to  pump out that sumpwater from the case, one reason not to take short runs.

7.2  Blow-by- seen as a cloudy gas or more commonly a brown-stained watery fluid that becomes oilier as the fuel and water in it evaporate. It’s often confused with engine oil. Expect to see a drop of this after a run, round the  Bunn Exhaust breather. Blow-by forms each time the engine is run, and this process continues after you switch off, hence a drop condenses at the valve outlet overnight.

7.3  Blow-by Emulsion- seen as a white fluid in breather lines. The sumpwater and unburnt fuel in the blow-by combine with other constituents to form an emulsion. In the Bullet canister this dries into offensive white grease that blocks the OEM breather and migrates into the aircleaner, dripping onto the Electra silencer. The OEM breather tubes and duckbills  encourage this by restricting air flow.

7.4  Engine oil- seen e.g. as oil globules flinging up a breather from e.g. flywheel spray. With the Bunn Breather, oil may be seen in the Inlet line at idle in the Classic model, and at high speeds with the Electra. It pumps back into the timing chest when engine speed changes. In the Bunn Exhaust line, oil froth enters a short way until it reaches the primary and secondary baffles. It is not normally seen above the baffles.

8/ How do you tell the Difference Between Blow-by and Oil in the Breather?- Blow-by is mostly unburnt fuel, moisture, ash, soot, and acidic sulphur and nitric compounds.  If you are careful, you can test fresh blow-by fluid by rubbing it on the fingers [and then washing hands].

 Caution:- Tasting blow-by shows it’s a toxic, acidic, corrosive oily fluid that chemically burns the tongue. I do not recommend tasting it.  Unburnt fuel and water evaporates, concentrating thefluid, so it becomes oily. After a day riders may swear its oil. It isn’t SAE20-50  engine oil [compare with a drop  on another finger]… but a  lower viscosity ~SAE5-10, with a watery, skinny feel. If it feels like that, you’re dealing with blow-by fluid, that contains a trace of light, volatile fractions in engine oil, carried out with unburnt fuel, water, ash, soot, sulphur and nitric compounds. That fluid is “…nasty, noxious, corrosive stuff…” to quote Peter Williams.  

9/ Should Oil rise along the Timing Chest breather line?- It is typical for oil to rise a short distance along this line at high speeds in the Electra, especially  if the timing chest duckbill is removed. In the Classic it is seen here at idle. The Bunn Breather uniquely pumps this oil back into the chest as speeds change. The causes include the proximity of timing chest oil return holes to breather drillings and oil/air return volumes from the uprated pump. NB:- This is also a typical sign of an overfull oil tank, common on the Enfields. 

10/ Should Oil rise up the Oiltank Breather Line?-  Oil should not rise far up the oiltank line, only as far as the primary baffle of the Bunn  Breather Kit. The most common cause is an overflowing  oiltank... there is too-little headroom. The Indian designers try to use this headroom as a surge tank but provide no froth-tower... a design doomed to fail.  The headroom is shrunk by sumpwater, foaming oil return and overfilling, so the oiltank levelreaches the tank union and on hill slops up the union.  

11/ Engine Oil Level - Check engine oil ONLY after dismounting the  bike with a hot engine. With hot oil the R/E dipstick is hard to read. Screwing in the dipstick, as per manual makes it even harder to read.

  Oil Check Tip: Insert the dipstick till  it rests on the tank spout, then withdraw for a more accurate reading. Add a finger width to allow for filler  thread depth. The oil level at the top groove is the maximum. The Electra wet-sumps faster than other classics. An hour sees the level drop and riders over-fill as a result. Sumpwater increases the oil level with OEM breathing. Storing the bike with piston at TDC can slow wet-sumping.

 12/ Does  Dropping the  Oil  level reduce oil spitting up the Breather?- Yes it does. Dealers suggest running the oil level ONE CM  below the dipstick mark. More than this  reduces circulating oil volume and engine cooling. I suggest If you drop it, fit an  external oil filter to restore circulating volume. It’s better to treat the causes with a Bunn Breather.

 13/ Should Oil be Dripping from Exhaust or Chaincase Line?- On the first few runs with the Bunn Breather, old blow-by emulsion can heat up and  drip from the chaincase breather line, behind the gearbox. On these first runs we are normalising engine breathing: the engine is jettisoning accumulated blow-by and sumpwater, so a few drips may be noted initially. 

14/ Should lots of  Condensation be seen in the Bunn Exhaust line?- Yes. Riders should expect to see a lot of steam, moisture and condensation in this line for the first few runs, while the breather purges built-up sumpwater and blow-by from the engine. Most of this is pumped out as steam, but some condenses around the valve  as a watery brown fluid on early runs.  

15/ I noticed a few drops of what looks like oil on the floor overnight?-You expect to have a drop of brown blow-by fluid collecting at the Exhaust valve, when  blow-by vapour meets the atmosphere. With the hot Bullet engine at 150C and oiltank at 75C…the  evaporation process carries on after you stop. The vapour rises up the line from the engine and over hours collects into a few drops, which find their way out the valve onto your floor. After a few days this tapers off.  

16/ Why are there twin baffles in the Bunn Breather?- To replace the missing froth-tower. The Primary baffle handles oil spitting up the line from that brimming oil-tank below it. It also helps act as a flame-barrier, if you decide to try recycling blow-by. I do not recommend this, as the crankcase, timing case and oiltank at times may be flammable, given the new drillings. The secondary baffle traps oil droplets that kick past the primary baffle, and returns them to the tank, when rpm lowers.

 17/ Why Must we check the Oil level After Each early Run with the Bunn Breather?-The oil level can go down on early runs, as sumpwater is vapourised and purged from the engine.  [This doesn’t mean the Bunn Breather is  burning oil]. Oil may need topping up, but avoid over-filling as oiltank headroom is minimal. 

18/ There’s not much air coming out my Bunn Breather, is this normal?-  Yes. A common misconception is more airflow is better. More crankcase airflow means more lost power as the piston pushes air around. A 500cc piston does ~130ft/lbs work along its stroke as it displaces air, unless a Bunn Breather is fitted. The Bunn takes control of the crankcase airflow and allows sufficient air through to dilute blowby and pump it out of the engine, and no more.

 19/ Why does air only come out any open breather, when the engine ‘suck and blow’ should cause it to rush in and out?- It’s a sensory trap. The skin sensors report air rushing over the finger as air rushing out, even if it’s  sucking and blowing. Try this with a wet finger over a vacuum cleaner. You’ll swear air is rushing out of the wand!  

20/ I’ve a white fluid collecting in a breather line?- This is blow-by emulsion. In the OEM breather it’s unavoidable. It should not be seen with the Bunn Breather, unless e.g. the installation forms a “P-trap” in an exhaust breather line. A P-trap can allow blow-by to condense and form a fluid level that may block the tube. Avoid P-traps in breather lines. They are found in household plumbing systems to block air flow.

 21/ Is there a Minimum Run Duration with the Enfield?- Yes there is. The engine design and Indian mods render it susceptible to crankcase moisture. I recommend a minimum run of 40-80-120 kms if possible. The logic is to get the engine up to operating temperature and keep it there long enough for the Bunn Kit to pump out the moisture. (My Kits only work with engine running). If you ride only 10-20-30kms, especially in Winter, you handicap the Bunn Kit in ridding your engine of moisture. Blow-by emulsion may reoccur. If you must do daily short runs, try and do one 100km run each week. Also  increase oil changes  to 1000 mile intervals. These steps enable the Bunn Kit to do it’s job and help prevent the return of emulsion. 

  22/ How Does the Bunn Breather handle very worn engines?- The Breather system is designed to cover a wide range of engine build-states and wear and tear. Clearly as engines wear, rings no longer seal against the piston and blow-by increases. In engines with advanced cylinder and ring wear, blow-by can  become so great as to undermine the Inlet breather role. Normally before this stage, the rider has re-bored/ re-ringed the engine.  Where wear reaches this end stage, cranking pressure reduces to 100psi or less. Normally Electra engines operate at 140-150psi. Of course low cranking pressure is also seen on new engines.

 23/ My exhaust note seems to have changed after fitting the Bunn Breather?- When riders first reported this, I regarded it as a side-effect of changing crankcase air pressure. After many instances and dyno trials, it’s clear the Bunn Breather reduces power losses below the piston, and oil drag. Rider’s reports are observations of a small power increase. Other reports of e.g. idle increase, reduced engine braking, a more willing engine etc corroborate this.

Bunn DIY Motorcycle ‘Dehumidifier Kit’ - User Guide

 This is the User Guide for the 'Dehumidifier Kit  described in Blog articles 24/ and 46/ below. I make this information available to  existing clients and all riders in the public interest.

1.0 Introduction:  Moisture in the motorcycle engine is often cited as the single greatest, preventable cause of wear. Blog articles 24 & 46 advise on the causes and prevention of moisture and sumpwater, using the Bunn Breather Kit. However a lot of moisture develops in the engine between runs and when the bike is stored.  Sumpwater often begins on a day with high humidity. Today in my garage the relative humidity is 79%, temperature 16C, barometric pressure 712mmHg, and dew point 13C. The dew point is the temperature where moisture condenses out of the air, as the air cools.

If the temperature falls 3C tonight, which it will: and other variables were to stay much the same…moisture will condense out inside my crankcase. It’ll condense on the walls and roof of the crankcase, and under my pistons. It’ll run down, washing the protective oil film off barrels, down over my mains and big ends, taking their oil film with it. Corrosion will start by morning. The water flows into the sump oil and forms a layer beneath it. In the morning the air warms up, and stops condensing. Tomorrow night, if conditions are right…the process starts over again.  

2.0 Preventive Action: What can we do about it? The obvious answer is ride our bikes every day 50-100kms, to get and keep them hot to vapourise the sumpwater that builds up in storage. For most classic and vintage bikes that doesn’t happen. Nor for most new bikes as they’re recreational vehicles, used at weekends. Most bikes spend their life in the garage.   To beat moisture and sumpwater, we have to prevent it in the garage, not just on the road. An effective way is to connect a dehumidifier to your engine, in between rides. This prevents condensation, and reduces engine wear due corrosion and metal-to metal wear. A motorcycle dehumidifier to fit the Bunn Breather can be easily constructed and costs little to operate. 

3.0 Bunn Dehumidifier Kit Contents:  Purchase the following materials from an aquarium shop and supermarket. The total cost should be about $A25, USD20,  GBP10:- 

3.1 One aquarium air pump e.g. Aqua One 2500.  

3.2 One ‘Air Stone’ filter, approx 50mm long. 

3.3 Two zip-lock household plastic bags, approx 250mm by 200mm.  

3.4 One pack of household ‘Moisture Absorber’ approx 450gm. 

3.5 Short lengths of 5mmID and 8mmID tube, rubber or PVC. 

3.6. Packaging Tape, rubber bands and scissors. 

4.0 Kit Assembly:  [Estimated assembly time 5-15 minutes.]

4.1 Remove the Moisture Absorber foil seal, leaving the  paper filter in place.

4.2 Insert the Moisture Absorber pack in the Zip-Lock bag, keeping it upright, as it’ll fill with salt water.

4.3 Insert the Air Stone into the 5mm ID tube, and place it into the bag, resting on the Absorber pack.

4.4. Insert the 8mmID tube end into the bag head-space and seal the zip.

4.5 Seal the end of the bag and the tube entries with rubber bands and packaging tape, to avoid air leaks.

4.6 Connect the 5mm tube free end to the air pump.

4.7 Place the second  plastic bag over the Bunn air filter, sealing with a rubber band, for easy removal.

4.8 Puncture the bag and Insert the 8mm tube into it, sealing the entry with rubber band and tape. .

4.9 Ensure the tube ends inside the bags are clear…and switch on the pump. 

5.0 Using the Bunn Dehumidifier Kit:  

5.1 Connect the Kit as soon as you return from a ride. Moisture is at a maximum then, and during the  first night after a ride. The Bunn Breather and Dehumidifier Kits work together to continuously protect your engine.

5.2 Leave the Kit connected and operating between rides, and when the bike is in winter storage.       NB: - Be sure to comply with the air pump manufacturer’s instructions on pump operation.

5.3 Depending on your local humidity and how your engine develops moisture, the Moisture Absorber pack should last weeks or months. Follow the maker’s instructions on when to change it, and on disposal.

5.4 This Kit is designed for use with the Bunn Breather. It must be connected to the Bunn Inlet breather union, never the Bunn Exhaust. If in doubt, do a “Blow-Test” to prove an open airway.

5.5 The Air Stone acts as an extra  filter to prevent dirt or absorber particles entering into the engine.  

6.0 Hints and Tips:   

6.1 Many materials can be used as desiccants i.e. dehumidifying agents. Silica Gel is one; common salt [sodium chloride] is another. Calcium chloride is often used in household desiccants. Rice is also used. See a list at

http://www.mallbaker.com/techlib/documents/americas/3045.html   

6.2 Calcium chloride is popular in supermarket products. It’s food-grade and is similar to table salt, so avoid spilling any water [which normally collects in the Absorber pack], onto your engine.

6.3 Keep your air tubes away from the fluid which collects in the Moisture Absorber pack.

6.4. If using methanol fuel, consider using another desiccant from the list above.

6.5 If your Moisture Absorber pack has no paper filter, insert the Air Stone into the 8mmID tube, to prevent any particles from the Absorber pack, being drawn into the engine, as calcium salt corrodes.

6.6. The Bunn air filters are tested to filter CaCl2 particles down to 5-2 microns. Still I recommend using both air-stone and Bunn filter, and avoiding movement of the desiccant pack while in operation, to prevent  migration of desiccant particles through the engine.

6.7 Observe the Moisture Absorber manufacturers directions on disposal, when it is exhausted.  

6.8 Clearly  a more elegant and permanent installation can be developed by riders. This Kit provides an entry-level approach to suit the least-skilled rider.     

  Disclaimer- This information is given in good faith. As user installation and operation vary widely; I do not warrant the Bunn Dehumidifier Kit will work on every make and model of motorcycle.  Nor do I warrant its use with breathers other than the Bunn Breather range. Riders using this Dehumidifier Kit do so at their own risk.

As the number of classic bikes in original condition declines, more bikes have engine mods to ignition, cams, pistons etc. On some modified bikes, perhaps many of them; the factory  ‘timed breather’ needs to be modified as a result of the engine mods.   

Timed breathers are found on many classic British and American bikes. There are two main British types- “Shaft-Bush” breathers and “Disc-Valve” breathers. Disc-valve breathers are found on Norton and BSA twins and BSA singles. Shaft-Bush breathers are found e.g.  on later BSA singles. Harley-Davidson has a double-acting timed valve breather. We’ll look at this in another article.   

The breather design is it’s undoing. Such breathers were often  installed on the left  end of the camshaft, with cams in the middle and points on the right. They  aren’t adjustable. They open and close on piston downstrokes, venting a tiny amount of blow-by gas. The timed breather is good at cutting return flow, but no good at passing air volumes. On a “Shaft-Bush”  breather a bush drilling is 3/16”, and the circumference 3/4". The holes match up for 8% of shaft rotation, and are fully open for half that... not much air passes.

British designers were reticent on their timing. Disc-valve breathers may open for  less than 10 degrees. This is often just before BDC, so crankcase pressure builds up for most of the downstrokes, as if there was a blocked crankcase: causing severe pressure spikes. They operate in fixed relationship to the cams. They open and close abruptly, regardless of the pressure gradient across them. This is another reason for the severe pressure swings you find with these breathers.

 Problem no. 1- When cams of different grind are installed, breather  timing is unchanged. It  may no longer match valve opening and closing. This cuts breather efficacy and leads to increased crankcase pressure and oil leaks.  

Quick Check- Do a “blow-test’ with a valve timing device, to see if your timed breather still opens on downstrokes, and by how much.  

Solutions- If flow is meagre or obstructed, remove the breather and install an in-line system like a Bunn Kit. To save an engine strip, block the  breather union and install a Bunn Kit using other unions.  

As we move further along the camshaft from left to right, the next assembly is the ignition timing device; either a set of points or a Hall effect sensor for electronic ignition. This assembly is adjustable, to match ignition timing to valve operation. This leads to the second timed breather problem.  

Problem no. 2- As more classic bikes fit electronic ignitions, the timed breather can lose timing accuracy. One reason is the higher engine speed to time electronic ignitions vs OEM points ignition. For example a Boyer ignition is timed for full advance at 5000rpm vs 3000-4000rpm full advance specified by the bike maker. Such bikes spend their time running with a retarded spark, and engine temperatures and performance can fall off. A timed breather may be handicapped by reduced flow, increasing case pressure and swings in pressure, as it’s opening interval no longer matches peak gas pressures and flows. 

 If the bike is timed at 3000rpm, it may run with excessive advance, more power, higher engine temperature and combustion pressures and  perhaps knocking. Blow-by volumes will spike as a result. The breather timing again may not be ideal,  and case pressures rise and swing wildly. Oil leaks from joints and the breather follow.  

In bikes with both different cams and electronic ignition, the chances for bad breathing multiply. With the different burn behaviour of today’s fuels, the chances increase further. If a high compression piston and a bigger carby have also been added, the chances for bad breathing further multiply.  

What is required is an engine breather that adapts to these changes in engine performance from altered valve and ignition timing. This requires what I term “Demand Breathing” and the Bunn Breather typifies this approach. Whatever the valve or ignition timing, my kits continue metering air in and pumping out blow-by. 

Caution- Up to now I’ve often advised clients to fit Bunn Breathers in tandem with OEM timed breathers, on the basis they operated more or less synergistically. This advice no longer applies to bikes with engine mods, and especially bikes with altered ignition and/or camshafts.  I see now my Kits can be hindered by a malfunctioning timed breather. These kick up violent pressure swings in the crankcase, even when operating normally. Looking back over the last 1000 bikes, I can think of a number of bikes, manifesting this problem. Two clients recently fell into this category. One corrected the oil venting his BSA timed breather by altering his ignition curve, and the other Moto-Guzzi, though not having a timed breather is also changing his ignition curve. 

Conclusion:- There is a risk altered valve and/or ignition timing in bikes with timed breathers, causes breathing problems, oil venting etc.  I recommend checking and if necessary blocking such timed breathers, during a Bunn Kit installation, in modified bikes. We are continuing research into this area to chart actual blow-by flows under varying engine conditions. I’ll post these results later in the year.  

David’s 1954 BSA B33 500cc installation of the Bunn Breather is quite simply the best BSA single example to date. His painstaking attention to detail and  step-by-step testing, mark this as one of the top five Bunn  Breather installations ever. It of course helps he’s a hydraulic engineer.

In the first pic below is David’s placement of the Bunn Inlet breather. The filter/valve assembly is nicely placed behind the barrel in relatively still air. It leads down to a union on the OEM right-side case breather.

In the second pic below is David’s Exhaust breather union design. Stylish and damned near invisible.

Several clients ask about using valves sourced from  HHO (Hydroxy fuel) equipment  vendors on EBay etc. These HHO valves are used as non-return water stop valves and flame-stops. They are  made from plastics with rubber seals. After evaluating several of these valves, I suggest riders browse my Blog article 26/ below, before entrusting your bike to  these valves.  While these valves can be connected to motorcycle breather lines, how effective they are depends on testing each design. The type two of my clients considered are made from translucent polypropylene, with a Viton rubber floating seal. The valve casing  is pan-shaped with single barbs.  Let’s compare the HHO valve design against key performance requirements... 

1. Must open and close at low pressures- The HHO valve is advertised  with a cracking pressure of 26mmHg. By contrast my valves are designed for 0.5mmHg. There’s far too much inertia in the HHO valve for efficient crankcase breathing. 

2. Must handle low flows- The HHO valves don’t provide flow data. Given their design, I believe they flow a lot less than my valves.  For example their design gives a high resistance coefficient. I estimate this at 0.5-0.7. By contrast I design  for a resistance coefficient of 0.1-0.2. As flow resistance increases, it makes valves more susceptible to condensation and blocking.

Up till now, riders have lacked technical guidance on how to place their engine breathers. Any place on the crankcase or timing case was seen as much the same as any other place.  Decisions were based on ‘cosmetic’ aspects for concours bikes, and ‘convenience’, using existing unions or the easiest place. We can lay down some ground rules for breather union placement on motorcycle engines. These are based on the expanding knowledge of pressure states in engine compartments, and the impact these have on engine operation. From Bell’s writings, my own and others, we can start to install breather unions based on science vs guesswork.  This first approach is based upon areas in the engine where crankcase air pressure varies. There are areas of relatively high pressure and those with generally lower air pressures. For the moment, I’m setting aside the pressure displacement from piston movement in singles and 360 degree twins. Instead we’re looking at the underlying pressures at different airspaces in the engine. 

  Low Pressure Areas- These include air-spaces close to engine components that are moving at high speeds. Examples include the flywheel rim, conrods and pistons etc. These areas are identified courtesy of Dr. Bernoulli i.e. crudely, as speed increases, pressure falls. 

High Pressure Area- These include air spaces which have no fast moving engine components or any other factor leading to a reduction in air pressure e.g. a draft tube, one-way valve etc. An example might be the central area of the rockerbox, say close to the OIF breather union on later Bonnevilles.  

Rule One-We should try and install Exhaust valves in compartments or crankcase spaces with generally higher pressure. The logic is we want to reduce crankcase pressure below atmospheric pressure. Installing breather unions in high pressure spaces will help us lower overall pressures in the engine compartments. Examples of such compartments include rocker and cam boxes and regions in the crankcase distant from the flywheel and scavenge pump intake.

 Rule Two- We should try and install Bunn Inlet breathers in compartments and spaces where air pressure is generally lower. This will encourage inward airflow and efficient flushing of blow-by vapour through the engine, (though it may impact on reaching the target crankcase vacuum in some engines). It can be a trade-off between vacuum (and associated power gain); and engine conservation (by purging blow-by vapour).   

Given Bunn valves control both air inflow and outflow volume, pressure and flow objectives can be met in this way. Examples include air spaces close to the periphery of the flywheel and around the barrel close to conrods and pistons. The classic example of such a space is the timing plug drilling, which on e.g. Triumphs and BSAs penetrates close to the flywheel rim. This is perhaps the lowest pressure region in any engine. In those engines which link the primary chaincase and crankcase e.g. post-1970 Triumphs, suitable low pressure regions may be obtained with a union close to the alternator rotor or mainshaft sprocket.  

Putting these two rules together, gives riders a logical basis for deciding among the usual four installation options with Bunn Breathers. These options are Top>>Down, Bottom>>Up, Top>>Top and Bottom>>Bottom installations.  For example, on later Triumph and BSA singles, twins and triples, the use of the timing drilling…in a low pressure region, favours a Bottom>>Up installation. This takes advantage of the low pressure flywheel rim region is two ways. First it encourages air entry across the pressure gradient from atmospheric pressure outside, into the low pressure adjacent to the flywheel. Second, flushing air at atmospheric pressure into the low-pressure air stream around the flywheel, helps disrupt the low pressure causing oil drag on the flywheel and power loss. The Exhaust valve is fitted to the relatively high pressure rockerbox.

 With Dr Bernoulli guiding us, we can now analyse our engine compartments, identifying high and low pressure areas, and so place our breather unions sensibly, to achieve optimal breathing for our bikes.  Doubtless we’ll uncover more decision rules as research continues.  

 Tuners report blow-by is greatest at idle (and at WOT). They speculate about piston ring flutter and possible causes.  My research agrees blow-by is greatest at idle. There’s no hard evidence as to exactly how blow-by forms. Clearly it’s unburnt fuel vapour escaping past the rings down into the crankcase. When this happens is less clear. Ring flutter occurs when the ring rises off the piston land, allowing air to flow around it, between ring and piston… though some passes through the ring gap and spaces where the ring-barrel gap is greatest. The piston ring is then,  another floating seal.

Commonsense suggests this happens on the combustion stroke when cylinder pressure is greatest. On the other hand, chamber pressures rise well before TDC on the combustions stroke. As piston rings are very light with a relatively large, exposed surface area; it’s likely peak combustion pressure at TDC forces them onto their best seal against the piston land during this stroke. I cannot see a way to test this.

Nor does it really matter if, as I suspect, much bike blow-by occurs on the induction stroke. The pressure gradient across the piston is much less then, and rings are more able to float off the piston lands at TDC, when the piston changes direction. This may explain why so much unburnt fuel vapour ends up in the crankcase…there’s more of this about on the induction stroke, than on the combustion stroke.

Till 1962, US vehicles breathed via a “draft tube”, an open breather to the rear crankcase. (Russell. “PCV…real advance or just another headache for the motorist. Mechanix Illustrated, 5/1964 pp 118-124.) It’s important to note back then, engineers were divided over PCV breathers. Many saw PCV breathing as a backward step. For motorcycles I believe that is still true.

        An uprated 2009 version “draft-tube” coupled with a Bunn Breather, gives a rider another option in managing his crankcase. I’ve done a lot of bench and road testing on draft tubes, and this year build them into Bunn Kits.

        They allow riders to further reduce their crankcase operating pressure. This is of interest to riders with performance engines, where driving down crankcase pressure cuts oil drag, and boosts power.  Classic riders with oil leaks also benefit from a little less pressure. The only group of riders who should never fit a draft –tube are those riding in very low temperatures. Otherwise, I believe all riders benefit from this breather addition. 

 To install a Draft Tube with a Bunn Breather, here's a step-by-step guide...

1/ First  form the draft tube by cutting a 4-6" length of 10mm ID rubber tube.

2/  Next  "slash-cut" one end at a 45 degree angle. See Blog 49/ pic.

3/ Insert the tube over your Bunn Exhaust valve.

4/ The 45 degree hole in the tube end MUST face the rear of the bike, i.e. away from the airflow.

5/ The slash-cut itself MUST be perpendicular to ground, i.e. at 90 degrees to air flow. The tube will then be angled back to line up the slash-cut. If the angle is incorrect, you will receive no benefit.

6/ The tube MUST project down under the bike frame, say behind the gearbox. Take it down to roughly the level of the lowest frame section e.g. the prop stand mount on a Harley-Davidson. The slash-cut end must project into the airstream under the bike. If it's left inside the boundary layer i.e. close to frame under the bike, it will not work. Direct it to one side or the other, away from the tyre.

With a Bunn Breather and a Draft Tube, you achieve a lower crankcase pressure at speeds above 60kmh. This translates into reduced power losses as speed increases.

Interestingly, I noted a draft tube on a Michele Alboreto Ferrari F1/86 racecar at the Creek last week. If Ferrari is still using draft tubes on F1 cars, they clearly offer advantage. See pic below.

Crankcase breather R&D is like a jig-saw. Given enough time and  research, the pieces form a picture of what goes on inside our engines.

This article summarises 2008-2009 road and bench trials using the Harley-Davidson Evolution quad-cam 883cc engine, fitted with Bunn Breather. The findings relate also to single camshaft forms of this engine, other V2 engines and to an extent; every four-stroke dry-sump air-cooled engine.

This research was suggested by David White, and owes a great deal to his wise counsel. It was undertaken in Australia and New Zealand on stock engines fitted with Bunn Breathers, together with test-rigs. Pressure, temperature, sight and flow gauges were fitted to engines and frames. Measurements were taken at rest and at speed on the road, and under different riding conditions e.g. on steep hills. Trials included the use of draft tubes. These enhance crankcases vacuum by up to 6%.

The findings are summarised in this article. The raw data are on file. In this article, ‘blow-by’ refers to crankcase gas generated by unburnt fuel vapour escaping past pistons, during combustion and/or induction strokes. 

Key Finding- Different breathing processes occur in engines under different conditions. It is no longer meaningful to talk about ‘crankcase breathing’ as a single phenomenon. A variety of breathing phenomena occur at different engine speeds, road speeds, and engine loads. 

To examine these phenomena the research findings are described under three riding headings i.e. with the bike stationary at idle (1000-1100rpm), under town riding conditions (1000-2500rpm), and at highway cruising (2500-4000rpm).  To begin, it’s worth noting there are two phases to at start-up.

    In phase one, there is no blow-by flow in the breathers for <30 seconds. This is due to wet-sumping and the Evo crankcase design, where piston down-force is used to evacuate the sump. Blow-by is held in the sump till the passage to the timing case is cleared of oil.

    In phase two there is relatively high blow-by flow (10-20L/m) for <10-30 seconds. This is seen on all engines with the Bunn Breather. It occurs as the crankcase air volume and hence pressure is reduced by the Bunn Inlet and Exhaust valves.  

1/ Engine at Idle (1000-1050rpm) –“Synchronous Breathing”-  Blow-by flow is highest at idle being 5-7L/m, (calculated as outflow minus inflow). Other writers point to this being due to e.g. longer dwell time. In this research, the neglected oil scavenge pump is a more likely cause. Recent research at http://www.hotbikeweb.com/tech/0212hb_high_flow_oil_pump/index.html

shows the trochoidal Harley oil pump loses pumping efficacy at low rpm. Below 1000rpm it fails to pump, (a warning to riders setting idle below factory setting). The oil pump scavenges up to 1L/m from the crankcase to the oil tank, but at idle, the breather has to take up this load. The inverse relation between blow-by and scavenge pump, is pivotal in this research. This pump has an important but unsung role in dry sump engine breathing.

NB:- Wet sump engines e.g. Moto-Guzzi require more breather capacity, as there is no scavenge side.

  At idle the pressures in the timing case are maintained at ambient pressure (760mmHg at sea level) and rockerboxes a little less (750mmHg). In the abscence of an engine timing hole, no sump readings were taken. (In the 1340cc Evo engine such readings show 750mmHg pressure, and less with a Bunn Kit.) In the 883 and 1200cc forms of the Evo engine, the gallery linking sump and timing case, plus five unsealed bushes in the common wall, allow free air flow. The Bunn valves visibly cycle together, metering in 1-2L/m into the timing case and passing 6-9L/m out the rockerboxes, via the Exhaust valve. They are operated by the piston pumping action in all single, parallel twin, V2 and boxer engines, and some multi-cylinder engines.  Blow-by is purged from the engine, while over-pressure is prevented.

Blow-by flow reduces to 3-4L/m.  The timing case pressure varies between 750-740mmHg. Rocker pressure ranges down from 750-720mmHg. (The gradient is partly due to the measurement of air at atmospheric pressure flowing into the low pressure timing case.)  Transparent Bunn valves uniquely allow valve function to be watched while test-riding. As rpm increases in this range, the valves start “skipping engine beats”. The Inlet valve starts to hold open, while the Exhaust valve maintains its beating. By comparing pressure changes, valve open/close states and the pressure gradient across the valves, it was seen that as timing case pressure fell, the Inlet valve tended to remain open between beats.  Similar tests (including blocking) of the Exhaust valve showed it remained cycling as rocker pressure fell. Clearly though anemometer readings cannot be taken while riding (for obvious reasons), the passage of blow-by via the Exhaust valve appeared to fall.

Partly this is expected, given the U-shaped curve of blow-by when compared to rpm. Also it reflects scavenge pump activity increasing. Lastly it suggests a polytropic process occurring in the crankcase. This involves alternate expansion and compression of crankcase air, with temperature and heat changes from blow-by gas entering the case. Given the present state of the art, it’s not possible to rank these effects.

The nature of the breathing here reminds of “demand breathing” with a diving regulator. The engine operates the Bunn valves at need, with more or less frequency depending on blow-by generation and ambient pressure conditions inside the engine, as well as conditions in the air the bike is rides through. It’s worth noting the chaotic combustion conditions when an engine fires at these revs. Rototest data show a 24% variation in the pressure of succeeding combustion strokes at their site http://www.rri.se/index.php?DN=30  This causes varying crankcase breathing, hence the aptness of the term ‘demand breathing’.

 Interestingly these changes in valve function are not seen during workshop testing with the bike stationary. There the valve function and pressures remain largely unchanged as rpm increases. This points to engine load and air-stream factors impinging on engine breathing behaviour.  We’ll look at this below.

The timing case pressure varies between 740-730mmHg. Rocker pressure ranges down to 720-700. Valve and gauge reading become more hazardous on road trials. At 4000+rpm a Sportster is travelling well over the speed limit. By carefully siting vacuum gauges, it’s possible to monitor valve function by gauge deflection. Atmospheric pressures were noted so the pressure gradient across the valves could be factored in.

As engine revs rise to 4000rpm, ‘road draft’ tube effects are seen. Without the tube, pressures fall slightly to 740-730mmHg. With the draft tube, pressures fall to 720-700mmHg. Gauge deflection and breather blocking tests prove Exhaust valve action.  Valve function is slightly depressed, as the rising vacuum in the rockerbox and falling flow, increases the pressure gradient across the exhaust valve. Polytropic effects are doubtless occurring. Still the inlet and exhaust valves cycle in response to engine rpm. Its likely oil scavenge effects are less potent here, as wet-sumping can correlate with rising rpm on Evo engines.  

Turning to the Inlet side, gauge pressures also declined and gauge deflection showed the inlet valve was still cycling, albeit within a tight range. There was no evidence of valve closure. Indeed, readings and observation of valve seal, indicate the Inlet valve tended to hold open, as road speed and engine speed increased. There is continuing inflow through the timing case by 4000rpm. This is striking evidence of the Bunn Breather crankcase-pumping technology in action.

As engine speed increases, the way the engine breathes changes. The Bunn Breather manages the engine alone at idle and low speeds. As speeds increase, the oil scavenge pump shares the work. At high speeds the scavenge pump effect may decline, leaving the Bunn Kit operating, till speeds go down again. Due to speed laws, no trials were taken at WOT.

This is not the full picture. The reality is more complex. With the same engines under load e.g. climbing a hill; these breathing changes occur sooner, and at lower revs. These changes are also seen on straight, level road as engine speeds lift.

They are not seen in the shop when the bike is run on the stand. Clearly there are other factors at work on the road and under load. It must be said the engines used in the testing were sound, well-maintained, low-mileage engines. A worn engine will develop more blow-by; calling more on the Bunn Breather. It’s worth noting the peak flow of my 2009 Exhaust valves is 36L/m. This provides a safe operating margin even for worn engines.

1.0 This research shows the patented piston-pumping action of the Bunn

       Breather, in road operation.

2.0 Different breathing processes occur under different conditions.

3.0 Road trials are necessary to plumb key crankcase breathing issues.

      Static and dyno trials are not enough.

4.0 The neglected role of the oil scavenge pump in breathing is reviewed.

5.0 The synergistic relations between Bunn Breather and oil scavenge

       pump are explored.

6.0 Forgotten aerodynamic factors have beneficial breathing effects with

      the draft tube.

Prior to 1963, nearly every motor vehicle on the planet used “Open Breathing” to vent its crankcase. Some 46 years later, this is largely forgotten. What could be simpler than plumbing in a short length of tube, into your crankcase? On motorcycles, whether classic, vintage or modern…the consequences of doing this, can be unexpected and unwelcome.

Proponents of open breathing on marque web sites expound the virtues of bigger and better open breather tubes. This perhaps culminates in the grotesque “elephants trunk” type of furled breather, used while disliked by Vincent owners. It seems a crude version of the idea... bigger must be better. It appears to have more effect as a standpipe than a breather.

Open breathers allow the engine to  s-u-c-k air in and blow air out, on succeeding piston strokes. A moments thought shows this allows the engine to s-u-c-k in road dirt, rain, dust, stones and insects etc; on every second stroke…not something  the typical rider would support. If you do this, a 5-10 micron breather air filter is absolutely needed, unless you’re prepared to accept accelerated engine wear and reduced TBO (time between overhauls). This is why such a quality filter is included in every Bunn Kit.

There’s the question of power loss as well.  Asking the piston(s) to

 pump air in and out the crankcase, as well as operating the

combustion chamber…costs the engine unproductive work and lost horsepower at the rear wheel. 

The question of horsepower is actually more serious than this: with open breathing. Recent research (my own and others), indicates the power gain available from optimising crankcase breathing, partly depends on creating a vacuum in the crankcase. The plain and unwelcome fact is… it’s impossible to create a vacuum in the crankcase, IF you opt for open breathing. In other words, if you install open breathing…you will cost your engine power. For many classic riders, this seems immaterial, but if you’ve only got 25-30 horsepower to begin with, losing even one is annoying.

The reason for the inability to produce a vacuum with open breathers, is touched on in Blog article 56/ below. As the oil scavenge pump evacuates the crankcase, air pressure falls towards zero (i.e. to atmospheric pressure). If the case pressure falls below zero, the scavenge pump s-u-c-k-s in air through the open breather. Thus the case pressure can never fall below zero: no vacuum is possible with open breathing.

This is sufficient reason to dismiss open breathing on any motorcycle.

NB: The correct term,  is disallowed by Bigpond for some reason, hence the use of the form... s-u-c-k, instead.

      On motorcycle web forums where crankcase breathing is discussed, (and given problems with breathing…that’s most forums), I can’t think of one where the role of the scavenge pump is fully recognised. Even forum old hands seem ignorant of its role. Why is this? 

The answer seems to be an assumption oil pumps should... well… pump oil. Many riders also assume their oil scavenge pump is submerged during normal running, even on a dry-sump engine. Both assumptions are incorrect. Even the froth and bubble in the oil tank after a run, doesn’t lead many riders to ponder it.  

A simple experiment helps. Strap a half-full, half litre (quart) bottle of cooking oil (EV olive oil is fine) to your fuel tank. Note the tidal ebb and flow as you accelerate, bank and brake. It’s clear the oil scavenge pump intake gets exposed and must often suck air.  A related point is oil with a lot of entrapped air, takes up more space. Engine designers allow for this expansion, but if our oil level is overfull (cf. Harley-Davidsons, Norton, and Royal Enfields), the frothing can force oil out the breather pipe onto the road. This is a common cause of breathing problems. 

Fact is on all classic and modern bikes, where there’s a dry-sump engine and the usual two oil pumps: the scavenge pump is designed to pump air as well as oil. It does so well, and in so doing, helps breathe the engine.    How much air can it pump, is a question on which classic (and modern) bike manuals are quiet. Recent experiments on e.g. the Harley-Davidson trochoidal oil pump, suggests it pumps up to about one litre (quart) per minute of oil (1L/m). In everyday riding, 0.5-1 L/m is nearer the mark. The scavenge pump may pass twice this amount of oil and/or air; or even more under some conditions.  

As usual with motorcycle engineering, there’s little published on this aspect of breathing.  Perhaps only Graham Bell notes the importance of the scavenge pump in crankcase breathing. (Four Stroke PerformanceTuning 2006, p292.)  Scavenge pump breathing is more important for crankcase breathing on some engine designs than others.  Harley-Davidson and Royal Enfield come to mind, BSA also.

There are three main research problems with motorcycle crankcase breathing.  

1/  There’s been very little research published on crankcase breathing in the motorcycle industry over the past 100 years. What was done was usually by designers and tuners and was rarely written down, let alone published. 

2/  Different crankcase breathing mechanisms operate at different rpm. At idle the Bunn valves operate in sync at engine revs. In low-cruising range the system moves to what I term "demand breathing". At high-cruising speed and above, the system appears to move into a "continuous flow" mode, whilst increasing engine vacuum even as it does so.  It’s ultimately impossible to uncover the mix of breathing processes going on in an engine, as rpm changes. What we can do is measure actual engine performance, apply as many gauges and sensors as possible, and do our best to interpret the evidence.  

3/  Workshop testing is of limited value. While engine breathing varies with rpm, it also varies with engine load. It varies with bike speed. Thus what is required is a ‘mobile dyno + instrument pack’, strapped to the bike for road testing.   Alternatively,  telemetry could be used with a range of pressure, flow and temperature sensors inserted in key areas inside every engine compartment, and around the bike frame.  Data could be transmitted to a roadside laptop.  This approach needs a MotoGP factory team budget to fund. I know what measurements need to be taken, and would be happy to collaborate with other researchers, tuners, teams or factories.  

Instead I take an empirical approach, testing every aspect of crankcase breathing, and accumulate books of data. Now I do more testing on the road, than in the workshop. Down the years, this archive allows  conclusions to be drawn via meta-analysis. If I can’t measure it, I don’t believe it.  Frequently, as in other engine tuning, counter-intuitive findings are seen that overturn engineering theory.  

Here’s an example of problem 3/ above,  using a Harley engine with a Bunn Breather.  In the workshop the engine returns pressure values of 750-760mmHg over the mid-rev range [ 0-1% vacuum]. The same engine achieves 6-7% vacuum under load on the road, at  the same revs i.e.  3000-4000rpm. What is happening?  

Two main reasons appear.

First, an engine under load from acceleration, climbing a hill or a dyno... may pass more blow-by due greater combustion pressures (holding speed constant). Thus it should have reduced crankcase vacuum.  In fact vacuum increases 5-6 times under load with a Bunn.

There seem two  possible reasons.

(a) The Bunn Kit (plus scavenge pump) is evacuating the sump faster than the engine’s increasing blow-by gas or,

 (b) The engine is passing less blow-by from better ring-seal, due the action of the Bunn Kit increasing case vacuum; (or there is a subtle third cause or causes to be discovered).  

Either way, the engine generates more power… if only because less combustion gas is escaping past the piston on the combustion stroke. I wish we had a portable dyno!  If we use Occam’s Razor, (b) above seems more likely.  

The second reason has less to do with the engine and more to do with aerodynamics. These data are from trials of a device to be standard on Bunn Kits. This device was originally designed to overcome the Altitude Effect discussed elsewhere on this Blog. The road testing shows benefits at all altitudes, and it’s being introduced in all Bunn Kits from April 2009.

Once we factor in aerodynamic aspects of the bike on the road, as they impact on crankcase breathing, it’s obvious there’s a limit to measurements taken in the workshop, or on the dyno. This is another contributing factor to the dyno results last year in the US.  

  One of the cardinal rules in motorcycle crankcase breather design is to avoid P-Traps (a U-Bend in USA). A trap forms when a breather line sags, or is bent down and then up, e.g. as your route it around the frame under the battery. If a breather line is lower in the middle than at either end, blow-by condensate will naturally form a lake in the lowest section of the line. As the fluid level rises, it blocks the tube and forms a P-Trap. 

 Every house contains multiple P-Traps in its plumbing system. Their purpose is to stop the passage of smelly drainage gases into the house. Of course in crankcase breathing, the passage of vapours is exactly what we want to achieve. Breather lines must be laid out to avoid such P-Traps.

P-traps don’t only occur in flexible rubber breather lines. They can be created by the engine designer and by designers of aftermarket breathers. Often we ride bikes with P-Traps staring us in the face, and don’t recognise them. Perhaps the classic example is the ubiquitous Horseshoe breather, sold by MoCo and aftermarket suppliers.

 

If you have one of these on any Evolution engine with factory head breathing, (or on any V2 engine), I suggest taking a long hard look at it, before removing it. You’ll find its design forms a nice example of a P-Trap…exactly where you don’t want one.

First let’s check the breather diagram,  say in an Evolution shop manual. We can trace the blow-by vapour path up from the rockerbox into the umbrella valve assembly. The vapour then passes down approx 40mm through a gallery to reach the hollow breather bolt. Vapour then travels sideways along the hollow banjo bolt into the banjo housing. After negotiating the tortuous path through the banjo, (losing pressure and cooling); it changes direction again to rise into the 6mm ID horseshoe breather tube. This 40mm riser section is what forms the P-Trap.

The volume of fluid that can collect in the horseshoe breather is as much as 20-30ccs. This is sufficient to block the passage of blow-by vapour in a 6mm ID horseshoe. If you’re thinking the force of the blow-by should somehow blow the tube clear…think again. The velocity at which blow-by travels is surprisingly low.   Also if a blockage occurs, the blow-by finds the path of least resistance, and this is via the rear cylinder. The result is the forward rockerbox holds still, stale air and moisture can build up, risking corrosion to valve springs. Only blow-by penetrating up the valve guides will disturb this stale air, forcing vapour back down into the timing case, and up the rear cylinder. Of course the formation of such a blockage depends on several factors inc. blow-by volume, temperature, engine use, crankcase pressure, viscosity of blow-by fluid etc.

The P-Trap only forms on the front cylinder, not the rear on the Evo engine; as the rear of the horseshoe exits blow-by downward.  However, if the rider curls the exit breather tube up higher than the end of the 6mm chrome breather tube… a second P-Trap is created on the rear cylinder. Blocking both front and rear cylinder breathers has serious consequences for any engine. Pressure buildup is swift and severe oil leaks are the first sign of this event.

 The Evo engine seems to cope with the forward breather blocked, so long as the rear breather is clear. In pressure testing the rear cylinder breather handles the extra volume of blow-by, at least on the test-bench. I’m not so sure with an engine at WOT or under load while riding. In any case why impede your engine performance by installing a component that seems designed to malfunction?

If you own a horseshoe breather on an Evo engine or any other V2 engine, I recommend removing it and checking for fluid or emulsion build-up on the forward cylinder. If you find any residue, I’d discard the horseshoe and install a breather design with no P-Trap.

The simplest way of doing this is to drop a breather tube from each head, and use a Y-connector (not a T-connector), inside or beneath the aircleaner housing. This is the approach taken with Bunn Breathers and it prevents P-Traps forming.

One of my 2009 R&D projects focuses on how movement of blow-by gases in and out the engine, affects engine performance and power.

This was prompted by last years dyno work in the USA and by another Australian classic motorcycle researcher Graham Bell (Four Stroke Performance Tuning, Haynes 2006, pp292-294). While spending ( like all top bike authors)...little time in his books on breathing Bell noted crankcase pressures aren’t uniform. There are areas of high and low pressure, depending on the movement of engine components, and resulting aerodynamic effects. Bell noted e.g. that fast-moving shafts create a low pressure area around them.

This explains e.g. why oil sticks to flywheels and causes drag and power losses. There are low pressure areas surrounding the flywheel and higher pressures elsewhere around the crankcase. The lower pressure air around the flywheel means gravity cannot overcome it and drop the oil into the sump… hence I suppose the fitting of scrapers on classic British flywheels.

Bell saw this as a key reason for power increases associated with crankcase breathing on dry sump engines. Dropping crankcase air pressure towards zero, or even below zero  (as the Bunn Breather does), overcomes the pressure differential inside the crankcase, and  reduces the volume of oil sticking to fast-moving shafts etc. This cuts oil drag and naturally a power increase follows. That squares with my research also.

The second effect leading to reduced power losses is that covered in my book and previously noted by Falco. This stems from cutting wasted work by the pistons, in pumping air round the crankcase.  In brief, if you can reduce the circulating air volume in the crankcase, the pistons can more easily pump it around. Further if you can manage the air in the crankcase so there’s less air on piston downstrokes and more on upstrokes…you can further cut wasted piston work. That’s precisely what my breather technology is designed to achieve. In the next article I’ll go further into how to harness these effects on your own bike.

Update:- Please go to article 82/ for the latest road-test evidence of power increase with the Bunn kit.