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The March 2011 edition of Motorcycle Consumer News USA, published a lengthy article of mine on crankcase breathing. This report fully relates my latest research into the subject. It aroused a great deal of discussion in the USA but has not been accessible to riders outside the USA.

 With the editor's permission, I reprint the three page article here for the benefit of international riders. 

Your Donations Accepted-

5000 riders visit this Bunn web resource every month, and the number keeps rising. This is gratifying. My research over the years helps riders around the world. Most riders find assistance and solutions to their problems here and don't go on to purchase a 'Bunn Breather' kit. This is the way it should be.

I am now retired and plan to continue research into crankcase breathing to benefit classic, vintage and contemporay riders.

It's suggested I publish this Blog as another book and so profit by it. Instead I'll continue to publish research into the public domain, and support classic motorcycling everywhere.

To encourage this I'm now accepting your donation to assist in running the research projects.

Your Action;- if you find useful info and solutions here, you may want to join the research and contribute a small donation to the research program. Simply make a Paypal remittance to me at this address

rexbunn@bigpond.com on www.paypal.com.au

I'll acknowledge your donations in an Honour Roll to be erected on this Blog.
Thanks and best Regards, Rex Bunn  

I've not sofar shown a "Warm Air Induction' example so today photo'd the unique army TR6R restoration when it got to the stage of receiving it's breather. I opted for a Bottom>>Bottom installation on this bike,as the bizarre factory breather via the chaincase, means the driveside oil seal is missing. Riders often block the three small holes in the crankcase wall, thinking they're blocking the breather but they're not. The holes simply form an oil weir in the crankcase, while the engine continues to breathe through the shaft bearing, as do many bikes. Thus if you want to disable the Umberslade chaincase plenum chamber approach, you need to first reinstall the mainshaft oil seal.

I installed the Bunn Inlet assembly along the top engine steady, terminating against a handy nut, and punching transverse holes through the inlet tube, to allow plenty of air ingress from the (relatively) still, warm region above the rockerbox. This connects down past the inlet manifold and into the timing drilling. The tube describes a number "3" shape in warm air and the Inlet valve is horizontal-to-forward sloping, helping to leave the valve in a "normally closed' position. This is handy to minimise valve fouling, as the hot engine passes blow-by vapour up breather tubes for some time after switch-off. in fact recently I started routinely including a baffle in the Inlet assemblies to intercept this before it reaches the air filter. This pushes out air filter service life.

The Bunn Exhaust line exits the OEM chaincase breather, using a rising section to stop oil fling (although the chaincase has a nice baffle already), and passing down behind the frame to terminate in a Draft Tube clear of the rear tire. The oil tank breather tube joins this in it's end stage and the two are tied for mutual support. A further detail. If you zoom onto the carby, you'll see self-amalgamating tape sealing the control cables, a common cause of carby and fuel contamination in wet and dusty climates.

 A crankcase breather tube copes with a damaging internal cocktail of materials in blow-by vapour, plus damaging external stressors. These reduce the service life of any tube. Ideally a breather tube material will handle exposure to mineral and synthetic oils, petroleum and alcohol fuels and combinations and emulsions of these: but that is only the beginning. The tubing must also face combustion products i.e. water, steam, acids and heat, without swelling or water absorption. It has to be impermeable to blow-by gas. It must also be tear and abrasion resistant.

Externally the tube has to withstand oxidation, ozone, sun damage and extreme winter cold in e.g. Finland. It must have good elastomeric properties and hold its profile as it winds round the bike frame. It must also look good on classic, vintage and concours bikes. This is why I changed from high-grade clear PVC to black rubber years ago, though  rubber in some respects is inferior to PVC in this application. However a breather must look authentic on a classic bike.

One problem with rubber is it’s a natural product and varies from batch to batch, recipe to recipe and compounder to compounder. There are no specifications per se for rubber, as we find in other branches of engineering.

Passing blowby vapour is a challenge for any rubber tube. Oil fractions in the vapour attack most rubbers. Of the leading seven types of rubber only neoprene and nitrile suit this task, and neoprene barely so. Fuels attack most rubbers, save these two and nitrile is better than neoprene on both counts.

Looking outside, neoprene handles oxidation, ozone and sunlight better than nitrile. Perhaps an ideal blow-by breather tube would combine nitrile inside and neoprene outside. However the cost of such tubing pushes kit prices above the range acceptable to most riders.

The solution I currently use is a high quality nitrile-rich tubing recipe for automotive use, made by a local compounder I know and trust. This handles blow-by vapour and crankcase gas better than other rubber compounds we immersion tested. Still, it’s only as good as the PVC grade we used previously. Even with this grade we occasionally  have reports of deterioration and these seem due to sun and ozone cracking, and in arctic regions extreme Winter cold. I occasionally see surface cracking after a few years service, but only in exposed areas prone to vibration, and where the rubber is stretched over a union.

When choosing tubing, it’s wise to look behind the label. Compounders typically  combine cheaper and more costly rubber grades in their extrusions, often under the same generic name. Beware of mutton dressed as lamb. After facing a global product recall years ago because of  a deficient rubber grade, I suggest riders ask for a material specification when choosing rubber products for motorcycling applications. Oh, and it'll help your breather tube last if you can keep it out of the sun...not always easy on a bike!  

Father Time tells me it's time I considered retiring, again. As a result I invite interested parties to contact me to discuss purchasing the Bunn Breather business. The business would suit e.g. any motorcycle rider with a bit of curiosity and/or a technical interest in motorcycling. You don't need to be a mechanic or engineer. I've been successful precisely because mechanics and engineers failed to investigate this branch of motorcycle engineering, since pioneering days.

Riders looking for a way of combining their favourite hobby with an income, may find it attractive. How else can you legally write off your motorcycle and riding expenses as tax deductions, with Tax Office approval!

It's ideal for a retiree looking to extend their involvement in motorycling, or to assist other riders enjoy their sport. It suits riders with a classic or vintage interest, or an interest in performance  and racing. Only a small workplace is required.

The business sale will include the patents, production equipment, stock, intellectual property, Bunn domain and website, Kit designs, know-how, marketing material,technical files, research files, User Guides,client database,international distribution network,introductions to suppliers and training during the hand-over period, so you get up to speed rapidly.

Interested riders can contact me by email at rexbunn@bigpond.com

Hi, The Blog editting software is on the blink again. For the Index to reports please scroll down past reports 112-109 and you'll find the Blog Index there. Apologies for this. Telstra are once again investigating reasons for this.  

This 1973 Moto Guzzi Eldorado owner employed a three valve system we devised to suit this engine. Breathing Bottom>>Up and using the OEM crankcase breather union, the owner has achieved an outstanding result, commenting...

“I now have it with the tubes just venting to atmosphere below the engine, in the airflow. The system works perfectly , as it should, moving air through the engine. I noticed a power improvement in the bike right away. Using the stock Guzzi breather "box" I would get oil puking out the vent hose during a sustained high speed run, now with the Bunn breather, that no longer happens, even if I run the bike up to 95 mph + for sustained periods.”

 A lot of crankcase ventilation fundamentals are undocumented. This is not to suggest research hasn't been done; rather that it's unpublished and/or held as trade secrets by tuners, race teams and marque competition departments. Thus many of these Blog reports contain the first published research on the topic. This is another one.

This question prompted me to review recent records on bikes tested, based on the old engineers axiom..."an ounce of data beats a ton of opinion". Like most riders I assumed a correlation between engine capacity and blow-by volume. It was surprising to find the situation unclear. In the first chart below, the trend line appears to show an association but it is weak. The scatter diagram shows no meaningful connection.

NB: No chart showing yet. Sorry.

I next split the bikes into low mileage and high mileage bikes with worn engines, in the second chart below.

NB: Chart not showing for some reason. Again sorry.

There is a bit more association between engine capacity and blow-by volume in high mileage bikes, but it's still small and more at idle. At cruise rpm the association declines. Perhaps up to a third of blow-by might be explained by engine size. A larger sample is needed to be sure. How significant are these findings?

In this small sample (n=17), there'll be measurement errors and the bikes tested weren't randomly selected. Also the test results were partial, taken with stationary engines. They were all taken with the same flow meters.

These data show little support for the assumption bigger engines need more breathing i.e. that say a Harley-Davidson TC96 needs more breathing than an 883XL. In practice a 650cc British twin puts out as much as a Harley.

There is a weak link between engine size and blow-by volumes in worn engines. Beside wear, this might reflect the increased space around the larger worn piston rings, through which more blow-by escapes. Piston ring length rises at half the rate of piston area, as engine size rises. There's relatively less gap as engine capacity increases. That is perhaps one cause. There are others and research is needed.

 Mean blow-by volumes were 7.4L/m at idle and 6.3L/m at cruise. Range is 3-14L/m idle and 2-12L/m cruise. On a related note, race car tuners use a rule of thumb for blow-by in large engines as below:-

Car engine max HP/50 = blow-by in cfm

 Ex:- a V8 developing 500hp

 500/50 = 10cfm or 283L/m of blow-by

Taking this rule back to say a 50hp Sportster gives us 28L/m. This is way over anything measured and shows car rules don't apply to bike engines.

 We can't address crankcase breathing without first understanding the lubrication system of any bike; for the two work in conjunction. Crankcase breathing can be considered an extension of the lube system.

With the popularity of Bottom>>Up breathing due to ethanol fuels, the question arises of how to breathe out a rockerbox without interfering with oil return from the same box.  This is explored in Blog report 97/ with reference to Triumph and Harley-Davidson engines. Maida and Zimmerman (2005) reported such an issue with the Harley Twin Cam 88 engine, where oil return was impaired by oscillating pressure in the oil return drain. Oil built up in the rockerboxes and eventually overflowed into the head breather. Some years ago I estimated the pressure required to "hold up" the return oil down a Harley-Davidson Evolution 883cc engine as just 13.4mmHg. This represents <2% over atmospheric pressure, a condition often seen in engines with even slight wear and recycling OEM breathing.

This week I ran in vitro experiments to confirm that 13.4mmHg estimate and explore what happens to oil return from rockerboxes. The findings were surprising, viz:-

 1/ With a test-rig loosely based on the Evo quad-cam oil return dims i.e. a 25cms long drain of 5/16" ID... a pressure of 10-12.5mmHg was indeed sufficient to prevent SAE20-50 oil descending the pipe. This agreed with the theoretical estimate years ago.

This engine like many OHV and OHC engines, has other airways connecting rockerbox with bottom end, so the finding does not mean there is always a problem. Still, a pressure differential across any oil return pipe is unhelpful for efficient oil return. For those engines like Harley-Davidson, that breathe out their rockerboxes AND have a tendency to blow oil out their head breathers as mileage goes up... such a differential could be a factor in poor crankcase breathing. To explore this needed a second rig.

 2/ With an 8mm and 12mm twin-pipe test rig (based on Evo oil drain and pushrod tube area dims), the results were striking. With a 10-15mmHg pressure differential across the rig, and air pulses introduced at the bottom with oil introduced at the top...air preferentially passed freely up the wider tube (read pushrods) while simultaneously oil passed freely down the smaller tube (read oil drain). This trial was repeated several times with the same outcome. 

 I expected the lesser weight of oil in the smaller drain column may have yielded to the air pressure, before the heavier oil column in the pushrod column, yet this is not the case. To gather more data on possible viscosity factors, we repeated the test with water replacing oil and saw a similar, less marked result..

We conclude there is a clear preference for the larger pipe in both water and oil tests. These findings imply for motorcycle crankcase breathing:-

 1/ 2/ A blow-test should be done routinely in all bikes, to check for patent airways.

2/ In deciding on a Bottom>>Up breathing pathway there must be at least two, dissimilar sized airways between top and bottom engine compartments. This is the case for most classic contemporary OHV and OHC engines. Engines with tappet blocks obstructing the pushrod tubes frequently prove to be drilled, providing a second airway/oilway while lubricating the tappets.

 3/ If only one airway/oilway exists, then Bottom>>Up breathing is problematic. Top>>Down breathing is still of course possible, as return oilways normally carry oil with entrained air.

4/  In commonly sized oil return ways of 1/4- 5/16", even a slight pressure differential (<2%) may impede oil return, irrespective of breather design.

 NB:- This is a potent argument in favour of maintaining mean crankcase/timing case pressure at and preferably below atmospheric pressure i.e. to enable and certainly not to impede oil return.

 5/ In Bottom>>Up breathing, with two or more dissimilar diameter air/oil ways, a kind of circular oil and air flow will develop i.e. oil will other things equal return to the sump via the smaller diameter pipe, while blow-by will naturally pass up the larger diameter pipe. These flows are driven by the differential forces acting in the pipes. Given force = pressure X cross-sectional area, the Bottom>>Up blow-by column finds it easier to make its way up the larger pipe(s), leaving the oil to descend the smaller pipe(s), in an elegant symmetry.

It seems likely those engine designers e.g. Harley-Davidson and Meriden Triumph who provided airways through pushrod and cam-chain tunnels, were aware of this phenomenon in designing their lubrication systems. In designing crankcase breathing solutions, it's important we work with these oil and air pathways in mind.

With all engines, these tests show the merit in reducing pressure pulsations in the crankcase and connected compartments, and in reducing crankcase pressure generally. My system is uniquely designed to do both these things. Even small pressure reductions appear to have favourable effects on the lubrication system. In high-mileage bikes and those with compromised oil pumps, optimising crankcase breathing may enable the rider to postpone a major overhaul.

All four-stroke engines develop blow-by vapours. While my research focuses on motorcycles, I also looked at cars, planes and boats. Recently I looked at lawnmowers, after refurbishing a couple of Briggs Stratton engined lawnmowers for family members. While a fan of Briggs Stratton (B&S) engines all my life, I didn't like what I found and so invented a breather kit to stop the engines fouling and to give them a second service life.

BS mower engines are small single cylinder four-stroke, wet-sump engines. They follow OEM motorcycle practice and use a recycling breather from the sump to the carby intake. They use an alloy tube for this connection, probably as a crude blow-by condenser and on some models, a small  expansion chamber adjacent to the carby, no doubt to encourage gas slowing and further condensation and deposition of oil mist, prior to it entering the carby. Some appear to further use a Harley-style flow restrictor between the surge chamber and carby, though this may also be to avoid disrupting carby air pressures.

On these engines for refurbishing, there was a lot of oil smoke from the exhausts and I was struck by how much soft, wet soot build-up there was in the combustion chambers, beyond that normally seen on motorcycles. The engines were otherwise in usable condition. I noted oil deposits in the breather tube and clearly it was being sucked and/or pumped into the carby and burned, thus helping to account for the pronounced carbon build-up.

A blow-test showed airflow between oil filler spout and breather, as expected on wet-sump engines. There was pronounced crankcase pumping, typical of single-cylinder engines.

I made up a breather kit as shown, adapting a superseded Bunn Blow-Bye Kit I had lying around the workshop. This comprises an exhaust valve assembly that redirects the blow-by to ground and a blanking cap  for the carby. The Kit operates nicely now and the engine seems to like the new breathing. The exhaust smoking has completely stopped now, proving inter alia the breather was contributing to oil burning. While only a single valve breather, it is dropping mean crankcase pressure and this is no doubt helping the engine run more happily.

In reflecting on these two engines and a third Sanli mower I breathed last year, I see as on trials and enduro motorcycle engines operating in dirty conditions: mower service life can be extended by improving breathing. As well, mower engines like bike engines operate while moving and are often tilted and banked as the mower follows ground contours, again much like motorcycles.

The operating conditions when coupled with a wet sump make oil fling up the barrel more pervasive than on bike engines and oil penetration of the combustion chamber extensive than on bikes or cars. This latter factor, coupled with a recycling breather, plus normal engine wear; account for the very coked up B&S combustion chambers. After scraping out the wet carbon the engine cleared a large amount of residual carbonised build-up and now starts first kick and seems to have a new lease of life. I wonder how many otherwise sound mower engines are needlessly replaced because of poor crankcase breathing?

Shown below is one of the Briggs  and Stratton engines with Bunn Blow-Bye Kit

A new website will operate during February 2011. www.bunn.co.nz will extend the work on this Blog and contain more user-friendly information on Bunn Breather Kits and crankcase breathing matters.

 The new site will contain links to this Blog and this Blog will continue as a unique resource for motorcyclists on crankcase breathimg issues and problem solving.

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.

INDEX-This index covers the 111 reports on this site to date. The reports are "stack-filed" and spread across 3 pages.

Reports 1-4 are on page 3.

Reports 5-55 are on page 2.

Latest reports 56-110 are near the top of the stack, on page 1 below.

NB:-The resource has reached 111 reports and photo galleries. It is migrating to a website. Meantime navigation is becoming an issue. Reports are subject colour-coded for easier selection, as below.

All Bikes- Reports for all riders

Brits- relevant to British marques

BSA- Marque installations reports

Cars- Of car breathing generally

Classics- Reports for classic riders

DIY- Breather Tips for any marque rider

Ducati- Marque Reports

Harley-Davidson- Marque Reports

Moto Guzzi- Marque Reports

Norton- Marque Reports

ROAD TEST- On-road breather testing

Royal-Enfield- Marque Reports

Suzuki- Marque Reports

Yamaha- Marque Reports

Triumph- Marque Reports

Velocette- Marque Reports

Vincent-Marque Reports

VW- Marque Reports

How To Use Index- First select a report number.

How To Navigate:- Hit the "Down Arrow" at the bottom-right corner of your browser. Arrow down through the reports and pages, till you reach the one you want. The reports and pages 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 Telstra Blog tools.

Customer Service

Breather Kit Sales Enquiries to rexbunn@bigpond.com

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

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

Harley-Davidson Sales Enquiries to rexbunn@bigpond.com

UK Triumph Breather Kit sales- Contact me at rexbunn@bigpond.com or email Paul Fotheringham at Shropshire Classic Motorcycles info@triumphbonneville.com or call 0044(0)1743860146

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

          Reports Index

111 Do Larger Engines Need More Breather Capacity? 

110 Crankcase Breathing and Rockerbox Oil Return 

109 Stationary Engines- Crankcase Breathing 

108 Harley-Davidson Why Does the Oiltank Overflow?

107 Royal Enfield-Breather Development History

106 Moto Guzzi -Blowby Layers in an 850T

105 All Bikes- Buy Your Bunn Breather Kit on EBay

104 Classics -Installing the NEW 2010 Bunn Classic Kit

103 Classics -New 2010 Bunn Classic Breather Kit Launches

102 Royal Enfield- A Very Special Custom

101 All Bikes- Does Venting Blow-by Alter Your Mixture?

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

97 All Bikes- Triumph- Ethanol Forces Bottom>>Up Breathing

96 The Ultimate Reference to Global Warming

95 Classics - DIY -Making Oil Feed Taps More Safe

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

90 Why Crankcase Breathing sounds like Smoke and Mirrors

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

83 BSA- Breathing the Last Gold Star

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

81 Brits/Harley-Davidson A Critique of Timed Breathers

80 Ducati -1976 Ducati 900SS Installation

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 Bikes- Ethanol Fuels and Crankcase Breathing

75 BSA-The Best A50 Research-Based Installation Sofar

74 Cars -Breathing Air-Cooled Race Car Engines

73 Triumph /BSA- Advisory for 750cc Triple Owners

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 Bikes- 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-Tube-DIY Guide added

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

57 All Bikes- Why Open Breathers S-U-C-K

56 All Bikes- Neglected Oil Pump Breathing

55 The 3 Top Problems in Crankcase Breathing RD

54 All Bikes- P-Trap Perils Horseshoe Breather Block

53 All Bikes- How Can Bunn Kits Increase Power?

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 Triumph-Causes of Bad Breathing/Wet Sumping

39 All Bikes- A Note on Nitro and Methanol

38 Yamaha- Breathing the Virago V2 1100cc engine

37 Harley-Davidson - 2004 Evo Sportster Installation

36 Harley-Davidson- A 1340cc Evo Installation

35 Velocette-Installation- A Creative Example

34 All Bikes- Thirteen Rules for Crankcase Tuning

33 Triumph - One of the Best Bunn Installations

32 Harley-Davidson - Testing Umbrella Valves

31 Triumph and BSA- DIY Handy Breather Tip

30 GALLERY: Norton Pristine Commando with 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 on a Yamaha 1100

19 GALLERY: Norton - Commando with Bunn

18 GALLERY: Triumph Pics with Bunn Breather

17 GALLERY: Royal Enfield- Curing Blow-By

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

15 All Bikes- Whats Coming Out of Your Breather?

14 Harley-Davidson- MkIII Breather for Evo Sportster

13 GALLERY: Harley-Davidson- 2008 Sportster Install

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 Donrsquo;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

All dry-sump motorcycle oiltanks must ultimately breathe to atmosphere. Otherwise the oiltank would quickly become pressurised by scavenged blow-by gas returned to the tank by the oil pump. Harley-Davidson have for years directed their oil tank breathers to the cam gear case, rather than to atmosphere. While this may help meet EPA requirements, it has deleterious effects on the engine. These can be remedied as part of an engine breathing solution.

As the Sportster oiltank pressurises and the oil filler cap has a seal this air pressure has go back to the cam gear case, further contaminating it with corrosive blow-by vapour. The vapour and pressure then has to vented a second time from the head breathers, along with the regular load of blow-by vapour passed into the cam gear case from the sump. This is poor design, back-loading the breather system with a second load of blow-by. (The reason engines breathe is to void waste products after all). As the mileage goes up and the engine wears, the breather system starts objecting to doing double-duty, by spitting out oil and blow-by condensate.

While all worn engines eventually do this, the Harley-Davidson design ensures they do it earlier. This is unhelpful for the rider and may force an expensive engine rebuild before it's due. While alternative engine breathing arrangements can resolve this, it's worth studying why and how such oil tanks overflow so easily.

Firstly, the engine design makes it hard to take a reading of the engine oil level. As a result many riders over-fill the oiltank and get overflow. Such overfilling is hidden from the rider as it passes invisibly back to the cam case. The first sign can be oil smoke from the exhaust.

Second the bike and oiltank design encourages overflow, rather than preventing it. How can this be? In principle the ways fluid can exit an oil tank breather are:-

a/ If the fluid level rises to the level of the stand-pipe inside the tank and overflows into it.

b/ Any mechanical damage, cracks etc to the standpipe itself,

c/ At high speed the oil return pipe sprays bubbling oil up to the roof of the shelf, and some drips down into the breather pipe.

NB: On the Sportster the distance between the two pipes is just 2.75"

d/ The fluid level is close to overflowing and the bike is tilted to the left (in cornering or putting it on the side-stand), causing the oil in the main tank to rush across into the left-side oiltank compartment, and slop over into the stand-pipe.

NB: if this happens with the OEM set-up there is no sign of it. If a Bunn kit is used, there is no sign of this for several minutes till oil passes down the new breather tube to atmosphere.

Similarly, once an overflow starts exiting the breather tube, it keeps running till the oil bolus has passed down the breather tube to atmosphere. The symptom persists after the cause is removed. This makes for difficult diagnosis by the roadside. One useful side benefit of a Bunn kit is in alerting the rider to an over-full oiltank.

If the plastic Harley oil tank was in one section overflow may not happen. However the designer formed the tank in two sections i.e. the main tank and an elevated lateral 'shelf-like' compartment jutting across to the left side. Presumably he/she was short of capacity and decided to use the waste space behind the battery. However he failed to consider the movements of oil across this shelf.

This shelf floor is 2" higher than the main tank floor and contains the breather standpipe and the oil return standpipe 2 .75"apart. The breather standpipe is in line with the left side of the rear tyre, i.e. left of the bike mid-line. If you remove your LHS battery cover and shine a torch behind the battery, you'll see the two pipes entering the shelf.

Part One- This report is complex as it describes the bizarre India Bullet breather design. It's a first draft and will be revised as more research comes to hand.

Motorcycle lubrication systems interact with crankcase ventilation. On the Royal Enfield engines, especially the later Indian forms it is impossible to evaluate crankcase breathing unless the lubrication system is considered.  The British Royal Enfield Bullet design harks back to the S, G and J engines of the 1930-1949 period. The design path can be traced to the final Indian version of the British bike, the 2008 500cc Classic and de Luxe models. A couple of caveats. First, my experience is with models from Royal Enfield Australia though I work with riders in all countries. Second, the 2004-2008 Electra model has different lubrication and crankcase breathing. This development history focuses on the post 2004 period. First the timeline.

Development Timeline 1937-1949- The 250-500cc S/G/J models established the design for later Bullets. The oiltank was in unit with the crankcase casting but separated from the sump into two compartments, forward and aft of the sump. The two compartments breathed to air via a forward filler cap drilling and a passage to the aft compartment head-space. In WWII models, these were blocked and the engine breathed into the timing case via fore and aft drillings. This engine would have mainly breathed via it's oil pump. Perhaps this lead the Indian plant to follow this path? 

 The oil pump was a plunger type, initially operating at 1/18 engine speed, with a low output. After WWII the meagre output was increased by upping pump speed to 1/12 engine speed. This would have followed the shift from roller to plain big-end bearings, and the need for higher oil feed pressure. The early engine breather system was formed by a 3/16" mainshaft drilling. There was initially no disc valve and the engine breathed openly into the chaincase. This was of oil-bath type and blow-by vented to air.

 1949-1951- 350 G2 and 500cc JS Bullet models. Mainshaft timed breather has a disc valve, vented via the chaincase to ground by a short tube.

1952-2003-A new Bullet breather via a left side crankcase union, with blow-by piped to the chain, later using a duckbill restrictor.(see report 92). The union was high up on the side, close to the flywheel rim. This is not an ideal union position for an open exhaust breather, given the low pressure zone. On the other hand it was sheltered from the oil feed and oil fling. Bikes toward the end of this period show varied breathers. Some mix barrel and oil tank unions. Others have oil tank unions only. Both latter types should have a crankcase-oiltank drilling. It appears the Indian factory was experimenting. Little was published in the way of technical information from the plant. It's surprising Snidal published the best workshop manual in Canada which had no Bullet imports. Egli and TPV were reportedly asked to advise on crankcase breathing. The plant apparently ignored their advice and went with AVL, an Austrian diesel/instrumentation consultancy. I presume this reflected the Eicher purchase of the plant, and previous links with AVL via the Tata division? What resulted was strange breather design.

2004- 500cc Bullets introduced in Australia by REA. Classic and de Luxe models with breathing via oiltank and timing case. 

 2006- 500cc Electra introduced with AVL engine, gear oil pump and roller big end. Breathing as for the Classic. We consult to REA to resolve Classic and de Luxe breathing problems.

 2007-We consult to REA to resolve breathing problems with the Electra (see report 84).

2009- New UCE engine introduced with trochoidal oil pump, wet sump and recycling breathing, from the case roof. Breather performance over time remains to be seen.

Lubrication There are three generations of pump i.e. the spindle-type double-acting oil pump, a gear pump and the new geroter pump.  As with other British manufacturers little information was published on pump flows. Changes in big-end bearings drove changes. I estimate the spindle cruise speed flows at 0.5L/m to WWII, increasing later to 0.75L/m. The later gear pump discharge would be approx. 1-2L/m. The new geroter pump flows more up to 3L/m. Scavenge pump flows ought to be 50-100% more. All figures depend on pump condition. As riders rarely check oil pumps actual flows are often less, in some cases barely measurable. (By comparison car oil pumps flow 30-40L/m.) The gear and geroter pumps pump blow-by gas; the spindle pumps also.   British design had the scavenge pick-up in the sump and carried via external lines to the rockers, whence it fell down the pushrod tunnels into the timing case. The British had only part of the return oil going to rockers...the Indians have all the return oil going there. The larger Indian volume of oil through the rockerbox quietens it but makes it hard to find a sheltered spot via which to breathe the engine. This limits breathing solutions to the bottom end, timing case and oil tank.

Other Indian oiling changes include removal of oil bypass valves, oil return galleries, relocation of the timing case oil lifting mechanism, (this niftily used the timing case pinion gears to lift return oil up to a drilling in the oiltank-case wall as in Indian Scout design. A variety of drillings were tried in the forward and right hand oil-tank walls. Breather unions were installed in the timing case, chaincase and oil tank roof.

2004-2008 Factory Crankcase Ventilation- The British efficiently vented blow-by from the sump via the left-side barrel union. They did not vent their timing case which contains blow-by scavenged from the sump. Blow-by and oil returned to the oil tank via a drilling in the oiltank wall. If/when the timing case flooded, a weir formed across the oiltank. Blow-by then vented to air via a hole in the filler spout cap. This is the crankcase ventilation system inherited by the India plant.

The India plant removed the British breather system. They sought EPA compliance on crankcase emissions enabling export sales. There was no EPA emission test for crankcase emissions only a ban on emissions. The test is a visual check, i.e. there are no open lines from the crankcase. India would have passed the visual test by connecting all engine compartments to a canister under the seat, joining this to the carb air intake...and called it a recycling breather. Whether this was an AVL solution or from in-house I do not know. It was not from TPV (personal correspondence).

 The visible details of this legerdemain are:-

a/ Barrel breather union blanked off.

b/ Oil tank cap breather blanked off.

c/ Timing case-oiltank wall return hole blanked off.

d/ A 10mm central drilling in the oiltank roof forming the main crankcase vent.

e/ A 6mm drilling in the forward oiltank-sump wall. This drilling is rarely discussed. The drilling lies on a line between the 10mm top union and the top nut below and right of the engine number. This drilling angles up at a 25-35 degrees from the oiltank headspace, and enters the crankcase adjacent to the left side of flywheel.

 NB:-This is an important drilling with a role unsuspected by owners, agony aunts or factory.

f/ Two new drillings were made in the timing case-oiltank wall. These are below the British drilling and on the opposite (i.e. lower) side of the pinion gear array. On this side of the timing case the pinions are opening not meshing, so little pumping or oil-lift action occurs. The Indian designer seems to have been aware of this and removed the British gear shrouding. The new lower drilling replaced the original British oil return hole while lowering the resting fluid level and volume in the oil tank. The new drilling above it is supposed to let scavenged blow-by gas enter the oil tank headspace, whence it can exit the oiltank roof vent.

In practice, when the timing case floods, the fluid level in the timing case can rise to cover both the new drillings. In some bikes, the oil continues rising, and may enter the so-called drain line, from the catch-can. When this happens the timing case headspace pressurises. This can force timing case oil up to the catch-can and out over the silencer, the so-called elephant snot.

g/ An 8mm union is inserted in the inner timing case inner wall, above the oiltank roof. This top union is supposed to drain blow-by fluid back into the timing case from the catch-can. Part of the time it cannot given conditions in f/ above.

h/ When the timing case floods, scavenged blow-by vapour is blocked from entering the oil tank and forced to pass up this line to the catch can. Chaos results in the timing case and oil tank, giving rise to what I term the "cappuccino effect" which forces oil-froth up the oiltank breather.

i/ A 6mm union is inserted into the primary chaincase ceiling on the Electra.

j/ The three new unions are connected by hoses to a small metal catch-can up high under the seat. The catch-can is connected to the airbox by a short hose.

k/ A duckbill valve lies inside the can on the 10mm line. Another duckbill is found inside the 8mm timing case union.

l/ Another duckbill was retro-fitted to the timing case-catch-can line ca. 2007. The latter followed the Indian plant studying the Bunn Breather Kit, after purchasing two. This duckbill is potentially patent infringing, appearing to imitate a key Bunn design. Given the confusing dozen plus Indian design changes, it's worth summarizing the functional effects below.

The claimed breather function is that blow-by passes into the oiltank and up to the catch-can from the oiltank union. The vapour is sucked into the airbox, in a pukka recycling system. The condensate (elephant snot to Enfield riders) is supposed to run back into the timing case via the new 8mm hose and union in g/ above. In practice (as the British oil-lift gears are inoperative and all oil return is pumped to the rockerboxes, whereupon it drops down the pushrods to the timing case), the timing case fills up with oil and becomes a second oil tank. (This is germane to later discussion.)

As well, the designers failed to consider the oil pump is trying to return blow-by to the oiltank via the timing case, even as crankcase blow-by is trying to expand the other way, i.e. into the timing case head-space. This helps explain the extreme frothing in the oiltank at high rpm. This hyper-frothing has to be reduced if the engine is to be breathed, see below...

The three drillings in f/ and g/ above all become submerged as the increased scavenge pump return floods the timing case. As bikes wear, the mainshaft oil seal can leak and the oil feed pump can leak oil into the timing case instead of the big end, accentuating oil build-up in the timing case. Oil mounts the 8mm timing case line at higher rpm in the Electra because of this. The Classic and de Luxe are less prone. With some clients the quantity of oil and blow-by is so great it passes into the airbox and floods over the silencer. In some conditions, oil passes into the chaincase and fills it, or empties the oiltank onto the road. Clearly all is not right with the breather design.

Bunn Breather Kit design- We elected to work within the constraints of the existing unions. There are so many breather drillings and unions I couldn't bring myself to build more. With the Classic and Electra we breathed in via the timing case union and out the oiltank union. This helped the Indian timing case line function as designed. To solve P-trap problems with the factory breather we lead the exhaust line up for 100mm. This also replaced the absent froth-tower. Part of the Bullet problem is inadequate headspace in the oiltank which was never designed to breathe out its roof. A froth-tower is mandatory in this situation.I expected baffles would assist by cutting turbulence.I road-tested an Electra up to 120kmh with this set-up and it worked. To be sure we co-opted UK and Oz Electra riders into a public pre-launch trial. We passed that trial and introduced the Electra Kit.

All went well in 2007 and 2008. Late in 2008 I heard of isolated problems with Electras. Oil was getting past the baffles and venting, especially as mileage and wear increased and hot-up kits were applied. Over time I saw oil flooding the timing case at times prevented the Inlet valve receiving an air connection with the crankcase. Oil could then slowly enter the line as the valve was temporarily isolated, till rpm dropped.

A Fresh Approach to the Electra- From our research, clients and test results in 2009 I concluded the strange breathing and oiling phenomenae seen with this engine could be explained if breather flow reversed at high rpm. This follows our breathing paradigm of "different mechanisms at different rpm" This reversal in theory occurs as... 1/ In e/ the oiltank-sump drilling is adjacent the left side flywheel rim. Bell shows a low pressure zone forms around flywheels at high rpm. The sump side of this new drilling has a pressure gradient across it, with higher pressure in oil tank and lower pressure in sump.

2/ As rpm increases blow-by volume falls.

3/ The new Electra four-times gear pump increases sump air scavenging as rpm goes up.

4/ A polytropic process begins in the sump. At high rpm the oiltank drilling becomes restricted by flywheel-adhered oil and a low pressure zone develops. As blow-by falls, scavenge increases as does air flow from sump-to-timing case-to-oiltank...and airflow between the crankcase and oiltank may reverse direction, first during piston upstrokes. Such an event helps explain otherwise inexplicable breather and oiling observations with this engine. We clearly need to change our thinking about breathing this engine.

Some key points are:-1/We regard the timing case as the true oil tank, given Indian design changes.

2/ We see the oil-tank as a sump-extension.

3/ Vent the timing case to atmosphere as its the primary breather path. Also it makes no sense to allow blow-by gas back into the oiltank, once it's been scavenged.         4/ The more gas-flow load we move out of the oiltank, the better the breathing.

5/ Handle the different low-speed/high-speed breather phenomenae by fitting a 'branch-breathe' to the oiltank roof union. The logic is we are forced to breathe out the oiltank at low rpm and into the oiltank at higher rpm. The only way I can see to accommodate these opposing requirements is to use two breather lines and valves on one union. In principle this can function, but the 10mm union available may be inadequate. Road trials are the way forward.

During  February 2011 a new website will publish at www.bunn.co.nz This new site will, like this Blog focus on motorcycle crankcase breathing issues. It will be more user-friendly and  more product-focussed on the Bunn Breather Kits.

This Blog will continue as it contains a unique repository of research and information for all motorcyclists. The new Bunn website will contain links to this Blog and to distributors.

This high-mileage, well-maintained Moto Guzzi 850T has been running an older Bunn kit for about five years. Recently the owner decided to upgrade the breather to our 2010 series Kit. Before doing so, we took the photo below, as it nicely shows the composition of crankcase gases.

The catch-can contains the condensate from 5,000kms running, recently with a lot of short runs. Its in three defined fluid levels or layers. Firstly on the bottom is the major layer of sumpwater (with acids and solids). This is vapourised and pumped out by our breather. Above this is a medium-sized layer of whitish blow-by emulsion. This is an oil-in-water emulsion formed with the aid of other blow-by constituents. The thin top layer is more or less pure oil. This comes from the normal oil mist in the engine, entering a breather union, and being blown out the breather pipe.

NB: in practice the bottom two layers are expelled from the bike as a vapour, usually without leaving any trace or the rider noticing. Any oil mist present may, especially in cold weather condense towards the end of the Draft Tube, leaving a slight residue.

This oil layer is nice and small on this bike, as the owners unions are both custom and in deliberately sheltered places, i.e. one built into the distributor housing and the other in the top of the timing case. The OEM breather unions have been blocked off on this bike, after a lot of road-testing with various breather configurations some years ago.

In reviewing the bike before upgrading the breather, we made an oil analysis and found 0.5% moisture in the hot oil. This is high and helps explain the sumpwater in the photo. Fresh oil has a moisture content of less than half this. At 0.5% moisture levels, water will separate from the oil as it cools and form sumpwater. The oil in this bike was worn and due for a change.

When the older two-valve breather was fitted to this 850T, it pre-dated our research into the role of the oil scavenge pump in engine breathing. The Moto Guzzi engines being wet-sump engines, have only one oil feed pump. This means they cannot breathe out via their oil scavenge pump, like most bikes. We now recognise that Moto Guzzi engines size for size, require more breather capacity than similar dry-sump bikes. For this reason, we're fitting a three-valve breather kit to this engine. As a result we expect the bike to generate less moisture in its oil sump.

Riders often ask me why I don't use EBay any more for Kit sale. This year, I'll try and keep a Kit on EBay for rider buying convenience. As auction numbers change weekly, just do an EBay search for "Bunn Breather" and you should find one availabale.

NB:-The EBay item numbers for Kits from today are:-

1/ Classic Kits-250657864761

2/ Harley-Davidson  Evo Sportster Kits- 250657835489;

NB: POSTAL NOTE--the new 2010 Classic Kit is delivered in new Post Office padded bags. The thickness of the finished pack is a tad over 20mm. This puts it on the borderline between being a Letter or a Parcel. Obviously parcels cost more to post than letters. I have to estimate the kits will be classed legally as parcels (and not Letters) by the post office desk staff BUT sometimes they will pass the bag through a template and send it as a Letter, at a cheaper rate.

There is nothing I can do about this except assure clients this is not me loading up the postal cost. If/when this happens, and if you feel strongly enough, I'm happy to refund riders any gap amount.

For those riders who ask why I don't advertise much in bike mags around the world, or have a glossy website etc...here are some answers below.

I've always regarded this crankcase breather research as primarily a service for riders everywhere. Hence the Kits are priced as service products for direct sale at a low margin. Distributors of course have to add a fair profit margin and cover freight costs etc. That is the way all bike parts are supplied in all countries. I do not chargen them or you, for the years of research that drive new Kit designs. Instead I prefer to spend $;s on road-testing research and quality materials in each Kit.

Sometimes uninformed people have said..." thats a lot of money to spend on a bit of tube and cheap plastic valves". With respect, such comments show the person has no idea about the subject and less idea about the design and manufacture of motorcycle components.

Crankcase breathing is always about holes, tubes, valves and air flow. It;s true you can pay hundreds of $s for breather kits, especially in the USA. Such breathers are expensively made with alloy/chrome casings. These casings contribute nothing to valve function. They are for show. Hidden inside, the moving parts that actually do the work, may be a few cents of rubber. Any rider forking out $X00 for one of these is spending their money on bling, not on a functioning breather.

 I prefer to spend $;s where it counts, on the actual working parts of the breathers and valves; Hencen my Kits use the most expensive materials on the market for their inside moving parts. On the other hand for outer valve casings I work with hi-tech plastics. This saves riders paying for expensive metals tooling and their high factory overheads. My in-line valve casings are practically invisible in service, have an indefinite service life, and can save the rider hundreds of $s. Moreover, they;re transparent so you can check valve function visually without stripping down the valve. No metal valve anywhere offers this convenience.

This design philosophy gives you the best value for your dollar. Thats why I dont offer chrome or metal valves. I do not spend a lot on advertising as that would also increase Kit prices. Many classic bike riders are retired folk and do not have a big budget to spend on crankcase breathing solutions. I prefer the time honoured "walk and talk" method of marketing. My clients refer most of my new clients. Thats the way I like it.

The 2010 Bunn Classic Kit is now shipping. I will try and keep one on EBay this year for easy purchase by riders. Just search EBay for "Bunn Breather" and you should find this Classic Kit and/or  the 2010 Harley Sportster Kit launched earlier this year.  The new Bunn Classic Kit features lsquo;Warm Air Inductionrdquo; and compact, dual air filtration... 

1/ The Inlet air filter is now lsquo;two-stagersquo; i.e. the main American filter comes pre-assembled in the Inlet breather, with a disposable in-line filter screen. The latter helps handle wet country conditions  e.g. in the UK and NZ. Below is a photo showing where to locate the in-line filter. It's an interference fit. I suggest you change the filter during your annual pre-Summer maintenance.

2/ Kits come with a  five-year supply of  spare air filters. The kit is warranted for two years and moving parts for five years, over unlimited mileage. Only top-grade materials are used in the Kits. In my experience,  the Kits last indefinitely.

3/ The Inlet and Exhaust  breathers now come pre-assembled. This saves the rider time and prevents riders installing  a valve the wrong way around. 

4/ The new Inlet assembly is more compact than  previous breather generations, and faster to install.

 5/ The new Exhaust breather assembly includes a lsquo;draft tubersquo; and is pre-assembled to speed installation and obviate installation errors.  

Pictured is a sample 2010 Classic Kit  Inlet assembly showing the components. The green dots mark the course of the Inlet breather assembly. The Inlet terminates over the rockerboxes where it harvests warm air for induction.

Pictured is the new series of Bunn Classic Breather Kits. These are shipping from today. They incorporate the latest research advances made over the past 12 months in Australia and New Zealand. 

Five Key Design Innovations:-

1/ Smaller Installation- the Inlet breather now uses a two-stage air filter system. This is effective while smaller than previous generation kits. It allows more invisible fixing for concours bikes. It speeds installation.

2/ Two-Stage Air filter- the Inlet breather now uses two-stage air filtration. The new main filter is more easily cleaned. The white ‘tube filters’ are disposable and five spare filters are included, sufficient for up to five years of service.

3/ Inlet Pre-assembly- the Inlet breather now comes pre-assembled for even easier, faster DIY installation.

4/ Warm-Air Induction- the new 2010 kits are the first kits purpose-built for “Warm-Air” induction breathing. This assists crankcase pressure control.

5/ Exhaust Pre-Assembly- The Draft tube, introduced late last year now comes pre-installed on the Exhaust valve. This takes the guesswork out of valve installation.

Copyright © A.R.Bunn 2010

 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.

 Copyright © A.R.Bunn 2010

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’.

Copyright © A.R.Bunn 2010

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.

Copyright © A.R.Bunn 2010

  “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. I will try and keep one on EBay this year for easy purchase by riders. The current EBay item number for this kit is 250657835489

These new Kits incorporate three breather assemblies to better breathe the engine. The new mini-filter assembly 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 Exhaust breather assembly installed on the stock air cleaner.

Third, the Exhaust breather valve assembly and Draft Tube.

Fourth, the Inlet breather assembly with "warm air" induction.

For other installation examples, please skip to reports 13 and 37.

Below is shown a stock breather bolt, with typical clips for installing 10mm tube directly onto the bolt.

NB: USA/Canada distribution for this new Sportster Kit is being arranged. Please email me for local ordering details at rexbunn@bigpond.com 

Copyright © A.R.Bunn 2010

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