The crankcase breathing of classic motorcycle engines is a subtle and neglected subject. Early motorcycle designers spent more time on what was happening over the , than under it. Little has changed on today's marques. These feature the same problems as those with vintage and classic engines. Rex Bunn, developer of the Bunn breather technology, shows us how gains can be made to engine power, oil-tightness and service life by making simple improvements to crankcase breathing.

So just what is crankcase breathing7 competition engines with altered In four-, classic singles, vertical and timing, OEM breather settings may no twins, vee twins or boxer engines; air longer apply. For competition engines rushes into the crankcase as the piston blow-by volume can ramp up at peak revs descends. More air escapes past the from ring flutter and a timed breather be piston rings into the as 'blow-by found wanting. Classic designers often vapour' and some passes up the valve designed crankcases to operate with a guides into the rockerbox. This air small vacuum, as they tried to control oil water, sulphur compounds, nitrogen compresses and pressures rise as the leaks. Some classic breathers didn't work oxides and soot. Oxides of nitrogen fc crankcase is closed. These 'pressure when new or now. We can improve on under the high temperatures and spikes' worry away at and seals them with new breather technology to pressures in our air-cooled engines, i and force through joints, unions and keep these engines working more temperatures reach 160C-23C porous castings. The crankcase is vented efficiently, while purging blow-by, and versus engines at half lhat. The to let some of this gas escape via cutting oil leaks. hydrocarbons, nitrogen and sulphur breather tubes... at least that's the theory. compounds form a corrosive mixture New Developments an "acid rain" inside our engines. This OEM My research shows while oil leaks are a emulsifies with engine oil and sumpv Biitish makers vented their engines with sign of breathing problems, blow-by gas giving that white fluid in breathers. open tubes, clack and flapper valves or inside the engine is a more serious long- Letting ibis stay in the crankcase is timed breathers. A timed breather is good term issue. For many riders blow-by gas is spraying battery acid around inside a at cutting return flow, but not so good at a blind spot. It's almost as if exhaust watching your engine rust. passing volumes of air versus eg. the open gases, which we rightly see as nasty in Blow-by causes many problems. Tl breathers on Triumph or BSA twins and the and exhaust include oil dilution and contamination singles. A typical British timed shaft pipe... somehow become acceptable once sludge, loss of oil film, corrosion, cr, breather has a bush aperture of approx. they slip past the rings... and even safe to fire risk and rubber deterioration. As f RF10W 3/16" and a circumference of approx. 3/4. mix with our oil. Irving noted approx. 5% unburn: v: Harley-Davidson breather. That means the holes overlap for only In reality it's like storing your engine oil the sump can reduce oil viscosity to I BELOW BIGHT approx. 8°/o of shaft rotation, and are than 25%. Classic engines are also p Independent dyno test from inside your exhaust pipe. USA shows a 6bhp gain and superimposed for a fraction of that. Not Blow-by gas isn't benign, inert stuff. It's to sumpwater. I find 20-5umls in cl< increase in torque. much blow-by gets out. In older and approx. 70% unburnt flammable fuel, if breathing is neglected. A

Horsepower is Adjustable

II Illinois Harley-Davidson/Buell Sales Inc. 1301 S. Harlem Ave. Berwyn,

IV. . OLD BIKE AUSTRALASIA : 19 FH

of thumb Irving set 0.1% for maximum Car PCV Breathers moisture in oil. In a typical classic that's These are a classic waste of money. Since approx. 2rnls of water. Today's engine oils WWII have used a recycling system average 0.2% or twice that. Worse, I see with PCV (Positive Crankcase Ventilation) engines with five to ten times that valves. Car engines are different. They are amount, and as sumpwater. No wonder multi-cylinder engines where the big wet they need frequent rebuilds! sumps and barrels act as surge chambers. At these levels, clouds form in the While there's air turbulence, there's less air crankcase, and rise into the rockerbox displacement in and out of the crankcase where it literally rains. v's classic bikes. Car PCV valves are both As well as oil leaks and blow-by non-return valves and metering devices. damage, my research shows poor PCV valves have a flow rate for a make breathing causes power losses in our and model. Its luck if one matches a clas- engines. This is due to drag and the sic bike. As well, they're designed to work piston(s) wasting work by pumping air in in a cooler, cleaner place with an the crankcase. Charles Falco* noted a vacuum, not the hot, dirty, pressured bike decade ago lhat "...the piston, which has crankcase. At high rprn they hold open a suiface area of approx. 9 sq. in. in tfie and are of no use as valves at all. Car case of a SOOcc, would have to travel the breathers, along with modern bike entire length of its stroke against a force systems, are more about emission of appiox. 130 pounds (9x14.7-132lbs)." compliance lhan engine operation. He predicted an exlra 10% or roughly They have no place on classic bikes. three free bhp might be gained from a SOOcc engine, if breathing could somehow Fire Risk with Breathers be optimised. A decade later, Australian Where breathers recycle blow-by into the researchers achieved this. On the first inlet tract, a flame path opens to the independent dyno tests with a Vincent crankcase. Classic crankcases fill with and Bunn brealher, such gains in bhp and flammable gas at times like a two-stroke. torque were recorded. The Harley- Recycling without a flame barrier invites a Davidson engine records similar gains. crankcase lire, if an engine backfires. Re- breather designs, our engines generate a The Bunn Breather fitted feeding blow-by also dilutes the charge, blow-by velocity of approx. 1 meter/sec. to a current model Classic Breather Faults (TOP) Royal Enfield and interferes with pressure, fouls the This is a 'very light breeze' on the All breathers are compromises. Open (ABOVE) Vincent v-twin. carburetter and impacts on engine Beaufort scale. breatheis waste power, contaminate temperature and pressure at high revs. It (D) Cycles from 1-6000+rpm - The typical compartments and admit dirt. Valves stick can affect combustion and even fuel range on road and track for classic and malfunction in the filthy conditions. choice, acting as an octane booster. After engines. As peak blow-by generates every Tubes clog with emulsion, leading to relieving poor breathing, engines may fourth stroke (or second revolution); pressurising, oil loss and seizing. Later need tuning and/or higher octane fuel. valves need to operate at half engine rpm British designs worsened blow-by The ideal Breather Valve or sometimes less, depending on the problems, so bikes could pass emission aerodynamics. tests, l hey re-cycled blow-by into the oil The new Bunn Breather technology (E) Minimal weight - The ball, disc or flap tank, timing chest or chaincase... satisfies the following requirements for must be light. The lighter the better at anywhere but outside the engine where it a classic breather valve. high speeds. Spring valves often fail this 1 could be detected I his lemedy contained (A) Opens and closes at low pressures - hurdle. emissions, but spread corrosive blow-by Our engines generate very low air (F) Works at lean angles - Car valves stay over points, Boyer, alternatoi, clutch and pressures when breathing properly. Valves upright and when tilted, bind or alter chain. It denatured oil, and pressurised oil must open and close with very little performance. This is no good on a heeling tanks. These problems afflict triumphs, pressure gradient..This excludes many bike! Mortons and BSA's. valves sourced from industry eg. plumbing (G) Optimal performance over the range On today's bikes the same problems are valves designed for a hundred times our of bike crankcase pressures - the normal seen in eg. Moto-Gu/zis, Royal bnfields pressures and for water, not gas-aerosol pressure range is 700-820mmHg. and Hailey-Davidsons. Their re-cycling mixtures. (H) Good sealing - Unless the valve is breatheis also sacrifice engine function (B) Handles low air flows - It's a designed to seal at very low pressures, it and service life, to satisfy emission misconception 'more breathing is better'. may leak. This involves the materials Charles M. Falco requirements. From the viewpoint of In fact our engines don't pass much air technology of mating surfaces where eg. University of Arizona (1997- crankcase breathing, this is poor design. when bieathing properly. Only 2-10 litres Harley-Davidson and Royal Enfield fall present), UA Chair of Condensed Foi Innately classic engines face no per minute are required to breathe a 500- down. Matter Physics and Professor of Optical Sciences. He was notably emission requirements. We can optimise 1000cc engine. Big breather tubes are (K) Copes with sun and weather exposure, co-curator of the Guggenheim breathing to preserve these engines for unnecessary heat, fuels, methanol, oils, water, blow-by Museum's 'The Art of the the next generations. (C) Handles low air speeds - With the new acids, soot etc. >• Motorcycle' exhibition. 20 : OLD BIKE AUSTRALASIA 1 - KG 5 ." ' ' -JNG

(L) A long service life - ideally years. blow-by gas. Bum* i£chnoi. jn iiK'irn r.ii&mcs h'> ca>>-to fil. (M) Serviceable - the valve must be easy \eaks and (wimps out teiic bk>w by to open, inspect and clean. Valves operate warranted fa five yem over unltm in filthy conditions. It's unrealistic to 2 1 One Bunn Intel i ah c. Uh: wi expect them to operate without an 2.2 Ore Bunn fcxtiaust %«!«. \D« 2.3 IV V;SCE Ouirlc. a stcp-by-SS occasional check. Some US manufacturers 2 4 Tut>m£- 5t^)tnni eaeli of ^rra 2.5 One tiigh-tlo* l-Smtcrooai make no provision for this. 2.6 Carte) card. Please raain to (N) Transparent Housing - Seeing inside 2.7 Cable tto in » range of"» 2 8 Spring tubing damns to SI the valve lets you check it. It helps 2.

diagnose engine problems along the road. >,.,,,!»!.!njJ!!«B»a£S>ftE ^nncctcd .-(mipanmctlts i.e. rod I his is a particular feature of the new 00 Mpumpuifietwo' ^ Bunn breathing technology. typical -Top^^*11 (0) Low maintenance - Inspect and clean 3.1 breather, b once a year. (P) Reasonable Price - Classic riders will Irtlap « in10 you"™*5' not pay S200 for US chromed breathers tdsRanswWlhchatclKO that are often just catch-cans. Wb»c.« a sheltered sp< (fl Secure filtamfBi™ (Q) Invisible - For classic and concours ) Insert valve t bikes, modern parts are hidden. aiTO* pointing Ili' (R) Bolt-on - Classic riders want an easy, fast install. ' Before (S) Cuts power losses - Power and torgue ,,fflm- gains are welcome. Pre ;ather val BS enow One group of valves performs best in Owners of later Triumph and classic bike breathing, and has been used BSA twins and singles find a since pioneer days. These are based on MIG diffuser makes a fine human heart and leg vein valves. They union for the timing plug. include... (A) Flap valves - these operate on a hinged-flap principle and include 'reed (B) Ball or Disc valves - where a ball or Nortons or BSAs the Bunn breather form valves' in outboard motors and two disc seals against a seat eg. Moto-Guzzi. a blow-by extraction system. Properly strokes. Sometimes the hinge is replaced designed and balanced, it foirns a doubli by a spring as in Matchless and AJS. The How and where to acting air-pump in the crankcase. Exhaus Harley-Davidson umbrella valve is a flap breathers are connected, often via the valve, as are valves in respirators and connect breathers? crankcase. A filtered Inlet breather is duckbill valves in Royal Enfields. Our fathers made little provision for connected via eg. the rockerboxes. Over breathing, but it's possible to fit improved successive strokes blow-by is evacuated breathing to nearly every classic and as Ihe breather takes over the crankcase vintage bike. Unions can be formed from the exhaust and Inlet breather airflows a range of existing covers and drillings, are balanced to ensure the crankcase avoiding permanent alterations. Access is never again pressurises. gained via timing plugs, rev-counters, This has a number of benelils for class valve-lifters, OEM breather unions, rideis. It reduces crankcase pressures ar rockerbox hatch-covers, inspection covers swings to cut oil leaks. It purges blow-t or filler plugs. The latter can be replaced and sumpwater, preserving engine oil for concours. Owners of later Triumph and viscosity while cutting wear and conos'. BSA Iwins and singles find a MIG diffuser to extend engine service life. It creales I makes a fine union for the timing plug, as unidirectional airflow that reduces shown in the illustration at left. entrained oil, foaming and oil venting ar New breather technology cuts oil drag and power losses. The nev. technology is versatile, wilh a series of Australia leads the world in new classic around 700 bikes to date, covering das; motorcycle breathing advances. In the British and American marques. • new Bunn breathing technology, valves are grouped and balanced to achieve Readers wishing to correspond on : target figures for crankcase pressures, breathing or the new Bunn breather blow-by flow and velocity. technology can email Rex Bunn on For Vincents, Enfields, Harleys, Triumphs, [email protected]