BMW 'KOMPRESSOR' FOR SALE AT VEGAS

[I'm rarely asked to write catalog copy for Bonhams, but was happy to oblige in the case of this exceptional supercharged BMW, an RS255 'special' built of genuine racing parts supplied by BMW and others, assembled by legendary GP pilot Walter Zeller with BMW mechanic Gustl Lachermair, to campaign in Vintage events.  The following is my description for the upcoming Bonhams sale in Las Vegas]

There is no question the BMW RS255 deserves a place at the very pinnacle of motorcycling history. While the German marque is admired throughout the world for its decades of competent, comfortable, and stylish motorcycling, there was a brief moment when it stood atop the world of road racing as well, having honed 15 years’ development of supercharged Rennsport machines into a thoroughly efficient, reliable, light, and devastatingly fast machine. The late 1930s was a Golden Age of Grand Prix racing, with the motorcycle factories of Europe clashing on newly-built, high-speed racing tracks with supercharged racers of multiple cylinders. Stalwarts of single-cylinder, overhead camshaft development – Norton and Velocette especially – had honed their light and reliable racers since the mid-1920s, with great success, creating the benchmark for an all-around excellent racing motorcycle, which combined light weight, good handling, high speed, and durability for the long-distance races. An amateur rider of great skill could, and often did, win a place in International racing with a machine purchased from these factories. But the ‘Works’ jobs were always that bit faster, and by the mid-1930s, what the factories created for their teams became a completely different animal from what even a favored rider could hope to purchase. And in truth, over-the-counter racers still held a good chance for a win or place, as the big factories were really stretching the limits of technology and metallurgy while testing scientific theories of combustion, supercharging, and aerodynamics.

The RS255 supercharged motor, with Kompressor integrated to the front of the crankcase, and compact DOHC cylinder heads

BMW were among the first motorcycle manufacturers to experiment with forced induction, waiting a mere two years after the marque’s debut (in 1923) to bolt a supercharger to their overhead-valve racing machines.  Perhaps because of BMW’s deep connections with aero engine and auto GP practice, their racing motorcycles were subject to continuous development with ‘blowers’, initially with mixed success in road racing, but which made great account of themselves in the arena of Land Speed Record-breaking.   The World’s Fastest title had, since 1924, been held exclusively by large-capacity JAP-powered English v-twins (installed in Zenith, OEC or Brough Superior chassis), until BMW in 1930 inserted special, Rennsports ‘Kompressors’ into the mix, always with the brave Ernst Henne at the helm.  From that date forward, BMW alternated mostly with larger-capacity English v-twins for the top speed stakes, although a rival Italian marque, Gilera, took top honors in 1937(170.27mph), before BMW snatched the title again later that year (173.68mph),which it retained until 1951.

Ernst Henne with the supercharged BMW WR750 which took many World Speed Records (this from his successful 168.92mph run in 1936)

From that first World’s Fastest title in 1930, considerable development was required before the BMW chassis could compete on even terms with the fleet and nimble English single-cylinder racers.  Great strides forward came in 1935, with the introduction of a recognizably modern telescopic front fork, and the integration of the supercharger at the front of the engine, rather than atop the gearbox as previously.  That blower now sent pressurized air past valves operated by twin overhead camshafts, encased in a remarkably tidy and compact magnesium cylinder head cover. By 1937 BMWs had springing at the rear as well, using a coil-sprung plunger system, with an additional friction damper for the racers to keep the undamped bounce under control.  As the engine dep’t found increasing power, a strict focus on weight control began to pay dividends in handling and acceleration.  The extensive use of magnesium for engine castings and wheel hubs was combined with an ultralight, lugless frame built from lightweight, tapered tubing; elegant, very light, and very strong.   The result of this continual development and improvement was the RS255, which won both the German and European championships in 1938.  A final prize eluded BMW’s grasp, though, as the globe’s attention focused on the Isle of Man TT as the ‘ultimate’ road race, and BMW could only manage 5^th spot at the TT in ’38, with English rider Jock West aboard.

The famous photograph of Georg Meier flying over Ballaugh Bridge in the 1939 Isle of Man TT

The RS255 had been lightened, tuned, and honed into an exquisite racing motorcycle.  It was faster than all its rivals, barring those (AJS, Gilera) with twice as many supercharged cylinders, yet managed to be lightest of all the 500cc Grand Prix racers, fully 30lbs less than its chief rival, the now double-overhead camshaft Norton, which also had its own extensive use of magnesium casings and full springing front and rear.  The two principal advantages of the English marques became the reliability of their engines, and the excellence of their riders.  BMW had an ace up its sleeve in the rider department, as a stout-hearted policeman named Georg Meier had rocketed in a mere two years to the top of the road racing game, after being talent-spotted during a brief off-road motorcycle racing career.  BMW team-mates Jock West and Karl Gall were excellent riders, but lacked the special qualities required of a racing Immortal.  

Jock West aboard the 1937 version of the BMW Kompressor, which used a chassis similar to the BMW R5; a rigid-frame of lightweight tubing, the BMW telefork, full-width hubs, and 'that' motor

Meier wasn’t invincible during the 1939 Grand Prix season, as the four-cylinder, double-overhead camshaft, water-cooled Gilera ‘Rondine’ racked up racing points by sheer blazing speed on the ultra-fast tracks of Europe, winning the European Championship that year.  But the Isle of Man TT still beckoned, which required excellent handling, and a superior rider, beyond mere top speed.  Arriving on the Island early to exploit 14 full days of race practice, the BMW team desperately wanted to prove the superiority of their machines, and pushed hard; member Karl Gall paid with his life, crashing heavily after the notorious ‘leap’ at Ballaugh Bridge.   Despite the loss of their team-mate, Meier and West dominated the Senior TT, with Meier especially smashing lap records from a standing start, and carrying on breaking lap times till the very end, when he became the first non-British rider to win the world’s most difficult road race*.  His victory ensured the RS255’s, and his own, enduring legend.

Lucky bugger Nick Smith of Bonhams aboard the RS255 Kompressor at Willow Springs raceway

After WW2, with Germany, and supercharging, banned from International racing, some ‘blown’ BMW racers continued to circulate in the domestic championships, but complete, and functional, RS255s were always extremely rare.  With the rise of Vintage racing and heritage parades around the world during the 1970s, no example of BMW’s ‘Kompressor’ was available for public demonstration (Meier’s alleged ’39 TT winner sat in boxes in the USA), so former BMW factory racer Walter Zeller asked BMW to parade Georg Meier’s 1950-era RS255, which sat on display at the BMW Museum in Munich.  BMW said ‘no’, but Zeller was persistent in his desire to show the legendary machine on the track; he knew the BMW factory still possessed a considerable pile of early racing parts, and in 1980 he began assembly of a 1951 Rennsport ‘plunger’ frame with a genuine 1939 RS255 engine. Gustl Lachermair, the BMW engineer who was responsible for servicing racing engines all through the 1950s-70s (and who rebuilt almost all RS engines after retiring from the factory), built the engine to 1949/50 specification, with a bigger supercharger than used in ‘39. The 1951 chassis has a strengthened frame, and the leading axle teleforks are very similar to the type used by BMW in 1949-50.  Zeller modified the front brake for twin-leading shoe action, and used clip-ons instead of the ‘39s flat aluminum handlebars.  The rear wheel was built with a 19” rim instead of 20”, as no new tires of that size were available.

From Classic Bike magazine, June 1985; Walter Zeller, Gustl Lachermair, and Stefan Knittel discuss Zeller's RS54 and RS255 Kompressor

Zeller and Lachermair used mostly original, factory racing components, which they accumulated from BMW factory stock or private contacts. BMW understood this machine to be Walter Zeller’s private project, and gave him the parts, which might seem less remarkable today, knowing the BMW factory had previously presented Zeller with a factory-built, road-going supercharged ‘special’ in appreciation for his 2nd place in the 1956 Grand Prix World Championship. In the end Walter Zeller became the official owner of the completed motorcycle. The BMW factory kept no records of racing engine and frame numbers from the prewar era, and there exists no related information correlating to race entries, riders or results. It is therefore impossible to state with certainty the race history of the engine or chassis of this motorcycle, only that the components are nearly all genuine BMW ‘factory’ racing parts, assembled by two legendary figures in BMW history - racing champion Walter Zeller, and engine builder Gustl Lachermair - and paraded by Zeller in Vintage events from the 1980s.

(*The Senior TT.  Of course, Omobono Tenni was the first 'foreign' rider to win a TT)

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