Bmw R1
Years before Yamaha, BMW was developing an R1 superbike of its own
BMW R1
KEVIN CAMERON
CONSIDER THE PLIGHT OF BMW. In the car world, its products are considered racy and exotic while its motorcycles are seen by some as staid two-wheeled Volvos. Cadillac would love to have BMW's four-wheeled image, which is why it’s going racing at Le Mans. Would BMW like to attract sportbike buyers? Why do BMW motorcycles lack the sporty image of its cars?
These questions have obviously been asked at BMW. Not only does the German company compete in the African Dakar Rally, it evaluated this fascinating prototype liquid-cooled desmo Boxer Twin back in 1990.
Where traditional BMW HatTwins locate their accessories above the engine, this R1 prototype flips that relationship to achieve a huge gain in cornering clearance. Even with the crankshaft centerline thus almost 20 inches above the road, the exhaust camshafts of this dohc four-
valve-per-cylinder design are placed closer to the pistons to give the heads a “beveled” aspect that further increases lateral clearance.
The engine is water-cooled, with a pair of radiators located in flow-through ducts below the rider’s hands. This system is apparently effective, because the total radiator area is small. The 98 x 66mm engine gives 996cc displacement, the same numbers used by Ducati and its emulators.
Suspension is by BMW’s proven Telelever/Paralever systems, but the chassis is pure sportbike, consisting of twin aluminum spars.
Cam drive is by four chains, taken from a half-speed idle shaft beneath the engine. Each main chain drives one cylinder’s exhaust camshaft, while a short second chain connects exhaust and intake cams. Remarkably, BMW chose to use desmodromic valve actuation on the R1. Mercedes-Benz used a related system on its W-196 GP car of 1954 to overcome problems with valve spring breakage. Ducati has continued to this day with desmo valves, despite the development of satisfactory valve springs. Why bother with desmodromics? High performance is clearly not the reason-today’s 18,000-rpm Formula One racecar engines use conventional cams with gas pressure taking the place of metal valve springs. That leaves only the attraction of idiosyncrasy, of an ingenious mechanical alternative. This fits well with the Boxer engine concept.
Traditionally, BMW’s Boxer positions its intakes behind the cylinders and its exhausts ahead. In the Rl, with its abundant ground clearance, the cylinders exhaust downward while the intakes feed in from above. This eliminates the traditional BMW problem of how to find room for both the intake system and the rider’s feet. Bosch fuel-injection stacks connect to an airbox concealed under the “fuel tank,” and served by slots in the fairing nose.
The combustion chambers reflect BMW’s experience in this area, and are more modem than the deeper chambers in the current 916/996 Ducati. Difficulties with the exhaust bridge (the narrow mass of material between each pair of exhaust valves) in the air/oil-cooled production Twins have resulted in these exhausts being widely separated. Included valve angle is small (not much more than 20 degrees), so the very shortskirted pistons have flat tops, featuring only slight valveclearance cutouts. To hedge against possibly slow combustion, the Rl’s heads are cored for three spark plugs each-a conventional central plug and two side plugs. On the example shown, the side plug positions are blank. The same arrangement can be found on BMW’s Formula Two auto-racing engines of the 1970s.
The longer I looked at this prototype, the more I asked myself this question: How much must a company do to uphold its historical tradition, and when does that tradition become useless baggage? Pontiac got rid of its chrome hood and trunk stripes, and Buick ditched its signature portholes, after all. The good reason for Max Friz’s 1923 BMW Boxer design is that it put the air-cooled cylinders out in the free air stream for equal and maximum cooling. But this R1 engine has liquid cooling. What are its cylinders doing sticking out to the sides in a style that dates back to the Weimar Republic?
They are doing two things: (1) satisfying traditional insistence that all BMW Twins be Boxers; and (2) providing good primary and secondary balance.
Planners at BMW surely made this same list, and decided that the reasons didn’t add up. The R1 was not produced.
