1956 BMW Rennsport RS54 with 'Bartl' Fairing
Chassis no. 256014
Engine no. 549014
With 19 World Sidecar Titles and significant Grand Prix success in the 1950s, the BMW Rennsport is a technical tour-de-force, and the ultimate expression of a BMW one could actually purchase from the factory. While roadster BMWs through the late 1960s could be fast and reliable sport-touring machines, devotees of the German marque with more heat in their veins have always lusted after the RS54 as the only flat-twins able to hold their own against the very best of its British and Italian rivals.
What made the machine so good? For a start, the chassis was state of the art, being lugless and of all-welded construction, from lightweight oval-section tubing. The rear swingarm housed the driveshaft aft of its four-speed gearbox, which was itself a very compact casting, shaped to mate with the crankcase. The front forks were a design patented in 1953 by an Englishman, Ernie Earles, whose design was very light and much stronger then telescopic forks, being fairly proof against deflection during hard cornering while racing, most especially when racing a sidecar. The fork was considered good enough for GP rival MV Agusta, who experimented for many years with the Earles design on their single- and four-cylinder racers during the period BMW raced with them as well. While BMW's roadsters would adopt an all-welded chassis with oval tubing and Earles forks in 1955, the RS chassis was a fraction of the weight of their road-legal cousins.
The RS engine differed significantly from roadster practice, and not merely in the adoption of twin overhead camshafts. The pressed-up crankshaft ran in 3 main bearings, the rear utilizing barrel-shaped rollers to accommodate any radial flexing of the crank while under the tremendous forces of acceleration and deceleration. The crankshaft lubricated its big end bearing through a clever set of grooves and 'slingers', to obviate the potential weakness of a crankshaft drilled with oilways. The main bearings sat within cast housings, which were bolted into the crankcases; the front bearing holder also housed a twin-gear oil pump, which fed from a 2.8L sump. The front of the crankcase housed a gear-drive timing chest, which drove the magneto atop the engine, the tach drive, and the oil pump. The cylinder barrels were aluminum, and some RS54s had plated cylinder barrels rather than a shrunk-in liner. The entire cam drive, camshaft, and rocker system ran in needle rollers. The twin-cam system is different from any other DOHC setup, utilizing a drive shaft to turn the exhaust camshaft, which is geared to turn the inlet cam. Rather than extend the cam drive assembly further from the center line with a typical '5-gear' DOHC drive, the two cams sit between the valve stems, and use short rockers (on a 1:1 or 'flat' ratio) to push the valves open. The overall effect of this clever and compact arrangement was a cylinder head scarcely taller than BMW's pushrod engines; essential to prevent 'grounding' of the protruding cylinders while racing. The overall weight of this impressive racer was a mere 160kg (286lb).
This BMW RS54 with distinctive Bartl-style 'duckbill' fairing, bears engine and chassis #549012, which has been modified with a short-stroke (75x72mm) crankshaft, using 9.8:1 compression pistons in 'Nikasil' plated aluminum bores. The inlet valve is 42.5mm, the exhaust 38mm, and carburetion is by 35mm Dell'Orto SS1 instruments. The cylinder heads bear twin-plug ignition (as used on the late Works machines), with sparks generated by an alternator and coils. The oil sump is magnesium, and the tachometer (Smiths 12k rpm 4:1) is spun by a 90 degree drive at the timing chest. The gearbox is a 5 speed, connected to a 'Works'-type exposed drive shaft. The front brake is an RS54 twin-leading shoe, while the rear brake is a later hydraulic drum as used especially on sidecar racers.
According to documents supplied by Mr. Bern Staschel of Bremerhaven, Germany, 'This machine was assembled in the 1970s largely from original spare parts, by Mr. Freidrich W. Staschel. Since 1984, Bern Staschel raced this RS54 at many German national and international vintage racing events.'