BMW R 51 – year 1938
Manufacturer: Bayerische Motoren Werke AG, Munich, Germany
BMW R 51 is one of the company's strongest touring bikes, also suitable for driving with a sidecar.
It was powered by a two-cylinder boxer engine, mounted in a triangular frame made of steel tubes. From the displacement 494 cm3 (piston stroke and cylinder average - po 68 mm) maximum power reached 18 kW (24 KM) at 5400 rpm. Valves, located in the engine head and equipped with snap springs, were controlled by two camshafts. The fuel-air mixture was being prepared, separately for each cylinder, in two Amal carburettors. A four-speed foot-operated gearbox locked with the engine was standard equipment (it was also supplied with a coupled manual gearshift system). The drive from the box to the rear wheel was transmitted by a shaft with articulated joints and a main gear with helical gears. Vehicle wheels, interchangeable, they were equipped with mechanical brakes with large diameter drums. Chassis with telescopic front wheel suspension, and (for the first time at a BMW) rear wheel, was also used in the R models 61, R 66 i R 71. Other design highlights of this model included an adjustable saddle and steering wheel, and in the first series also a telescopic fork with adjustable flexibility. All elements of the electrical installation: ignition (battery type) and lighting (with a reflector equipped with a speedometer) and the electric horn came from Bosch. The factory served, that this mighty motorcycle, weighing 182 kg, consumes 4,5 1/100 km when driving solo, a 6 liters / 100 km when loaded with a sidecar. The maximum speed is set to 135 km/h. In the years 1938-1940 it was produced 13 000 pieces of this model (it was the most popular model in the entire series, to which also belonged R. 61, R 66 i R 71).
BMW R 51, after making minor changes, were still produced after the war – as type R. 51/2 – in years 1950-1951 and as type R. 51 /3 w 1955 year.