BMWR51 1938 - 1940

　　In 1938, BMW released the R51, which took the complex engine with two camshafts driven by a timing chain, almost unchanged from the model it replaced, the R5.

　　The R51 model featured a 494cc air-cooled, four-stroke, boxer twin-cylinder engine with a power output of 24 hp at 5,600 rpm and a top speed of 140 kph (86 mph). The R66 model produced six hp more and was also five kph faster than the R51 in terms of speed, but the 1938 BMW R51 model offered excellent handling with its agile engine and low weight of 182 kg (401 lbs).

　　Also, the R51 was the base model for two competition versions such as the R51 SS (Super Sport), with four hp more and a top speed of 160 kph (99 mph), and the R51 RS (Renn Sport), which had a completely redesigned engine with a power output on 36 hp and a top speed of 180 kph (111 mph).

　　The R51 model featured a cradle tubular steel frame, a telescopic fork with a hydraulic damper on the front, and a telescopic suspension on the rear.

　　The brakes consisted of a 200 mm drum unit on the front wheel and a 200 mm drum unit on the rear wheel.

　　As standard features, the bike came with a single seat, a rear luggage rack, a large headlight, a dual exhaust system, laced wheels, and full fenders.