BMW R 4

The BMW R 4 was a single-cylinder BMW motorcycle of 400 cc that appeared in 1932. BMW had no successor for the 500 cc R 52, so it brought out the R 4 with the same power as a cheaper middle-class machine, placed between the tax-free R 2 and the 750 cc twins, at the difficult time of the world economic crisis. Series production began in December 1931 and BMW offered it as an off-road sport model at 1250 Reichsmark, a price cut to 1150 from 1933 until production ended in 1937. The upright cylinder had a fully enclosed valve train with overhead valves and made 12 horsepower, and drive went to the rear wheel by shaft.