BMW 1941 R66 597cc OHV horizontally opposed twin project frame & engine # 662024 The 1940 BMW twin range consists of four models: two side valve machines, the 600 cc R61 and the 750 cc R71, and two ohv machines, the 500 cc R51 and the top model, the 600 cc R66. All engines are interchangeable and share the same transmission ratios, the final drive ratios can vary. The 597cc engine with bore and stroke of 69.8 x 78 mm has a compression ratio of 6.8 : 1 and a power output of 30 hp @ 5300 rpm which ...