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From CycleChaos
1927 BMW R47

BMW's first sports model, the BMW R37, appeared in 1924, joining the original BMW R32 tourer. The BMW R37 boasted a new overhead-valve engine producing 16bhp, almost double the R32's power output, but was produced for little more than a year before being replaced by the improved BMWR47. The latter was introduced in 1926 alongside the sidevalve-engined R42 tourer, both models benefiting from a redesigned and more powerful engine boasting detachable alloy cylinder heads and cooling fins set at 90 degrees to the cylinder axis. The engine was set further back in the duplex loop frame, which improved weight distribution and enabled straight front down-tubes to be used. The braking too came in for attention: the old block-and-pulley type rear brake being replaced by a drum on the driveshaft gripped by external contracting bands. Electric lighting was still regarded as an 'extra' and would not be standardised until 1928. Maximum power output of the R47 was 18bhp and its top speed in the region of 70mph (113km/h). R47 production lasted for just two years, 1,720 machines being sold.