BMW's first sports model, the R37, appeared in 1924, joining the original R32 tourer. The 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 R47. 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, and today this rare BMW is among the marque's most desirable and sought after machines of the Vintage period. The machine offered here consists of the frame from an R42 (delivered to Leipzig in March 1928) and an R47 engine, and is equipped with a Bosch electric lighting set and UC6 horn, and a reproduction auxiliary fuel tank. Die hier offerierte Maschine von 1927 besteht aus dem Rahmen einer im M�rz 1928 nach Leipzig ausgelieferten R42 und dem Motor aus einer R47. Sie ist mit Bosch Beleuchtung und einer UC6-Hupe, sowie einem reproduzierten Reservetank ausgestattet.
Engine and transmission | |
| Engine type: | 2 cylinders, 4-stroke, Boxer |
| Displacement: | 494 cc (30.18 cubic inches) |
| Bore × stroke: | 68 mm × 68 mm (square) |
| Cooling system: | Air cooled |
| Power: | 11.96 HP (8.8 kW) @ 3400 rpm |
| Throttle: | Cable operated |
| Valves | |
| Valve train: | OHV, variable |
| Valves per cylinder: | 2 |
| Fuel and ignition | |
| Sparks per cylinder: | 1 |
| Fuel supply system: | Carburetor |
| Funnel diameter: | 22 mm |
| Compression: | 4.9:1 |
| Engine mounting: | Longitudinal |
| Lubrication system: | Wet sump |
| Gear box: | Manual 3-speed |
| Clutch: | Dry, single plate, cable operated |
| Final drive: | Shaft |
| Spark plug pipe type: | Bosch, W 175 |
| Starter: | Kick-starter |
Dimensions | |
| Physical measures | |
| Length: | 2100 mm |
| Width: | 800 mm |
| Height: | 950 mm |
| Wheel base: | 1410 mm |
| Weight | |
| Curb weight: | 126 kg |
Chassis and suspension | |
| Frame type: | steel, Double cradle frame |
| Front | |
| Suspension: | Leading link |
| Brake: | Single Drum, Ø150 mm |
| Tire: | 3.5 × 26 |
| Rear | |
| Tire: | 89 / R26 |
Other | |
| ABS available: | No |
| Power-to-weight ratio: | 0.07 HP/kg (14.32 kg/HP) |
| Top speed: | 95 km/h |
| Fuel capacity: | 14 l |
| Number of riders: | 2 persons |
