BMW R51/3

The BMW R51/3 was BMW's second post-World War II 500 cc motorcycle, following the briefly produced R51/2. It featured a flat-twin engine and exposed drive shaft.[1] In 1951, the R51/3 succeeded and modernized the 1950 R51/2, which was essentially a pre-war design that was produced after the war. The 600 cc R67, R67/2, and R67/3 series and the more sporting R68 model also followed the R51/2.

BMW R51/3
A 1952 R51/3 – note the half-width brakes before 1954
ManufacturerBMW
Production1951-5
Engine494cc four-stroke flat-twin
Bore / stroke68 mm
Compression ratio6.3:1
Top speed140 km/h
Power24 hp
Ignition typeMagneto
TransmissionSingle-plate dry clutch, 4-Speed manual
SuspensionFront telescopic forks, rear plunger
Brakes200mm drums
Wheelbase1400mm
DimensionsL: 2130mm
W: 790mm
H: 985mm
Weight190 kg (wet)
Fuel capacity17 L
Oil capacity2 L
Fuel consumption4.5L/100KM
1951 R51/3 at the BMW Museum
1955 BMW R67/3
An R51/3 has eight round cylinder fins (left); the R67-R67/3 have nine larger and pointed cylinder fins (right)
Note the exposed driveshaft and plunger rear suspension

History

Following World War II, Germany was precluded from producing motorcycles of any sort by the Allies. When the ban was lifted, in Allied-controlled Western Germany, BMW had to start from scratch. There were no plans, blueprints, or schematic drawings. Company engineers had to use surviving pre-war motorcycles to create new plans. In 1948, it introduced the 250 cc R24, which was essentially a pre-war R23, complete with rigid rear end.

When larger machines were permitted, BMW introduced its R51/2 in 1950, a model that was in production for only one year and that was essentially a pre-war BMW produced after the war. The R51/3 was then introduced in 1951 for a production run of four years.

The 600 cc R67, sister model to the R51/3 and almost identical visually, was also introduced in 1951, but it went through two revisions. The more powerful R67/2 came out one year later and was replaced in 1955 by the R67/3, which was in production through the 1956 model year.

In 1952, BMW introduced the 600 cc R68,[2] which produced 35 hp (26 kW), had a compression ratio of 8.0:1.

Technical data
Front view of an R51/3
R51/3 R67 – R67/3
Design Boxer Flat Twin
Engine Four-stroke OHV
Model Years 1951–1955 1951–1956
Bore 68 mm / 2.68 in 72 mm / 2.83 in
Stroke 68 mm / 2.68 in 73 mm / 2.87 in
Displacement 494 cc (30.1 cu in) 594 cc (36.2 cu in)
Power 24 hp (18 kW) @ 5800 rpm 26 hp (19 kW) / 28 hp (21 kW) @ 5500 rpm
Compression Ratio 6.3:1 5.6:1 / 6.5:1
Top Speed 140 km/h (87 mph) 150 km/h (93 mph)
Curb Weight 190 kg (419 lb)
Gross Vehicle Weight 355 kg (783 lb)
Fuel Tank Capacity 17 L (3.7 imp gal; 4.5 US gal)
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See also

References
  1. "R51/3 data sheet". Archived from the original on 2014-10-31. Retrieved 2012-07-05.
  2. "BMW R68 Data". Archived from the original on 2014-08-08. Retrieved 2012-07-03.

Media related to BMW R51 at Wikimedia Commons

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