BMW_R51/3 Knowpia

BMW R51/3
	A 1952 R51/3 – note the half-width brakes before 1954
Manufacturer	BMW
Production	1951-5
Engine	494cc four-stroke flat-twin
Bore / stroke	68 mm
Compression ratio	6.3:1
Top speed	140 km/h
Power	24 hp
Ignition type	Magneto
Transmission	Single-plate dry clutch, 4-Speed manual
Suspension	Front telescopic forks, rear plunger
Brakes	200mm drums
Wheelbase	1400mm
Dimensions	L: 2130mm; W: 790mm; H: 985mm;
Weight	190 kg (wet)
Fuel capacity	17 L
Oil capacity	2 L
Fuel consumption	4.5L/100KM

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.

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 edit

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 edit

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)

References edit

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