BMW R 51/3

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R 51/3 right side

The BMW R 51/3 was BMW's first modern postwar 500 cc motorcycle. It used BMW's time-tested boxer engine layout and exposed driveshaft. The R 51/3 succeeded and modernized the 1950 R 51/2, which was essentially a prewar design that was produced after the war.

1 History
2 Technical data
3 Gallery
4 See also
5 External links

[edit] 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 Aktiengesellschaft (AG) had to start from scratch. There were no plans, blueprints, or schematic drawings. Company engineers had to use surviving prewar motorcycles to create new plans. In 1948, it introduced the 250 cc R 24, which was essentially a pre-war R 23, complete with rigid rear end.

When larger machines were permitted, BMW introduced its R 51/2 [1] in 1950, a model that was in production for only one year and that was essentially a prewar BMW produced after the war. The R 51/3 was then introduced in 1951 for a production run of four years.

The 600 cc R 67, sister model to the R 51/3 and almost identical visually, was also introduced in 1951, but it went through two revisions. The R 67/2, with 2 hp (2 kW) more, came out one year later and was replaced in 1955 by the R 67/3, which was in production through the 1956 model year.

In 1952, BMW introduced the 600 cc R 68 [2] [3]. With 35 hp and a compression ratio of 8.0:1, this was the first BMW production motorcycle that could reach and pass 100 mph (160 km/h).

[edit] Technical data

The engine of the R 51/3's predecessor, the 1950 R 51/2, had an exposed generator, no magneto, and split valve covers

Compare the clean, unit-cast R 51/3 engine above to that of the R 51/2 above

	R 51/3	R 67 - R 67/3
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 in³	594 cc / 36 in³
Power	24 hp	26 hp / 28 hp
@ RPM	5,800	5,500
Compression Ratio	1:6.3	1:5.6 / 1:6.5
Top Speed	87 mph (140 km/h)	93 mph (150 km/h)
Curb Weight	419 lb (190 kg)
Gross Vehicle Weight	783 lb (355 kg)
Fuel Tank Capacity	4.5 US gallons (17 litres)

[edit] Gallery

1952 R 51/3 left side: note the half-width brakes	R 51/3 plunger and exposed drive shaft	R 51/3 "bell-bottom" front fender	1951 R 67: note the rigid sliders on the front suspension, later to be replaced by rubber gaiters
Disassembled R 51/3: note the full-width brakes from the last year of production	R 51/3 identification plate	Opposed cylinders on a 1954 R 68	The rare R 68: BMW's first 100 MPH motorcycle

[edit] See also

[edit] External links

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