The photo below shows a 1953 R51/3 restored beautifully by Tim Stafford for auction in 2007 at the MidAmerica Motorcycle Auction in Las Vegas, Nevada.

The image below shows the original R51/3 in the BMW brochure of 1952.

The photographs below show Craig Vechorik's 1950 BMW R51/2, the precursor of the 1951 R51/3. Notice the differences in the -/2 and -/3 engines. The older engine has an exposed generator, as well as other exposed parts, and a two-part valve cover. The air cleaner housing was much increased in size after the -/2. Like the R25 through R27 BMW singles it had battery ignition — no battery, no go. The -/3 has a much cleaner design, a unit-cast engine and magneto ignition. The R51/2 came with no brake light, nor did the first R51/3 models. In time, however, the R51/3 corrected this by adding one.

R51/3 data from the BMW Historical Archives in Munich

Production period: 1951 - 1954
Power output: 24 PS bei 5800 U/min
Maximum speed (km/h): 135
Displacement (ccm): 494
Engine: flat-twin engine
Price: 2,750 DM
Units: 18,420

At the Amsterdam Show in February 1951, BMW had two motorcycle models with new engines on display: the 500-cc R 51/3 and the 600-cc R 67.

In contrast to the first post-war flat twin with its two chain-driven camshafts, there was now a single central camshaft driven by gearwheels from the crankshaft. The engines were handsome designs with smooth surfaces and one-piece valve covers. Placing the magneto and the generator behind the front cover made the engines more compact. The new Noris magneto ignition with automatic advance and retard enabled the engine to run particularly smoothly.

The frame retained the familiar suspension designs dating from 1938, with a telescopic fork at the front and plungers at the rear. The half-width 200-mm diameter brake hubs also came from the earlier models, but were uprated.

In their first test reports, the motorcycling press praised the results achieved by BMW's engineers, particularly the smoothness of the engines and the bikes' excellent handling. When entered for the Six Day Trial in 1951, the bikes came through this first sporting challenge with flying colors.

In 1952 the leading and trailing shoe brake was replaced by a two leading-shoe pattern, and from 1953 on rubber gaiters were fitted to the telescopic forms in place of the previous metal protective sleeves. The most important innovations for the 1954 model year were full-width hub brakes and new light-alloy wheel rims instead of the previous steel ones with their two-colour paint finish. The fishtail silencers were also replaced by a less complex cigar-shaped pattern.

Whereas the R 67 was conceived with sidecar enthusiasts in mind, the R 51/3 was aimed primarily at the sporting solo rider, though it also proved its worth on more lengthy tours and with a sidecar.

The 1954 R68, below, was the 100 MPH (161 km/h) sport version of the pre-1955 BMW motorcycles. It came with 35 horsepower and more modern looking front fender.