Above: Top view of an R51/3. The lid on top of the gas tank opens to reveal a complete tool kit.
Note that the left cylinder is mounted forward of the right cylinder so the connecting rods can pass each other.

1951-1954 BMW R51/3
including references to the R51/2 and R68

by Jeff Dean

Last Updated

Above: A 1954 R51/3, restored and being ridden by Tim Stafford, of San Diego, California. Note the full-width brakes, which are characteristic of the 1954 model.

1952 BMW R51/3

Above is a 500cc BMW 1952 BMW R51/3 (60 years old!). It was beautifully restored in 2007 by Craig "Vech" Vechorik, of Bench Mark Works USA, Sturgis, Mississippi. Note the plunger rear suspension, exposed and chromed drive shaft, telescopic forks, and half-width brake drums.


Above, left: Note the exposed driveshaft, plunger rear suspension, painted wheel rims, and mechanic's hand shift above. Above, right: note the fishtail muffler, grab rail, and small tail-light.

The photo below shows a 1954 R51/3 restored beautifully by Tim Stafford in San Diego in 2008 and 2009. The saguaro in the photo reveals it was taken in southern Arizona.

The image below shows the original R51/3 in the BMW brochure of 1952. Note the metal sliders on the front forks used instead of rubber gaiters for the first couple of production years and the fish-tail muffler.

The factory photo below shows the 1954 version of the R51/3. Note the full-width brakes, rubber gaiters, and the seamless cigar-shaped mufflers.

In 1952, the R51/3 came with half-width brakes and painted steel wheels (photo below, left). In 1954, it came with full-width brakes and aluminum wheels (photo above and below, right).

The photographs below are of a 1954 R51/3 (note the full-width brakes) in the earliest stages of restoration. The engine (center) and rear drive housing (right) have been restored.


The photos below shows the 1954 R51/3 in March 2009, the restoration by Tim Stafford having been completed. I always liked the front view of an old BMW twin because of the protruding cylinders.

The photographs below shows the original Veigel speedmeter in kilometers found on an R51/3 sold originally in Europe. It had convex glass, unlike VDO speedometers.


The photograph below, left, shows the BMW roundel on the gas tank of an R51/3. Note the serif typeface. The type face on the later Slash-2 models was sans serif.

The photograph below, right, shows a 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.

Not all R51/3 riders in 1951 were men.


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 page below was published in the brochure, BMW Motorräder 1951, with German text. Note that the air cleaner housing is an earlier version than the one shown in the 1952 brochure image above. Here, in italics, is a “loose” translation of the text:

BMW R51/3

Touring-Sport 500cc — 24HP

Among experts, this two-cylinder motorcycle is called “a work of art in metal.”

As its looks suggest, the sporting features of its reliable high speed engine are technically perfected, including a gear driven cam shaft and a magneto ignition. The two-piece valve covers [of the R51/2] have been replaced by single, ribbed covers, which conform to the smooth and appealing shapes of the engine’s unit cases. Sporting riders will like the 135 km/h (84 MPH) top speed, but find they can also go down to 20 km/h (13 MPH) in fourth gear. The well spaced gears in the four speed transmission, with a drive shaft and foot-operated shift lever, can be operated easily and safely. A green light on the headlight nacelle indicates neutral.

The chassis, with suspensions at both wheels, has been tried and proven on all the streets of world. The comfortable and adjustable fully sprung saddle, together with the fully enclosed telescopic front forks and rear plunger suspensions, produce excellent riding comfort and road holding, which is confirmed by numerous BMW racing wins. The wheels, with 3.50x19 tires, are interchangeable. The front wheel stand and the folding rear stand enable trouble free wheel changes. Enclosed and powerful internal shoe 200 mm (7.9 inch) diameter brakes convey a feeling of total driving security in every situation.

Incomparable in acceleration, superb road holding, and long life on the highway.


Below is a two-page spread on the R51/3 from the December 1952 issue of Cycle magazine. Click here or on the image below to see a large format version of this article. (If your mouse pointer is a small "+" inside a circle when you view it, click anywhere on the photo to enlarge it.)

The 1955 R67/3, below, almost identical visually to the 1954 R51/3, was the low-compression 600cc version of the R51/3. It was also the last of the plunger suspension BMW motorcycles, overlapping for two years the introduction of the slash-2 models.

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.



R51/3 — R67-R67/3 — R68
Rear Drive Ratios
R51/3 Solo35 / 9   (1:3.89)
R51/3 Sidecar32 / 7   (1:4.75
R67 — R67/3 Solo32 / 9   (1:3.56)
R67 — R67/3 Sidecar 35 / 8   (1:4.38)
R68 Solo35 / 9   (1:3.89)
R68 Sidecar32 / 7   (1:475)

What about maintenance-free 6-volt batteries for the R51/3, R67/3, or R68? Bench Mark Works now has the solution. Its part number is 61 21 8 042 025S — for the Noris AGM original style hard case battery with square lid. Dimensions are 6 716 x 358 x 3316 inches, or 92x82x166 millimeters.

 

The new 500-page slash-3 restoration and service manual, above right, by Christopher and Barbara Betjemann of Barrington Motor Works, is the finest and most complete book ever published on servicing and restoring these motorcycles.

You can order it here — Barrington Motor Works Manual Order Page

It may be an expensive book, but do not touch your slash-3 unless you have it by your side!


Click here to read English R51/3 specifications from BMW A.G., Munich, Germany.

Click here to see the technical data from from the February 1952
English-language owner's manual for the R51/3 and R67/2.

Click here to read Wikipedia's R51/3 article.

Harley's interesting 1942 XA boxer with shaft drive.

Hier klicken, um den R51/3 Wikipedia Artikel auf Deutsch zu lesen.

Click here for a speedometer ratio test form