Tucson, Arizona, & Madison, Wisconsin
BMW Used to Manufacture Shaft-Drive Thumpers! An R27 engine is shown below.
From the 250cc OHV R39, above left, of 1925 through the 1954 R25/3, above right, to the R27, BMW made shaft-driven thumpers ranging from 200cc (1931 R2) to 400cc (1932 R4) in almost as many permutations as its more famous opposed boxer twins. Most of the models, however, had bores and strokes both of 68mm, producing 247cc. Frame and suspension changes paralleled those of the twins
The last single-cylinder shaft-drive BMW motorcycle model made was the relatively powerful and elegant R27, a 250cc OHV vertical single with the only rubber-mounted thumper engine BMW ever produced. The engine pumped out 18 horsepower, the highest ever for a shaft-drive BMW single. BMW manufactured 15,364 R27s over the production years of 1960 through 1966 (some of the 1966 R27s were sold as 1967 models).
The illustration above on the right shows the cover of a 1960s BMW R27 sales brochure.
Compared to other manufacturers' thumpers, what were some of its unusual features?
What other BMW shaft-driven singles were manufactured after World War II?In all, BMW produced six shaft-drive thumpers after the war, all with similar 250cc OHV engines. The first, in 1948, was largely a copy of the pre-war R23 and was designated the R24 (engine numbers 200 009 - 212 007). It was unique in that it had no rear suspensionthe only postwar BMW so unequipped (see photo below). Thereafter, from 1950 to 1956, came bikes with rear plungers and front telescopics, all having exposed shaft drives and bell-bottom front fender skirts. These were the R25 (engine numbers 220 001 - 243 400), the R25/2 (engine numbers 245 001 - 283 650), and the R25/3 (engine numbers 284 001 - 331 705).
Above: a 1949 BMW R24.
In 1956 BMW introduced a completely revamped thumper, the R26 (engine numbers 340 001 - 370 236), with improvements paralleling those introduced at the same time in the boxer twins. The R26 came with an enclosed drive shaft, rear swingarm, and front Earles forks. A new headlight nacelle came with a sliding black plastic over the ignition key, and the bell-bottom front fender was dropped along with the mechanics' hand shifter. The engine of the R26 was bolted directly to the frame, and the engine wailed away with 15 horsepower.
Based largely on the R26, the R27 added rubber mounts for the engine, which markedly reduced the R26's vigorous rider massages, and boosted horsepower by three to 18.
What are the specifications of the R27?Here are the main ones:
Curb weight with fuel, oils, tools 356 pounds (162 kg.)
GVWR 716 pounds (325 kg.)
Fuel tank capacity 4.0 US gallons (15 liters)
Engine oil capacity 2.6 US pints (1.25 liters)
Engine oil type SAE 40 (86°+), SAE 30 (32°-86°), SAE 10W30 (below 32°)
Transmission oil capacity 1.3 US pints (650cc)
Rear drive unit oil capacity 125cc
Transmission and rear-drive oil type SAE 90 gear oil or SAE 40 engine oil
(depending on the year of manufacture)
Wheelbase 54.3 inches
Overall length solo 82½ inches (2090 mm)
Handlebar width solo 25.6 inches (660 mm)
Overall height solo 38.4 inches (975 mm)
Saddle height 30.2 inches (770 mm)
Ground clearance 4½ inches (115 mm)
Maximum brake horsepower 18 HP at 7,400 RPM
Bore and stroke 68mm × 68mm
Cylinder capacity 247cc (15 cubic inches)
Spark plug Bosch W240T1, Beru 240/14, or Champion L85
Intake valve clearance, cold engine .006 inches (0.15 mm)
Exhaust valve clearance, cold engine .008 inches (0.20 mm)
Compression ratio 8.2:1
Top speed 80 MPH (130 km/h) depending on conditions and wind
Predicted mileage 60 miles per US gallon (DIN 70030)
Tires 3.25 x 18, front and rear
Battery 6 volts, 9 Ah.
Headlamp 6 volts, 35/35 watts
Below is a of a 1966 BMW R27 restored by the noted BMW restorationists, Chris and Barbara Betjemann, of the Barrington Motor Works, in New Hampshire. They are currently preparing an R27 restoration and service BMW R26-27 Restoration and Sevice Manual to join their BMW slash-2 and slash-3 twins restoration and service manuals. Note the rare and beautiful parade tank. Photos below by Barbara Betjemann.
Below are pages from the 1960 BMW R27 brochure
Here is Allan's incredible R27 Restoration Story!