Built for Speed: BMW 255 Kompressor Engine

Pertinent details about the 1939 BMW 255 Kompressor engine.

| September/October 2012

  • Kompressor Carburetor
    A single Amal carburetor feeds the supercharger on the front of the engine.
    Photo by Neale Bayly

  • Kompressor Carburetor

The 1939 BMW 255 Kompressor was a machine ahead of its time. Here, according to John Surtees, are some of the more pertinent details in regards to the Kompressor engine.

• The flat twin transverse engine features twin overhead camshafts for each cylinder, with short rockers operating two valves per cylinder. A Zoller supercharger is mounted on the front of the engine, fed by a 27mm German Amal carburetor. From the supercharger, two pipes run under the engine into the inlet ports at the rear of the cylinders. Long, slow-taper megaphone-type exhausts are featured.

• The engine features beautiful castings, some of which are in magnesium. The dual-outlet Bosch magneto mounted on top of the engine is driven by gear from the front, firing two 14mm spark plugs. In 1939, the engine ran on a 50/50 benzole and gasoline mixture, with 2 percent castor oil to provide lubrication for the supercharger. The engine drives the 4-speed gearbox via a single-plate clutch.

Read more about what makes the BMW 255 Kompressor such an important bike in The BMW RS 255 Kompressor: Making History Going Fast.

November December Vintage Motorcycle Events

Blue Moon Cycle Euro Bike Swap Meet and Vintage Ride

Make plans for the 28th Annual Blue Moon Cycle Euro Bike Swap Meet on Saturday, Oct. 27, followed by the Blue Moon Cycle Vintage Ride on Sunday, Oct. 28!