Built for Speed: BMW 255 Kompressor Engine

Pertinent details about the 1939 BMW 255 Kompressor engine.

Kompressor Carburetor

A single Amal carburetor feeds the supercharger on the front of the engine.

Photo by Neale Bayly

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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.