Sunbeam motorcycle engine, 1948.
© Science Museum / Science & Society Picture Library
This was the engine for the Sunbeam S7 motorcycle designed by Erling Poppe and first produced in 1947. It has two cylinders in-line and the cylinder block and crankcase in one piece. The casing of the four-speed gearbox is bolted to the engine crankcase. There is a single-plate clutch, shaft drive to the rear axle, overhead camshaft and coil ignition.