This was the first type of British-built motorcycle engine to be produced in quantity and was manufactured by the Motor Traction Company of Kensington, London. It has four horizontal water-cooled cylinders in opposed configuration. The pistons of each pair of cylinders are in one piece and a single extended floating gudgeon pin pases transversely through their centres. The pistons move together but the power impulses, being arranged alternatively at each end of each cylinder, occur at each half revolution of the engine.
© Science Museum / Science & Society Picture Library