- Flathead engines - Manufactured between 1929 and 1974. Flatheads did not have overhead valves. Instead, the valves ran alongside the engine and opened upwards into a chamber beside the combustion chamber. The advantage of a flathead was simplicity -- no pushrods or rocker arms, and the head was a simple casting with a hole in it for the spark plug. A typical flathead engine had a displacement of 45 cubic inches (742 cc) and produced about 22 horsepower.
Basic design of a flathead engine.