Harley-Davidson Knucklehead

The Harley-Davidson Knucklehead is the name given to the overhead-valve V-twin engine, and the motorcycles built around it, that Harley-Davidson introduced in 1936 as the EL model, so called for the rounded shape of its rocker-arm covers, which resembled a clenched fist. It was the first Harley-Davidson production engine to use overhead valves rather than the earlier flathead layout, giving it noticeably stronger performance, and it introduced a recirculating oil system that greatly improved the reliability of earlier total-loss lubrication designs. Built through 1947 before being succeeded by the Panhead engine, the Knucklehead is widely regarded by collectors and historians as the machine that established the postwar American cruiser motorcycle look and mechanical layout.