The Harley-Davidson EL model was the first motorcycle powered by the overhead-valve Knucklehead engine.
Harley-Davidson introduced the 61-cubic-inch EL in 1936. Its new overhead-valve V-twin became known as the Knucklehead because the rocker-box covers resembled a row of knuckles. The engine replaced the company’s earlier flathead and F-head approaches in the high-performance Big Twin sector.
The EL’s 61-cubic-inch engine represented a major advance in breathing and power. Its overhead-valve layout allowed the engine to operate more efficiently than Harley-Davidson’s side-valve Big Twins, helping establish the performance direction that later led to the Panhead, Shovelhead, Evolution, Twin Cam, and Milwaukee-Eight families.
The EL designation is sometimes confused with FL, which identified the larger 74-cubic-inch Knucklehead introduced in the same general era. Both were Knucklehead models, but the EL was the first production application of the engine.