1936 was the first year for the Model E, which was nicknamed as the "knucklehead" due to the knuckle shape of its engine valve covers. The Model E was a slowly gained popularity, but it was the distance record set by Fred Ham that put the knucklehead Model E into the history books.
1937 Harley-Davidson Model E Knucklehead
1937 Harley-Davidson EL 1000 Knucklehead
1940 Harley-Davidson EL 1000
1947 Harley-Davidson EL 1000
The last of the 'Knuckleheads' was produced by Harley-Davidson in 1947. The new versions of Harley's OHV engine were introduced in 1948, featuring chrome-plated valve covers that resembled upside-down cake pans. This was the beginning of Harley-Davidson's "Panhead" era.
