Flathead: 1909-1936

The Flathead was named because of the tell-tail flat vented tops that are recognizable at the top of each cylinder head. This is the famous motor that propelled the Harley-Davidson to victory after victory in the motorcycle races of the twenties.

Knucklehead: 1936-1947

Just at the start of WW2, Harley-Davidson introduced an overhead-valve V-twin with knuckly looking valve covers when viewed from above. The new motor, affectionately known as the "Knucklehead", performed well both for HD and for America in the difficult years to come.

Panhead: 1948-1965

With improvements to the engine design, like hydraulic valve lifters that supplied oil to the rocker arms, the Panhead hit the market in 1948. Named for the pan-like valve covers replacing the knuckle covers.

Shovelhead: 1966-1983

By 1966 the Panhead underwent still more improvements. The most noticeable being the distinctive enclosed cylinder head in a sleek, slightly curved top. At a glance this looks unmistakably like a shovel with the pushrods tubes resembling the handle of a shovel, and the shovel itself.

Evolution: 1983-1999

In 1984 on the heels of the employee buyout of AMF, Harley went public and introduced its now famous redesign of the V-twin. This radical new design utilized styled square blocks to house the valve train. This motor, revered as the Evolution engine is known amongst Harley enthusiasts as "the Blockhead".

Twin Cam 88: 1999-Present

With numerous American motorcycle manufacturers trying to surface and resurface, Harley-Davidson introduces its most revolutionary engine yet. The Twin Cam 88 gets its name from its two cams versus the single cam in all its ancestors. This motor also goes by the nickname "Fathead" for just exactly that, bigger heads. With this new engine design Harley-Davison puts one more notch in its insurance for success