Knucklehead

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The knucklehead was a Harley-Davidson motorcycle engine, so named because of the distinct shape of the rocker covers (valve covers). The engine is a two cylinder, two valve per cylinder, pushrod V-twin. It was the second type of engine used by Harley-Davidson, replacing the Flathead engine in 1936. The engine was manufactured until 1947 and was replaced by the Panhead engine in 1948.

As the design of Harley-Davidson engines has evolved through the years, the distinctive shape of the valve covers has allowed Harley enthusiasts to classify an engine simply by looking at the shape of the cover. A knucklehead engine has round knobs on the cover resembling knuckles that give the knucklehead its name.