The knucklehead is a retronym used by enthusiasts to refer to a Harley-Davidson motorcycle engine, so named because of the distinct shape of the rocker boxes. The engine is a two cylinder, 45 degree, pushrod actuated overhead valve V-twin engine with two valves per cylinder.
It was the third basic type of V-Twin engine used by Harley-Davidson, replacing the Flathead-engined VL model in 1936 as HD’s top-of-the-line model. The engine was manufactured until 1947 and was replaced by the Panhead engine in 1948. The Knucklehead-engined models were originally referred to as “OHVs” by enthusiasts of the time and in Harley’s official literature; the nickname arose from the California chopper culture of the late 1960s.
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. The knucklehead engine valve covers have contours resembling knuckles on a person’s fist that give the knucklehead its name.
Harley-Davidson, Inc. (H-D), or Harley, is an American motorcycle manufacturer, founded in Milwaukee, Wisconsin in 1903.
As one of two major American motorcycle manufacturers to survive the Great Depression (along with Indian), the company has survived numerous ownership arrangements, subsidiary arrangements (e.g., Aermacchi 1974-1978 and Buell 1987-2009), periods of poor economic health and product quality, as well as intense global competition — to become the world’s fifth largest motorcycle manufacturer and an iconic brand widely known for its loyal following — with owner clubs and events worldwide as well as a company sponsored brand-focused museum.
Noted for a style of customization that gave rise to the chopper motorcycle style, Harley-Davidson traditionally marketed heavyweight, air-cooled cruiser motorcycles with engine displacements greater than 700 cc — and has broadened its offerings to include its more contemporary VRSC (2001) and middle-weight Street (2014) platforms.
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