Harley-Davidson Evolution Engine

Harley-Davidson Evolution Engine

The Evolution engine (popularly known as Evo) is an air-cooled, 45-degree, V-twin engine manufactured from 1984 to 2000 by Harley-Davidson for the company's motorcycles. It was made in the 1,340 cc (82 cu in) displacement for Harley Davidson Big V-twins bikes, replacing the Shovelhead engine, giving way to most of the product line utilizing the new TC88 (Twin Cam 88 cu in), until 2000 when the last EVO was placed in a production factory custom (FXR4). In 2001, it was completely replaced by the Harley-Davidson Twin Cam 88. It was made in the 1,100 cc (67 cu in) displacement and is still made in the 883 cc (53.9 cu in) and 1,200 cc (73 cu in) (replacing the 1,100 in 1988) displacements since 1986 for the Harley-Davidson Sportster, where it replaced the ironhead Sportster engine.

Most analysts consider the Evolution to be the engine that saved the reorganized Harley-Davidson company from certain bankruptcy. Harley-Davidson's official name for the engine was likely related to the company's reformed image following the Harley Davidson leadership_regained/1981 employee-led buyback from AMF.

Though a major design advance for Harley-Davidson in many ways, the Evolution is most distinct from earlier Harley-Davidson engine designs by virtue of its reliability, oil tightness, and ability to be run hard under all kinds of circumstances for tens of thousands of miles farther than any of its predecessors. Both the heads and cylinders of the Evolution engine are made from aluminum, which is both lighter than cast iron, reducing overall vehicle weight and a superior thermal conductor to cast iron - improving air cooling efficiency. A problem is avoided thereby which occurs when the heads and cylinders are of different materials. They expand and contract at different rates which induces a relative motion; this motion ruins the gasket seal and necessitates replacement. The blocky rocker boxes (thus becoming nicknamed "block head"), aluminum heads and cylinders (also referred to as "jugs") are the only part of the Evolution engine that can be said to be essential; the Big Twin and Sportster incarnations of the Evolution are significantly different.