Difference between revisions of "Harley-Davidson Evolution"

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 iron (reducing overall vehicle weight) and a superior thermal conductor to 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.<ref>[http://www.accubiltonline.com/ Accubilt Online<!-- Bot generated title -->]</ref> In water-cooled vehicles the oil and water will often mix and contribute to lubrication failure and engine destruction. The blocky rocker boxes, 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 [[Harley-Davidson Sportster|Sportster]] incarnations of the Evolution are significantly different.