The Sportster is a line of motorcycles produced continuously since 1957 by the Harley-Davidson Motor Company. Sportster models are designated in Harley-Davidson's product code by beginning with "XL". In 1952, the predecessors to the Sportster, the Model K Sport and Sport Solo motorcycles, were introduced. These models K, KK, KH, and KHK of 1952 to 1956 had a flat head engine, whereas the later XL Sportster models use an overhead valve engine. The first Sportster in 1957 featured many of the same details of the KH including the frame, fenders, large gas tank and front suspension.
Sportster motorcycles are powered by a four-stroke, 45 degree V-twin engine in which both connecting rods, of the "fork and blade" or "knife & fork" design, share a common crank pin. The original Sportster engine was the Ironhead engine, which was replaced with the Evolution engine in 1986.
1972 "Ironhead" 1,000 cc overhead-valve engine replaces 900 cc.