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 are not always considered to be Sportsters, but are definitely the precursors and inspiration for the line. Sportster motorcycles are powered by 45 degree V-twin engines in which both connecting rods, of the "fork and blade" or "knife & fork" design, share a common crank pin. The Sportster, the 45" R, D, G & W Models 1929-–3 side-valve motors, and the 'Big Twin' side-valve motors, which were: the flathead 74 cubic-inch (1213 cc) Models V , VL etc.

(1930–1936), Models U and UL (1937–1948), and the 80 cubic-inch (1311 cc) Models VH and VLH (1935–1936), Models UH and ULH (1937–1941) have four separate cams, sporting one lobe per cam. The OHV 'Big Twins' used a single cam with four lobes until 1999 when the 'Twin Cam' appeared, with two cams and two lobes per cam. Incidentally, the cam followers used in the Sportsters, K models, big twin side valve models, and the side-valve W Model series were a slightly shorter version of the followers used in the larger motors, but with the same 0.731 inch diameter body and 0.855 inch diameter roller follower since 1929.

The company used similar cam followers for decades with minor changes, from the 1929 to the Eighties, probably the longest run for any engine part anywhere, in all Harley motors made those years one of these is called out.

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