Abstract: A variable stroke mechanism provides a means for varying the stroke and leverage of a linkage between reciprocating power source and crankshaft. The mechanism includes a lever connected at one end to the reciprocating power source and at the other end to the crankshaft with a variable fulcrum point between the two ends. The lever forms a longitudinally extending slot for containing a fulcrum member, the other surfaces of which, while generally cylindrical, secures a series of parallel and equiangularly displaced cylindrical roller bearings. The top of the slot formed within the lever is a flat bearing surface and the opposing bottom surface contains a series of semicircular channels forming a gear train sized and located to successively engage the roller bearings on the fulcrum member and said bearings serving as gear teeth such that rotation of the fulcrum member changes the position of the fulcrum point relative to the lever.