Abstract: This invention is designed to increase the net engine efficiency of four body linkage mechanisms used to generate power or do useful work. This is accomplished by decreasing the piston velocity in the first half of the power stroke of a typical engine cycle. The piston velocity is altered by the addition of three components at the crankarm pin location on the crankshaft. The new components convert a normal engine from a four body to a five body linkage mechanism. One component is an eccentric pin and the other two are an internal ring and pinion gear assembly that indexes and rotates the eccentric pin in a fixed relationship with the crankshaft rotation. The pinion gear and eccentric pin are integral and rotate together as a single part in a direction opposite to the crankshaft rotation. The outer eccentric diameter moves up as the crankarm moves down during the first part of the power stroke.