Abstract: The lower end of a crank from an internal combustion engine is pivoted on one side of the center of a small gear which in turn is mounted for rotation to one side of the center of a relatively large drive gear. A stationary gear is concentric with the drive gear and an idler gear is mounted for rotation to the drive gear and engages the small gear and the stationary gear. The drive gear engages a take-off gear to transmit power from the piston via the crank and gears. The gear ratio of the small connecting rod gear and fixed gear is such that the small gear rotates at twice the speed of the large gear. The connecting pin of the small gear is furthest from the center of the drive gear at top dead center and bottom dead center and nearest to the center at 90.degree. from top dead center and bottom dead center so that when at top dead center, the crank has the highest mechanical advantage and at 90.degree. therefrom, the lowest mechanical advantage.