This listing is for a Cloyes timing gear set compatible replacement for Chevrolet 2.5L (153ci) and 3.0L (181ci) mercruiser marine engines used by Mercury Marine, OMC, and various other marine companies. P/N 2528S. These engines are also characterized by their horsepower ratings. The 2.5L is a 120HP, and the 3.0L is a 140HP. This gear set has a heavy duty ALUMINUM cam gear for your marine engine needs. This set features a 54-tooth cam gear and a 27-tooth crank gear.