US Patent 6893305 Shift mechanism for marine propulsion unit

A marine propulsion unit has a driveshaft and propulsion shaft driven by the driveshaft and driving a propeller. The driveshaft carries a pinion. The propulsion shaft carries forward and reverse gears. The pinion meshes with the forward and reverse gears. The pinion drives the forward and reverse gears in opposite directions relative to each other. A sleeve is rotatable with the propulsion shaft. The sleeve is slidably disposed between the forward and reverse gears on the propulsion shaft. The forward and reverse gears have teeth on a surface thereof that opposes the sleeve. The sleeve has recesses on each surface thereof that opposes the forward or reverse gear. Each tooth can enter a corresponding recess. The tooth has a length substantially the same as a length of the recess in a circumferential direction.