The Yamaha outboard motor propeller provides the thrust needed to push a boat through the water. Propellers come in two-, three- or four-blade designs, with diameters of varying sizes. Propellers have various pitch angles that determine the amount of thrust applied for hole shot acceleration, planing and wide-open throttle. Propellers endure more punishment that just about any other outboard motor component; for this reason, they must be inspected regularly and replaced when they become damaged. Damage occurs as a result of object strikes, metal fatigue and prolonged wear. Any boat owner can replace a Yamaha propeller by using basic tools.
Place your boat on a trailer and move it to a convenient work location. Chock the wheels or keep the trailer hitched to the tow vehicle. Use a socket and wrench to remove the negative battery cable, if your outboard has an auxiliary battery. Remove the ignition key. Place the outboard motor in the full tilt-down position, with the transmission shift lever in neutral. Use side cutters to snip away any seaweed or fishing line from around the propeller shaft.
Use side cutters to cut the end of the cottar pin that goes through the castellated shaft nut, and pull it out. Wedge a small wood block between the propeller blades and the lower unit motor housing, to stabilise the propeller. Spray the shaft nut with penetrating oil and let soak. Place a socket on the propeller shaft nut and turn it counterclockwise with a wrench. Unscrew the nut and take the spacer off. Pull the propeller straight off the shaft.
Use a plastic hammer to tap the back of the propeller shaft flange, if the prop appears stuck. Pull the propeller off. Determine if the propeller has an interior hub sleeve. If so, remove it and clean it with a rag. Place the interior hub sleeve inside the new propeller, making sure it fits properly onto the notches. Set the propeller aside. Pull the thrust washer off the propeller shaft and inspect its taper for even wear. Clean the thrust washer with a rag.
Wipe the propeller shaft off with a rag and apply some marine grease to the shaft and splines. Place the thrust washer back over the shaft. Align the new propeller on the prop shaft. Line the key way up with the key in the inner hub. Shove the propeller toward the transom until it sits flush. Insert the spacer on the prop shaft, then the castellated nut. Tighten the castellated nut with a socket, but only snug tight.
Place the wood block in-between the propeller blades and the lower unit motor housing. Refer to your owner's manual for the proper torque in foot-pounds for the castellated nut (it should be around 40 foot-pounds). Torque the nut to specifications. However, twist the torque wrench slightly in or out to align the castellated nut notch with the shaft hole. Place a new cottar pin in the nut and flare the ends with the side cutters. Reconnect the negative battery cable with a socket.
Although not necessary in every case, you can replace the old shaft key with a new one. Check the thrust washer for unusual wear. You can replace the thrust washer while you change out the propeller. If the propeller remains fixed to the shaft, you will need to use a special gear puller to remove it. You can rent gear pullers from automotive or marine supply stores.