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Over the long winter, when cold days keep you off the water, you can still spend time with your boat and motor, taking care of small maintenance projects. Your Yamaha 15-horsepower outboard has a number of these, all important to the life of the motor. Most are required every 100 operating hours or once a year. One of these, water pump impeller replacement, is a straightforward way to get your hands a little dirty.
Items you will need
13 mm socket
Water pump replacement kit
Removing the Impeller
Set the outboard's lower unit into a vise or some other kind of brace, so that you may work on the water pump.
Loosen the 13 mm bolts holding the water pump cover in place, using a socket. Remove the bolts. Pull the water pump cover and the water pump cup from the driveshaft.
Slide the star-shaped plastic impeller off the drive shaft. As you do so, pull the small, half-moon-shaped metal tab, called the "key," from its niche in the driveshaft. Hang onto the key. Remove the pump wear plate that sets on top of the lower unit.
Installing a New Impeller
Replace the pump wear plate, found in the pump replacement kit, onto the face of the lower unit. Turn the plate, as needed, to align its mounting holes with the mounting bolt bores on top of the lower unit.
Apply a thin bead of white marine grease or plain petroleum jelly to the straight edge of the key -- there's a replacement key in the replacement kit, if needed -- and push the key into the niche in the driveshaft from which you've removed it. Push the six-bladed impeller over the driveshaft and down onto the pump wear plate, turning it to slide it past the key that will turn it as the driveshaft turns.
Place the pump cup over the impeller. Slide the pump cover back down the driveshaft, and align its mounting bolt bores with the bores on the pump wear plate.
Spread a bit of thread locking compound on the threads of the 13 mm bolts in the replacement kit. Push the bolts down through the mounting bolt holes in the pump cover and pump wear plate, and thread them into the mounting bores atop the lower unit. Tighten the new pump cover bolts to 50 inch-pounds, using a torque wrench.
- The mounting bolt bores on the top of the lower unit are offset from each other. This means that the pump wear plate and pump cover will only fit one way. It also means that you must align them properly before you insert the screws. You should insert all the screws, and thread them into the bores before you begin to tighten them.
- While the maintenance schedule tells you to inspect the water pump, doing so means removing and disassembling the pump to inspect the condition of the impeller. Since you already have the pump apart, there's no reason to face the next season with an old impeller that might shatter.
- The pump replacement kit contains: four 13 mm bolts, a driveshaft key, a water pump housing, a pump cup, one 6-bladed plastic impeller and a wear plate.
- Yamaha Outboards Repair Manual, 2.5- to 250-Horsepower, Four-Stroke, 2005-2010; Seloc Marine
- Ablestock.com/AbleStock.com/Getty Images