How to Replace the Water Pump on a Yamaha 115 HP Outboard

The water pump on a 115-horsepower Yamaha outboard motor is simple to replace and inexpensive to do so. The rubber impeller blades deteriorate due to the sediment in the water and especially if it is used in salt water. The pump should be replaced as a preventative maintenance procedure each season. If it fails while on the water, the engine will quickly overheat, resulting in costly engine damage. Peace of mind is worth much more than the pump, given its low cost.

Instructions

1

Place the Morse engine control in neutral. Tip the engine slightly so it isnt vertical. Remove all but one nut securing the lower unit to the engine case using a socket. Leave one of the nuts loose to keep the lower unit from falling when all the nuts and bolts are removed.

2

Remove the Allen head screw located in the anode plate under the cavitation plate just above the prop. Remove the plate and the bolt located inside above the plate using a socket.

3

Hold the lower unit securely because it is slightly heavy. Remove the last nut securing the lower unit. Lower the unit slowly just enough to disconnect the plastic speedometer pilot tube at the hard plastic connector now exposed. Lower the unit the rest of the way and move it to a spot that it can be held upright while being worked on.

4

Remove the four bolts in the black water pump housing with the driveshaft running up through it. Lift the water pump housing off over the driveshaft. Lift the black rubber impeller up and off the driveshaft. The impeller is prevented from spinning by a Woodruff key, a semicircular shaped piece found in the driveshaft.

5

Inspect the key for rusting or damage and replace it with the new one from the kit, if necessary. Inspect the base plate under the impeller and replace it if it is grooved excessively. Install the new impeller over the driveshaft and down over the key.

6

Place some grease on the impeller blades to protect them when the housing is installed. Install the new water pump housing with a new rubber gasket over the driveshaft and seat it over the impeller. Install the four bolts. Lift the lower unit and carefully insert the driveshaft into the output shaft of the engine.

7

Lift the unit enough to reconnect the speedometer hose. Slide the unit the rest of the way up. Install the side nuts on the upper unit studs. Install the bolt above the anode and install the anode with its Allen bolt.