How to Change the Water Pump Impeller in a Mercury Boat Motor
- 1). Loosen the four nuts on the lower gear box of the Mercury boat motor that fastens the gear box to the motor housing with a socket wrench. Remove the nuts by hand and pull the gear box away from the motor housing.
- 2). Locate the water pump housing on the top of the gear box and remove the four bolts on the top of the housing with a socket wrench. Take the water pump housing off the motor shaft and turn the pump housing over to locate the impeller inside the housing.
- 3). Remove the plastic impeller from the housing and take the rubber gasket off the top of the gear box. Lift the keyway out of the slot on the gear box and remove the metal plate from the surface of the gear box.
- 4). Remove any gasket material from the top of the gear box with a putty knife and place a thin coat of marine grease where the water pump housing sits as well as around the motor shaft. Place the metal plate on the top of the gear box with the rounded side facing up and put the rubber gasket over the metal plate.
- 5). Set the keyway in the slot on the top of the gear box and put a thin layer of marine grease around the inside of the water pump housing. Slide the new impeller upside down into the water pump housing and attach the pump housing to the top of the gear box with bolts, lining up the keyway with the slot in the new impeller.
- 6). Secure the gear box of the Mercury boat motor to the motor housing with the nuts.