The maintenance schedule for your Mercruiser Alpha One sterndrive is specific. You're supposed to inspect your water pump every 100 hours of operation or annually, whichever milestone occurs first. The not-so-good news is that if the impeller has missing or damaged blades, you have to replace it. The good news is that, even though your boat's an inboard-outboard, the drive unit attached to the transom assembly is the same as an outboard's lower unit.

Removing the Impeller
1. Tilt the sterndrive up to a 45-degree angle and position an oil drain receptacle below the drive oil fill-and-drain hole. Remove the drive oil fill-and-drain screw and its sealing washer, using a small, flat-blade screwdriver, and set them aside. Remove the vent screw and its washer, and drain the oil from the drive unit. Use a piece of tape to mark the position of the trim tab on the bottom.

2. Remove the trim tab; the nuts, bolts and washers from the port and starboard sides of the unit; and the nut from the front of the unit, using a 1/2-inch socket. Remove the screw found in the well from which you removed the trim tab using a large flat-blade screwdriver. Pull straight down on the drive unit to remove it from the transom assembly.

3. Remove the seal from the face of the water pump body. Pull up on the water-tube coupling to remove it and remove the screws from the water pump body. Slide the water pump body up the driveshaft. Slide the impeller from the driveshaft and pull the impeller key away from the driveshaft. Slide the pump faceplate up and off the driveshaft. Inspect the interior of the pump body for scoring and the pump faceplate for roughness and replace, as necessary. Use a small putty knife to scrape any gasket material from the top of the drive unit.

More: Mercruiser alpha 1 water pump kit
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