Hi Matt,
Hope all is well with you and yours!
Changing out the impellers won't be the most fun you've had aboard your boat, sorry to say. However, it is a do-able job, but you just about have to stand on your head for a while to get it done. I got down in there and wedged into place where I could get a wrench on the pump v-belt adjustment bolt, and had a tough time getting an arm free to push myself back out, ha! Your boat may have better access than mine, but my darn generator is between the motors and I wish I could wiggle my nose and have it disappear. We seldom use it because we have a great inverter setup and I don't like an air conditioner on an Express type boat.
The problem is, the sea water pump is on the bottom front section of the motor, and (as shown above) the part of the pump that opens up to give access to the impeller is facing in toward the motor block. The v-belt pully is facing forward. Although I think this job can be done by loosening the pump and rotating it around on the hoses, or one of the hoses, and changing the impeller in place, the best way to do this is to loosen the pump and just remove it from both hoses (intake hose, and outlet hose) so you can do this job on a bench.
While you're at it, you may want to replace the hoses too, especially if you damage one while getting that pump out.
Here (below) is Bill Mulvey's 427 setup in his 41 Commander, and as you can see, he has a lot better access from inside the hull than we do with our 38 Commanders. Getting to the pump on one of these motors is a lot less gymnastics.
Here is a diagram showing the sea water pump on the bottom.
Regards, good luck,
Paul
