Re: 4.0hp water pump impeller replacement
Even if you were to install the new impeller with the vanes pointing in the opposite direction, they will right themselves to the correct orientation once the motor starts.
That being said, good shop practice dictates that you may as well have them pointing the right way in the first place. All modern outboards (with likely the rare exception but none I know of) rotate clockwise as viewed from the flywheel end.
So, you'll want to rotate the driveshaft CW as you're looking down as the lower unit. Note to be sure and rotate the impeller and driveshaft together, with the slot in the impeller aligned with the impeller drive key. As you turn the impeller, force it into the pump housing until it engages the key.
A dab of grease on the flat of the driveshaft will help hold the key in place until the impeller is fully seated. Making a mark on the driveshaft, up-side of the pump, indicating where the key is, will help you align things properly. It's hard to see where that key is once the impeller starts going into the pump.
One word of caution, it's real easy for the key to slide away as you're installing the impeller.
After you have the impeller fully seated, gently hold onto it and move the driveshaft to and fro. You'll know right away if the key engaged the impeller, as you'll feel a slight amount of free play before the impeller starts moving with the driveshaft.
If the key didn't engage, pull the impeller out, reposition the key, and give it another shot. Repeat until Victory! You'll find that with practice you'll get pretty good at this but it's a bit tricky the first few times.
HTH & G'luck........ed
