2000 mercruiser 5.7 bravo engine with raw water pump issue

[thesunscreen]

Hey thanks for looking. I'm swining around my mooring this afternoon and ran into yet another problem. I have a 26' aft cabin welcraft powered by a fresh water cooled 5.7 mercruiser. If I run the boat everything is fine but if it sits for a while the pump locks up and the belt squeals.

Now this is the important part, if I drop the serpentine belt I can spin the pump in reverse with relative ease. This has happened several times and what seems to be happening is the vanes in the impeller are flipping over. If I really struggle I can turn the pump in the correct direction and it will work again. The pump was rebuilt by the previous owner and I took it apart when it did this the first time and everything looks fine. I reasembled the pump the first time and it worked for a while on the trailer. Then it happened three more times each time after sitting for a while. It almost seems like the impeller is in backwards but everything I read on it doesn't seem to have a right way and a wrong way.

[Don S]

Remove the pump, disassemble and inspect. Could be a number of things, but they will be obvious on visual inspection.

[thesunscreen]

Did that, even mentioned it in my first post. Nothing is obvious.

[Don S]

If the pump is locking up, the bearings are shot, and it should be obvious when you remove the impeller. The pulley should turn with no roughness and absolutely no side to side movement.

[thesunscreen]

Nope, they are fine. Pulled the pump apart and they spun free, no grinding binding or otherwise.
Is there a possibility that the impeller is in backwards or upside down? I know there is a keyway and it slides down one way, but flipped over it should slide down the same way. If the motor rocks back occasionally when shutting down on a compression stroke its enough to flip the vanes over causing this problem where it can't flip them back over when running. Are they made more rigid one way than the other to prevent this from happening?

[TilliamWe]

Your belt isn't tight enough. When you are shutting the engine down, it's "rocking back" a little, and the vanes flop over. Then when you start it, the belt isn't tight enough to turn the pulley to flip the vanes back over. I did that once in my Bravo after an impeller change. Took it off, re-assembled it, and made sure the belt was clean and tight, and it never did it again.

[thesunscreen]

That doesn't make sense at all.
1st. My belt is tight enough to play the banjo. about 1/4" of deflection in the belt.
2nd The crank is rocking back pulling the other accesories backwards slightly. Having the belt too loose would mean possible slippage. I can't see how belt tension would stop the motor turning backwards thus turning the raw water pump backwards. The only thing tightening the belt might acomplish is allowing the torque of the engine to snap the vanes in the right direction again. Maybe thats what happened with yours.

However my belt is as tight as is reasonable and recommended.

[Bt Doctur]

If I run the boat everything is fine but if it sits for a while the pump locks up and the belt squeals.

Is there any chance it`s diseling when you shut it down? thats the only way to reverse the vane and find it reversed on the next start up.

[TilliamWe]

Sunscreen it makes perfect sense. If your engine is rocking back slightly, it's flopping the vanes over. Then if the belt isn't tight enough or worn, it slips due to the added force it takes to flop the vanes back over. However, if you say it's tight enough, it must be.
But first, your engine shouldn't be rocking back that much. Then if it is, you either have a belt problem or something inside the pump housing is preventing or causing the vanes from flipping back over.