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Engine Cranks but belts don't move, sometimes.....

C

casper12

New member
Hi All, Thank you in advance for your comments, suggestions and feedback!

I'll start by admitting to having VERY little engine experience but after the last repair bill maybe I should pay a bit more attention instead of cash...:(

I turn the key and the engine cranks like a champ and wants to turn over but the serpentine belt isn't spinning. Now the odd part, this only occurs SOMETIMES. Late June I had the issue while at the dock and had the mechanic visit the boat 2 days later and it fired up one turn. I then ran the boat 4+ hours the next day. Started & stopped several times and NO ISSUE. A couple of days later I went to the dock, turned the key and it wouldn't turn over. Same deal the belt wasn't spinning. Today I went down to the dock and turned the key and it fired right up.

Mechanic thought possible fuel injector issue but I don't think so as I believe I would still get crank and the serpentine belt would still spin.

Research I've done this point is suggesting either Alternator or Sea Water Pump.

My question: Has anyone encountered this issue and if so what was the ultimate issue/fix? If not, any suggestions?
 
1) Never use that mechanic again....
2) would help if you told us WHICH engine.
3) In any event... this is often a early warning that the raw water pump impeller is dying. Alternators mechanically ( assuming they don't get wet) are fairly long lived.... Raw water pump impellers are a "wear " item, and depending on lots of things have a life of anything from 20 seconds to 4-5 years.
4)..... don't use that mechanic even if he finally guesses right (on your dime).

While there is a replacement impeller available, depending on a number of factors, the "rebuild" kit is a a better idea....and once more I guessing ... since I don't know which engine you have.
 
Well....when the engine shuts down for a brief second the crank shaft will spin in the opposite direction and fold the water pump impeller vanes is the wrong direction, this is normal. The cause of the belt not moving while cranking is because it is too loose to correct the direction of the pump vanes.. You may want to tighten it slightly but not too tight because it will damage the sea water pump.

If your tensioner is at its limit and the belt is still loose, there is a larger diameter pulley available for this issue.
Last bit not least....Make sure the belt is routed correctly. It will fit if routed incorrectly and cause issues.
 
Here's another case where the word "turns over" is misused (and confusing the issue). When you hit the starter and the motor goes "RRRRR" it's turning over. If if starts up, then it's running. If it doesn't start up, however, it's still turning over, going "RRR" on the starter. Okay?

Reading the original post, be dammed if I can decipher which was happening there, but I agree the "mechanic" should take up another profession! I assume (guess) the belt is slipping like crazy--guess how long that will go on!--and something it binding, like a bad water pump, alternator freezing up, etc. A good mechanic should nail that in minutes.

Jeff
 
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