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Help - Sqealing Belt

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Have been having this issue for a while now. Belt will not stop squealing like crazy. When I mount the belt, squealing will stop for a while. Then it will return, seemingly from the water pump pulley. As the belt spins, I’m nearly positive it is moving forward slowly off of the water pump pulley, as it doesn’t seem to line up perfectly after a few rotations. Not 100% sure that’s the source of the sound, but nearly positive.

 3rd belt replacement in hopes of that being the issue, mounted the most expensive one I’ve found on SummitRacing. I have tried belt conditioner (I think that stuff is worse than it is better), cleaning the pulleys, and even a bit of deodorant on the belt only silences it for a few minutes. Caused it to slip off the water pump pulley once, so I quickly turned the truck off and replaced it.


1990 MJ 4.0



Any help appreciated, thank you.

Edited by Tyler
Added engine and vehicle info.
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Absolutely check to see if the harmonic balancer isn't starting to separate and rubbing on/cutting into the timing chain cover. I personally experienced that with my Cherokee. It certainly will cause a squeal.


Belt dressing is garbage (another personal experience and opinion).  Tried that on my Comanche with a new belt that was squealing/chirping. It seemed to be eating the belt. Cleaned the idler pulley, bought another belt, and tightened the crap out of it. That solved that little issue. Couldn't sell the belt dressing at multiple garage sales for 10 cents or even give it away for free. Ended up donating it to the local Goodwill.

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Certainly check all the pulleys while the belt is off. Grab them and see if there is play. Bearings squeal too....Had that with an alternator and AC delete pulley.


Belt coming off does sound like an alignment issue. Might want to see if the bolts for the water pump pulley aren't loose.

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Definitely check over everything to make sure there is no damage and everything is straight.  


Make sure you get the belt really tight, the 4.0 belt needs to be tighter than other vehicles.  Should only be able to get a max of 1/4 twist in the belt with your fingers.  


The belt on my XJ squealed for about a month after I took it off to do some work.  Belt dressing always seemed to make it worse but after 10 mins of running it got better.  Eventually it finally quit for good.

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