BuckB91XJ

OK, guys here is one for you that has me needing therapy. I have the 4.0 6 in my 91 XJ. One of the pulleys appears to be off but, I can't figure out which one or why it's happening. I perfectly align the serpantine belt and tighten it to specs. As soon as I start the motor it jumps half the width of the belt off the back of the Harmonic Balancer pulley. The belt stays on all other pulleys perfectly but, The balancer is not loose and even if it was there is no more clearance for it to be pushed back. So, I don't believe it is the problem. I did just have the power steering pump loose and the water pump and idler pulley off so I could replace a bad water pump gasket. The jeep has recently shreded 2 regular serpantine belts. One had been on the Jeep forever and the other was a brand new duralast. I put a Gatorback belt on it and this appeared to fix it until I put the Jeep back together after changing the water pump gasket. Now, no matter what I do the belt wants to slide back on the balancer pulley and stays on all other pulleys perfectly. PLEASE HELP!!!!!!!

76ANTHONY

look for a ridge in one of the pulleys, usually the idler.

BuckB91XJ

The idle pulley and water pump pulley are smooth. They were the 2 pulleys I just had off the Jeep. The fan pulley has a small ridge but it is on the rear of the pulley. I can't see that as causing the belt to want to slip off the back side of the balancer pulley.

BuckB91XJ

Well, I learned something new about my XJ and the 4.0 H.O. motor, tonight. The Harmonic Balancer and pulley is a 2 piece unit with rubber in between the balancer and the pulley. It appears that this rubber can wear out over time and the result is you balancer pulley starts walking forward on you. This causes a pully mismatch and usually a shreded belt before you notice what's happened. Somtimes a 2nd partially shreded belt and when you have a thick skull like me it takes a leaking waterpump gasket replacement and looking at things close with a flashlight after putting it back together to see where the serpantine belt is walking off the back side of the balancer pulley. Mine was only bad enough for it to have a 2 groove mismatch but that is enough for the belt to rub on the timing marks and cause the belt to shred in a short time. I can hardly wait to see what a new balancer is going to cost.....Sheesh!!!