I replaced the motor in a 2002 Altima (2.5l) because it had a blown headgasket. Everything went back together fine, and it runs well, but when the car is running, the serpentine belt is only halfway on the tensioner. When I got a buddy to loosen the tensioner and I pushed it back into place, it wobbled halfway off as soon as the car was started.

The alternator, power steering pump, and A/C compressor were the same that were on the old motor. The alternator bracket is the one that came on the new (used) motor, as well as the water pump and tensioner.

The crank does not have play in it, neither does the tensioner pulley, alternator pulley, or the power steering pump pulley. But SOMETHING has to be getting it off track! Any ideas?

We're thinking of putting the old water pump and old tensioner on it to see if that corrects the problem. We're not sure how the used car place pulled this motor, and they could have used one of these pulleys as a hook-up point to move the motor around.

Did you find out? It sounds like the pulley prior to the belt tensioner is off center, or the belt tensioner is. If you look at them carfully you should be able to tell which one doesn't match the straight line of the rest of the pulleys.

I’ve had this issue before and found that the bushing that’s on the alternator was missing or the tensioner itself was just worn out and another occasion where the crank damper pully was at fault. The rubber gets old and throws everything off. Seen one occasion where the whole harmonic ballancer had seperated. Never could find the other half. Make sure the harmonic ballancer bolt is tight as well.