Serpentine belt walking forward off of pulleys

[KetchiMan]

2004 Merc 5.0L MPI serial # 0W018920

So, I just had my engine pulled for a leaky oil pan and while it was out, I had the power steering pump replaced along with the, tensioner pulley, alternator pulley, idler pulley, crankshaft pulley, and circulation pump pulley. The serpentine belt is now walking forwards on the power steering and tensioner pulleys, which are right next to each other on the port side of engine. It usually just jumps a few grooves, and not all the way off, but the engine starts making some crappy noises (sounds like maybe bearings in the sea pump, idler, tensioner, or P/S pump maybe???) when the belt walks up. The crankshaft pulley is right near these other two and has no lip, but the belt doesn't seem to want to jump off of it. None of the pulleys seem visibly out of alignment.

Anybody seen this before?

 

[NHGuy]

Re: Serpentine belt walking forward off of pulleys

Take the belt off and check all the pulleys for smoothness and no play, no wobble, and parallel. Some of that stuff is hard to see with the motor running. Also look over the belt path to make sure nothing is touching the belt, look for shiny spots of worn off paint. And check that it is following the correct pattern.
Unless maybe your shop guy will do it for you. He really should have seen it before giving the boat back to you.

 

[04fxdwgi]

Re: Serpentine belt walking forward off of pulleys

It's probably out of line or a bad pulley bearing. Take the belt off and check all the pulleys for smoothness and no play, and parallelism. Also look over the belt path to make sure nothing is touching the belt, look for shiny spots of worn paint. And check that it is following the correct pattern.

Also, with the belt off, check it closely for any hooks in the belt, indicating and impending belt failure. Problem is, as NHGuy states, probably a misalligned pulley. Quite common after a bunch of stuff has been removed / replaced and put together "just slightly off". All those pulley replacements "MAY" have included a new pulley with a slightly different offset or a pulley may not have been pressed onto shaft exactly right.

 

[achris]

Re: Serpentine belt walking forward off of pulleys

Turn the belt around and see if it walks the other way... If it does, then it's a belt problem. If it's still walking the same way, then you need to eliminate the pulleys. I would put the old pulleys back on, then replace with the new ones, one at a time. You have the old pulleys, right? If not, go back to the shop who took them off and ask for them back. They are still yours...

Chris.......

 

[KetchiMan]

Re: Serpentine belt walking forward off of pulleys

Okay... got it figured, I think. Looks like the alternator was a little wiggly in it's bracket and when I put on the new tensioner (and then was able to get the belt tighter) that additional tension was enough to tilt the alternator just enough to get the belt to slip forward on the next pulley. Ran it at the dock for about 20 minutes (idled, revved, in gear, out of gear...) and no problems. Can't get out for a ride yet, but I'm keeping my fingers crossed for the test-run on Friday...