Can't find the cause, belt squealing and poor charging

[SCW]

Normally when I see a squealing serpentine belt and poor charging I would assume the belt isn't tight enough and call it a day. But....

'92 XJ with 4.0, 118K miles:

I just changed the belt a few days ago and it's been noisy ever since. I have a little bit of rubber on the alternator that is coming from the alternator pulley/belt, peeling off the belt, so I know it's happening at the alternator rather than at one of the other locations. Just in case today while it was idling I tightened the pulley down with the tensioner

So- every now and again, maybe 1/2 the time the alternator works just fine, volt jump up and the squealing stops. Power jumps up as well, all of a sudden I have quite a bit more power no matter what RMP range this happens in. Also, the alternator pulley is now polished to a mirror finish on the groves from the new belt sliding over it. I'm thinking this is probably not just a loose belt but rather a partially seized alternator, but I've never had an alternator seize like that, only slowly die from not producing power.

Is this "common" enough that I should try a new alternator? I don't really want to throw money after this when I'm not sure it's the alternator that's bad. Can't get the belt any tighter though-

 

[Midnight Krawler]

Check the harmonic balancer, when it starts to fail the pulley will move out of alignment and start to shred belts. This is a common failure. Do a search on harmonic balancer.

 

[Jess]

sounds like the alternator has dirty brushes, however over-tightening the belt will cause damage to the other components driven by the belt (water pump, ac compressor, etc.)

 

[carnuck]

If the belt is too loose, the alternator will pretty much stop moving until it heats up enough that the belt shrinks and it grabs the pulley. Rubber is the only thing I know of that shrinks when heated and expands when cold.

 

[buffalomatt350]

Take the belt off and spin the alternator pulley. It should spin smoothly without making any noises and without much resistance. That should help you decide if your problem is coming from the alternator.

 

[TiRod]

The local parts supplier should be able to do a diagnostic on the alt to see if it's functioning - at no cost. In the car. Should the harmonic and other pulleys appear to be in line and in good working order, give it a try.

If it's got over 130k miles, the alt may need replacing. That seems to be about when they go in general.

PS I'm sure you've double checked to see the belt has the correct number of grooves, etc. Sometimes parts guys grab the wrong belt on a busy day.