Whining noise, thinking the fan pulley?

The past few times that I have had my XJ running I have noticed a high pitched whine that sounds like a police siren. After popping the hood I noticed that the belt wasn't exactly on the fan pulley and it sounded like the sound was coming from that pulley. It looks like the belt was sliding off the back:



The belt was riding on the black line real close to the side of the pulley


Could the pulley be working it's way away from the engine? Or is that where it usually rides in the first place?

From my searches I have found that the idler pulley goes bad quite a bit, does that sound like the culprit to anyone?

Thanks

Nice little $20 tool in the chest for this stuff is a mechanics stethoscope. I found a squealing ps pulley on my Cadillac last week with mine. It was rust on the outer bearing surface and I could only isolate it by probing the outside lip of the race.

I just had the same exact sound coming from the front of my engine last night. I changed the idler pulley. $20 at Advanced and ~15 minutes and sounds good as new.

Also check that the harmonic balancer is not separating.

I bought the mechanics stethoscope this morning, so I will put it back together tonight and start probing for sounds.

Should I be worried that the belt was riding near the back side of the fan pulley?

How do I check the harmonic balancer? Try to move it back and forth?

Thanks!

don't worry about belt at rear of pulley, the block will stop it

Thanks for the pulley info ehall.

I cleaned up the fan pulley, bolted it back on, installed the belt, and ran it last night. It was humming decently loud on and off for the first 5 minutes, but now the sound is gone? I drove around for another 15 minutes, gave it a few WOT pulls, and still no whining. I don't believe I fixed the problem, so now it sucks since I can't hear where it WAS coming from.

As for the mechanics stethoscope, where to you put it to hear for vibrations to test the fan pulley,idler pulley, water pump, while it is running? I tried it on the A/C compressor and power steering pump and did not hear any loud noises coming from them.

Thanks!

Hallo. It is better to remove the belt and listen to the bearing areas. You will not hear squeels , but grindings when worn out.
You can turn most of the pullys easy by hand except the harmonic pulley. haha :listenmus
Also look for any play or movement.

'92 XJ wim