Eturtle

I just recently purchased my '98 z28 M6 and always heard a very audible chirping from the belts when it was first started in the morning. It would warm up and pretty much go away completely. I went underneath the car with it running and could tell it was from the A/C belt. I determined in was the lower pulley and promptly replaced it. Turns out I was wrong. I double-checked the upper idler and swapped it with the lower idler, which turned out to make it worse.
After very careful examination I found the reason for this thread. The belt was rubbing on the back of the crank pulley enough to have polished just inside the lip and there was corresponding damage to the edge of the belt. It appears that the A/C compressor pulley is back just enough to pull the belt a little too far towards the engine and cause the chirping. I decided to take some red scotch brite material to that lip hoping it was just all the rust causing issues. Just for good measure I also sprayed the pulleys with brake cleaner to make sure no lubricants were contributing.
Since the compressor is not adjustable the only real fix I can think of is to remove the pulley and remove some of the lip to that interference is not possible.
It appears I have cured my issue, but the real test will be the cold start tomorrow!

SVTconfused

id try to tighten the crank pulley bolt more if im getting the right mental picture...

Eturtle

I did consider that, but the crank pulley has never been off. The alignment for the other belt is perfect, same amount of space on either side of the pulley lips. My thought is that the A/C compressor has been replaced and maybe its just off enough to create the problem.

Eturtle

Update: The noise was greatly reduced this morning and went away much sooner. The difference was the end of my street vs the noise not stopping for 5-6miles down the road and was much louder.

A different belt that was 1-2mm skinnier would eliminate the problem completely. Not even a different part number but just the difference in the manufacturers.

jrob56

iTrader: (39)

Ya ive got this 5-6 mile cold start squeal as well. Sounds like its from ac belt in my case too. I recently did a udp and new gator belts. Ill have to take a look at it

chrysler kid

iTrader: (14)

had the same problem on my truck. replaced the ac belt tensioner and the belt itself. When the belts get old and slip slightly they make the squealing

jrob56

iTrader: (39)

I just pulled my belt and no more issue, so its def AC related. Edge of belt in a couple places is worn to the string on the sides. So i guess it could be the same issue. Dont know how to fix it though.

Might go swap the ac tensioner bracket with one my friend has to see what happens. My question is why would it stop after warm up if it is an alignment issue

chrysler kid

iTrader: (14)

When the belt gets too hot it can get Glazed and the rubber becomes very stiff, when the cars been running a while the belt gets hotter and it is easier to spin because the rubber isn't as hard as when it was cold

The edge was frayed on mine as well. If you can hear a rattling coming from the engine bay it is the tensioner spring. The belts are about $8, I would just replace your old one and just monitor it when you do oil changes to check for any abnormal wear

Eturtle

I completely addressed the issue this evening. I would like to say that this belt is not very old, the part numbers are still clearly even!
I'm not sure that I'd recommend this fix to anyone who isn't very cautious.
I removed the A/C belt, put the other one back one, and started the car. With an assortment of files and grinding bits I simply pushed them into the lip that was the issue. The grinding bit was by far the most effective but by no means fast. I finished with a mill file I swear was doing next to nothing. The end result was very smooth. This took care of the lip by "pushing" it over perhaps an entire 1/16" at best. It does fix the actual problem of the belt touching the lip transitioning from crank to idler. Like I can see light between the 2 now.
If I was to be technical and really safe I would have removed the crank pulley, put it in a lathe, and turned down the lip the 1/16".
My method worked for me, as always YMMV. As usual I shall check it again once the car is completely cooled overnight and report back.

Eturtle

Jrob I haven't figured out why it eventually stops either. I presume it's a temperature thing. Maybe the belt stretches a little more or just becomes more pliable.

dtws6

I'm having the same squealing issue. Is the A/C tensioner supposed to be spring loaded? I have to loosen the mounting bolt to take the belt off and manually push the tensioner to tighten the belt.

Eturtle

The A/C tensioner as well as your other belt's tensioner are very much spring loaded. You should NEED a 15mm wrench to loosen it. If you're manually pushing anything to tighten a belt the tensioner definitely needs to be replaced.

jrob56

iTrader: (39)

I popped my belt off like i said before and the sides were worn, I threw it back on because I didnt have time to deal with it really. Much less of an issue, might have a min of very slight almost unnoticeable noise now and its gone. Guess the sides of the belt are wearing down. Hopefully it cures itself ha.

Eturtle

Problem fixed! Started the car up this morning and there was absolutely no squeal at all. It never started to squeal during the drive either. I am very happy.
Jrob I think I also came up with the answer to why it stops after its warmed up. A brand new belt won't squeal it because its rubber edge hasn't worn-off, once it does the polyester cords are showing. Either the cords themselves or the open gap between rubber cause the squeal. So as the belt spins off the pulley it goes rubber/polyester and back to rubber.
The sound goes away after the belt has warmed up because the rubber becomes more pliable/ flexible and no longer pressing the belt against the pulley with the same force.
Everyone's first fix for this is to buy a new belt, but I'm convinced now that is not the issue.