the squeal is unreal

I'm about at my wits end here. I have a 90 XJ that I just replaced the motor. I noticed a chirp from the idler pulley. The chirp quickly became a squeal. So I did what most folks would do and replaced the idler pulley. The squeal was gone for maybe 30 seconds and then was back. The pulley is brand new, so I know its good. I have heard there may suppose to be a spacer behind the pulley, but Im not aware of this. Per the diagram that came with the pulley, the insert goes in from the front. Then the bolt. Anyone have any ideas?

I know from experience, on multiple occasions, a coolant soaked belt will squeal. Seemed worse in cold weather though, so it may not be your problem. No amount of tinkering or adjustment would do any good at all. Washing the belt with hot water, a little dish washing soap and a good rinse helped.

My squeal actually happened to be my alternator. Didn't realize it until I replaced it with the ZJ 136A and now I can hear my exhaust and the valve tick

Belt would be my guess....

Ive got a Chevy p/u that I end up replacing the belt on about every 18 months because of the returning chirping. New belt and all is good for 10-12 months and it slowly comes back.

Go ahead and buy a good quality belt from what ive experienced they do last longer..