why did idler pulley self destruct

My idler pulley for the serpentine belt on my 90 xj self destructed yesterday.

First smoke and screeching noise. I pulled over and by the time I opened the hood the smoke was gone, and I couldn't tell where it had come from.

A knocking noise continued and when I pulled to my driveway the thing went crazy with a metal against metal noise.

When I got to look the idler pulley was no longer centered on the bolt

instead there was a large space between the interior of the pulley and the outside.

When I got a new one I could see that the interior bushings with I assume some ball bearings had disintergrated, and disappeared.

I was wondering what could have caused this self destruction.

My best guess is that the rubber bushings had gotten old and cracked, that this created a small off center wobble that heated up and burned the bushings, creating more of a wobble and more heat, until the whole internal bushings peeled away.

The reason I think this is what happened, is because seizing up of the bushing wouldhave had no adverse effect since it ordinarily doesn't move and the interior metal bearing around the bolt was fine.

Any thoughts.

age ... heat .. friction.

Mine squealed on and off for a year .... then finally went south.

The power steering pump is next ... just had to replace it for the same reason.

The bright side is everything runs quieter now ... no squeal, knocking, whining ... the 10 year so-called lifter noise went away too.

Age. You're dealing with a "permanently lubricated" bearing that is going to wear out sooner or later. You have enjoyed a service life of 13 years - for the sort of use these bearings see underhood, that's not bad!

You can save the pully and press in a new bearing for a spare (cross the numbers on the bearing hub) and keep it in the toolbox for a spare on the trail somewhere... I'd expect a new bearing to run about $10 or so, but I've not located one myself yet...

5-90

Yup, they just get old & wear out but they can go in a cloud of belt smoke and lot's o' noise like the motor has just suicided.

If they ever tell ya that your pulley is not available (counter clone using the parts computer)... get another guy cuzz most of them are a standard / generic item that fit more than one vehicle though the computer doesn't show it. XJ's are in the computer, but a van I just bought wasn't. Had to replace the pulley last night after it locked up & smoked the belt. New Guy at Advance looked it up on computer & told me it was "Discontinued... dealer item.", so did the guy at AutismZone... and the guy at NAPA. Then I called the dealer - $160 and only available with the bracket that holds it. I don't think so.
Removed the pulley, went back to Advance, regular counter guy was there & looked at it and said "Oh yeah... we got those." $9.60 for what their computer (and everyone else's) said isn't available. Not listed but it fit perfect.

Bring the pulley in to the parts store with you. If they don't have the one for the XJ, compare to others they have available. Some other apps are real close and will work with a washer or two to shim it.

Attica, IN NAPA parking lot fix. Back in the Badlands within the hour.

anyone know the part number for one? did they change over the years of the XJ. the one on my 2000 has been squeaking for about 20,000 miles so I'd like to change it before it goes boom.

at less than $10 ea from the Zone, I carry a couple spares in my tool box, nothing worse than having a weekend trip ruined by a cheap part.