What could have caused this? (drive belt/pulley issue)

[5zigen]

Today I was driving and started hearing this hellish whine and smelled burning rubber, which automatically made me realize that there's something wrong with the drive belts.

Luckily I was not far from home and drove about another 2 miles back home, which during the time the whine disappeared.

When I got home and popped the hood I noticed that SOME how the nut that holds the idler pulley down horizontally had fallen off, causing the pulley to no longer be fixed to a single point but rather floating there, with the path of the belt being directed only by the remaining tension on the belt+alternator belt.

I replaced the nut and retightened everything, and the belt is still rubbing.

What makes me wonder is what the heck could have caused it to come off? The last time I touched this nut was about 7 months ago, when I replaced all my idler pulleys.

Could it be correlated to me retightening the alt belt from about two weeks ago? Could it have been overtightened, resulting in the extra tension to slowly "push" at the fan pulley, causing stress on the nut and resulting in it falling off?

I would also like to state I do not have a torque wrench or belt deflection meter.

BTW my car is a 1997 Q45 with 108,000 miles on it.

Thanks for any help.
Modified by 5zigen at 4:49 PM 11/17/2008

[maxnix]

I am not sure, but I would be replacing that belt and checking all pulleys soon.

[fixer]

THE BOLT THAT COMES FROM BEHIND THE IDLER PULLEY HAS TO FIT INTO A SLOT AND THEN TIGHTENED, if the bolt is out of the slot then the vibration will eventually straighten out the bolt and the pulley will be loose- - thus the nut will fall off, be careful when installing a new pulley to make sure the bolt is in the slot before tightning. I dont think overtightening the nut will cause any problems besides removal. this is just a possibility

[5zigen]

How do I know when a pulley needs replacing?

[maxnix]

Spin it when free. If it is not perfectly smooth and silent, replace it. Belt load magnifies any imperfections and accelerates wear to failure.

Do get the best quality of bearings (there are 6 total) not the cheapest so you don't have to repeat labor so soon. About $20 (each?) retail.

[Q451990]

My guess is that the bearing locked and the force of the belt somehow unscrewed the nut. Unless it is perfectly smooth and noiseless, I would replace it and the belts... and check the others at the same time... if you have one fail the others probably aren't far behind.

Heath

[5zigen]

Wow you got it right on the head, Q451990. Took it apart today and somehow the seals on the bearings came off thus causing them to seize up and resulted in what you described above. Was not a very pretty sight.

Thanks for the response Maxnix/fixer.

[maxnix]

Replace any bearing set that is not perfect and probably all belts over a year old, certainly two years. Otherwise you will return soon.

Surprised that bearing was not screaming at start up.
Modified by maxnix at 7:52 AM 11/20/2008

[Q451990]

Wow you got it right on the head, Q451990.

I'm glad I could help! Maybe I should expand my title to "Old School and 2nd Gen Q Guru"

Heath