My daughters 2008 Xterra had the alternator fail. I had it replaced and we drove home, about 3 miles. When we started the car up again there was a knocking (metallic in sound) coming from the engine. When I looked under the hood I saw the at the serpentine belt was not on the pulley for the a/c compressor correctly. About half of it was off ( of the seven grooves four were off and toward the body of the compressor. We took it back and the mechanic put the belt on correctly. He then diagnosed the knocking noise as " the a/c compressor bearing have gone bad and you need a new compressor" (paraphrasing). My question to the forum- Does this seem reasonable or could the mis installed serpentine belt caused extra strain on the pulley shaft and caused the failure. Thanks for any help…!!
Seems unlikely to me.
a bad a/c compressor can cause the belt to slip off. but the belt should not cause the compressor to fail. did you hear any noises from the compressor before this all happened? they should have also changed the belt tensioner and idler pulley with the new belt.
I am not a mechanic but I’ve done some reading and it’s apparently possible for a bad bearing to cause a serpentine belt to become misaligned. That would make this a case of chicken vs. egg: The defective compressor could have been responsible for the belt rather than the other way around. It does seem odd to my nonmechanic mind that the shop wouldn’t have caught it when the belt was replaced.
Seems unlikely to me, too. Coincidental failure… the Mechanic’s worst nightmare.
Thank you for the replies. What a great group…!!
Whenever I have a drive belt off I turn all the pulleys by hand (except the crank pulley of course!) to check for smoothness and side-play.
Very smart. Thanks.
An experienced and attentive mechanic would never let a problem like that get back to the customer unannounced.
In my opinion the misaligned belt could not damage the bearing while a misaligned idler or tensioner pulley could and would allow the engine to start and run normally(quietly) for a short distance before jumping a load carrying pulley to become noisy but still not damage the compressor bearing. When a belt is removed every pulley that it aligns with MUST be turned to feel for play, drag, etc.and once installed close attention must be paid to the alignment of every pulley while at normal operating RPMs,