4.8i a/c belt squeaking

[andrewwynn]

Replaced ≠ fixed. Three symptoms do point to the harmonic balancer or tensioner but have you ever tested with belt off and warm engine already squeaking? You definitely want to isolate the source and I would try that for sure; ac belt off also.

A used balancer will be stiff when cold it would be impossible to tell if it's problematic. Do you have welding capability? You can weld the inner/outer parts of the old balancer and try it. Might be slightly noisier engine but without the squeak if that was the source

[andrewwynn]

A client car had a tensioner that was worn on the pivot point to where it was bent 2-3° and causing the belt to ride off the edge of at least one pulley.

I removed the tensioner and used a right angle grinder to bevel the face that mounts to the "engine" (not sure if actually the block or what), and got the thing to pull straight again.

Back to topic: I would use a microphone on an earbud wire etc and an app that does FFT: you will see the exact spike in some frequency related to the squeak and makes it super easy to find.

An example: I was using an air compressor and was hearing a strange noise like a mosquito; it bounced off everything so I could not tell the direction of the source at all!

FFT caught the exact tone and I just waved my phone around to home in on the source: was a hose fitting that didn't have enough Teflon tape.

https://apps.apple.com/gb/app/fft/id298840058

That is the exact app I use.

This is another option I think it's cheaper maybe free (odd thing with  app store is that it doesn't show price after purchase).

https://apps.apple.com/us/app/sonic-...m/id1245046029

[Cyrix2k]

Originally Posted by andrewwynn

Replaced ≠ fixed.

I agree. I just expected the symptoms to change after replacing it if that was in fact the culprit.

Three symptoms do point to the harmonic balancer or tensioner but have you ever tested with belt off and warm engine already squeaking? You definitely want to isolate the source and I would try that for sure; ac belt off also.

A used balancer will be stiff when cold it would be impossible to tell if it's problematic. Do you have welding capability? You can weld the inner/outer parts of the old balancer and try it. Might be slightly noisier engine but without the squeak if that was the source

I'll try that later this week - it's too cold outside for it to reliably act up right now. I can weld and that's a great suggestion.

[andrewwynn]

I hope it helps. I have a spare h b from m62 I believe. Before you buy another used one let me know if the weld trick pins down the source and I'll try to track mine down you can try before you buy just pay shipping.

[Cyrix2k]

I solved the problem! You're never going to believe this, it was a missing vacuum cap on the vacuum pump It's been missing since I bought the X5 and I never gave it a second thought until a friend mentioned it. I looked it up on the ETK and sure enough, BMW has a part # for a cap. Part #4 below