[Karrera Coupe]

About 6 weeks ago I had the TB, WP and engine mounts of my new old 968 replaced. Ever since the work was done a terrible high pitched and loud screeching sounds emanates from the engine for the first two or three minutes after starting up the engine. To me it sounds like a severe case of fan belt slippage.

The sound disappears soon enough but it bothers me a lot. At first I thought it was especially prone to making this noise when cold in the morning but lately it seems to be screeching at any time during the day but only on starting up. I should point out that  it has warmed up very early this year here in Charlotte NC so I no longer think that ambient temperature plays any role, but engine temperature may well have a big influence.

After about 1,500 miles since the TB, WP and engine mounts were changed, I took the car back to my mechanic to re-tension the new belts. I complained about the noise and they asked me to leave the car there overnight so that it can cool down completely before they do the re-tensioning.  Since I got the car back the screeching sound is as loud as ever and seems to even be getting worse.

 On opening the hood while the cacophony is going on, the sound is so loud that I find it impossible to locate the source .Any advice as to what may be causing this and or how to diagnose where the screech is coming from will be much appreciated.

Thanks in advance.

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[ds968]

The screeching lasts as long as two or three minutes ?!! If they re-tensioned the belts correctly, and the screech is still there then maybe one of the pulleys bearings has gone bad , or , possibly the alternator bearings ? Could be simply a coincidence that it happened right after the drive belts and wp replacement - if anything was wrong with any of those components I think after a couple of minutes of that you'd have a catastrophic failure and probably a seized engine by now. That's why I'm thinking it may be a bearings issue . My alternator bearings wake up the entire neighborhood on cold starts ( also for about two or three minutes , and after that the noise disappears ) Is it possible the AC is on ? ( thinking the compressor seizing could also be something causing that kind of loud screeching noise ) . Not that you'd use the AC this time of the year, but in case the switch was accidentally pressed and left on by the shop ..although I suppose you'd notice that soon as you drove the car.. )

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[Karrera Coupe]

Thank you very much DS968. This morning it started up with no noise at all. That was the first normally sounding start up in quite some time. it may have something to do with the fact that it is quite a damp morning here in Charlotte - perhaps one of those bearings or pulleys that you talk about received a little 'lube' from the damp air.

I will be very surprised if the screech does not recur. I will focus in my diagnosis on the alternator and ac compressor. Thanks again so far!

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[Bulti]

Try and turn on the windshield defogger, when the screeching gets worse -or starts- you may have to tighten the V-belt. Moisture can indeed make it slip for a bit at startup. The manual describes how to check the tension. It should be quite tight.

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[Chris Vais]

If the water pump hasn't been replaced that might also be a source of noise. Mine made a horrible sound before it failed. 

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[MCL968]

Before you get any deeper in this, try an old diagnostic trick. Take a bar of soap and rub the underside of the belts where the belts contact the pulleys. This will serve to "lube" the belts temporarily. If the screech goes away, the belt tension or condition is the problem. If not, it may be the alternator bearings or the water pump. I'm guessing, based on how absurdly tight the belts need to be on these cars, that it's the belt condition and/or tension.

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[az968]

The bearings in my alternator had to be replaced last year; the symptom was a continual whine, not just at start-up, so I doubt it's a bearing issue. Since you just replaced the timing belt and the water pump I would do as Matt suggests and focus on external belts, like a/c, PS, alternator.

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[flash]

screech is usually either a loose compressor belt or a glazed one.

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[Karrera Coupe]

Thank you all for your advice and suggestions. Flash I am not familiar with the term 'glazed' as far a belt is concerned. Can you describe such condition?

Thanks again.

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[flash]

as belts age, they get hard.  the cross-linking polymers cause the belts to lose their elasticity.  at this point, when the belt "screeches" it is slipping.  this causes the belt to heat up and harden even more, and often melts the rubber to the point of glazing.  you can see this when you look at the belt.  there is a color change on the contact surface, usually darker than the rest of the belt.

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[Karrera Coupe]

Thanks a lot for all the advice, especially for your explanation about the state of glazed belt Flash. Today has been the second screech free day in  row. I will try out your advice this coming weekend and intend to post an update afterwards.

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[Karrera Coupe]

Friday evening I bought a new Serpentine belt and a new power steering pump belt at my local Autozone. On my way home the screeching became incessant and suddenly I felt the steering get much heavier and saw the alternator warning light come on when the voltage meter dropped. Luckily I was close to home so just kept going and reached home without the engine cutting out.

On inspection the serpentine belt snapped (virtually disintegrated) and the power steering pump belt (v belt)  jumped off the crank pulley.

Saturday morning I started the process to install the new serp and v belt.

As I tried to loosen the AC compressor I noticed that it was already very loose. Closer inspection revealed that the rear mounting bracket at the top of the compressor has sheared off and the bolt on the front mounting bracket is missing. So the ac compressor's only remaining connection is  via the belt tightening/adjustment threaded rod.

To me it looks as if I now need a whole new ac compressor as one of the mounting brackets of mine is torn off.

I suspect the fact that the bolt that should be in the second mounting bracket (front top)  is missing caused to much stress on the remaining bracket and caused it to fail. (1) Is this a likely explanation as to why the rear top bracket broke off?

I am thinking that my mechanic had to remove the serpentine belt to access the engine when he replaced my waterpump, timing belt and also replaced the oil seal behind the crank pulley and replaced the engine mounts. (2) Was it necessary to remove the belts to do this work?

I also think that there is at least a good chance that he then forgot to replace the front top bolt holding the ac compressor in place and that this caused the intermittent screeching when the ac compressor moved on start up while the alternator cause max resistance to charge the battery after the starting draw down. (3) is this assumption likely correct?

My questions to all of you experts is whether my diagnosis re. the forgotten bolt being the culprit for this failure is likely. If so, I will ask my mechanic to help with the cost of the new ac compressor and its installation. (4) Will that be fair?

Thank you all so far and also thanks in advance for giving me your opinion as to whether I am on the right track with my diagnosis and search for the cause and culprit.

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[flash]

this is unfortunately a fairly common problem.  people continually adjust the AC without first loosening the mounting bolts, and/or forget to tighten them back up again.

 

yes, the serpentine belt needed to be removed to do the belts.

 

yes, you will need a new compressor.  you will then, of course, also need a charge of refrigerant

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[Langley968]

968 screeches on startup, then goes away after a few minutes. Found this bolt on the tray when doing the last oil change. Is it from the alternator???


   

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[Kaj Hallstrom]

 Complaint about the high pitched whine when I had the clutch done. Was told it came from the timing belt tensioner..... So what does that mean?...Timing belts and tensioner are new. Look like an investigation  will be starting.

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[JWahlsten]

968 screeches on startup, then goes away after a few minutes. Found this bolt on the tray when doing the last oil change. Is it from the alternator???

FCF4509A-32A0-4CF5-8356-D108093F470F.jpeg

That looks like the bolt from center of the tensioner...  so yes it could be part of your issue.  The bolts on the alternator itself could still be tight masking the issue a bit.

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[Langley968]

Turned out that the bolt was from a support bracket for one of the engine mounts that I had them replace last year. It dropped down, they couldn’t find it, so they installed a new bolt! Hum...

The screach was the alternator. Replaced it with a rebuilt Bosch and all is quiet now!

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[az968]

Nice!

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[Kaj Hallstrom]

I suspect this could be my problem as well. It is so hard to detect as it disappears right away.

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[Langley968]

My alternator was still the original, and after 25 years it was not surprising that the bearings were dried out / worn out. I would have swapped it myself, but the “bolt” question made the local P-shop owner take responsibilty upon himself to solve the mystery, and in the process he swapped the alternator for just the cost of the part!

He’s happy / I’m happy!

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