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.

KVDR

Do you have AC on? Try switching it on or off to see if the sound goes away/arrives. That would indicate the alternator/AC belt.

Karrera Coupe

Thank you. I will try it.

PaulD_944S2

Sounds like the multi-rib belt that runs the AC and alternator. Alternator has to charge the battery right after starting so heavier load causes belt to slip. Re-tighten, if it continues to happen, replace the belt.

Better yet, just replace the belt.

RajDatta

As stated, possibly the belts or you could have one of bearings on its way out. Could be the alternator or AC compressor bearing. If you are not using your AC, try using it to help lube the components. The system has oil and its circulation might help not just with the noise but also keep the seals well lubed.
Did they change all the rollers as well? Were quality components used? Is the WP rebuilt unit? Bad bearing on the WP? Could be lots of things. Try getting a mechanics stethoscope to narrow down the noise.

sm

Try removing the alternator/ air con belt and see if you get the noise the following morning when you fire it up. If no, that's your issue. Tighten the belt using the tensioner strut, but remember one end of the strut is REVERSE threaded. Look at the threads to identify which end - I can't remember.

Karrera Coupe

Thank you all for your advice. As luck would have it, this morning it started up for the first time in quite a while without any noise at all! I was standing there ready with my IPhone to record the noise so that I can play it back to my mechanic. Maybe that it is the solution!

I will adjust the ac/alternator belt and if that does not help I will to try the mechanic's stethoscope - nothing like a great excuse to buy a new tool.
Thanks again - when it is solved (I am hopeful) I will post the solution.

V2Rocket

If the power steering pulley has a bit of rust on it, it can make a f***ing terrible noise.

Paul Waterloo

When adjusting it, make sure you follow the procedure on Clark's garage....it's best to loosen all the components first, extend the arm, then tighten all of the component bolts again. Otherwise they can literally break the heads/studs on them. Happened to me on my 968 and recently on my 944T! And I thought I did it right!

RajDatta

Good point. Always loosen the pivot points before adjusting belt adjusters.

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.

thomasmryan

it is typical for some to 'try' to adjust the tensioner without loosening the pivot bolt first. I wouldn't finger point at your mechanic unless he was the only person to ever touch the car. I refuse to work on others peoples vehicles specificly for that reason.

griffiths has oe and a more modern unit available.

Karrera Coupe

Is there one or two pivot bolts? From the drawings it looks like two, and from looking at the compressor it also looks like to two.
Since the WP, TB etc. work was done no other mechanic (or I) have touched it. So I am still trying to figure out if there should be two pivot bolts. If so my mechanic must have been the one to not re-install one of them.
As from the date that I bought the car until the day the WP, TB, engine mounts were replaced, there was no screeching noise.
By the way when I refer to my mechanic, it is an independent German imports shop, not a one man show.
Thanks for the input.

Jay Wellwood

Another shameless endorsement of the griffiths products.

Karrera Coupe

Problem solved! My mechanic replaced the AC compressor with a brand new Denso and installed new Serpentine belt and new power steering pump belt. I a very grateful that he did the honorable thing without any debate. My new old 968 is no longer screeching and is now a pleasure to drive again. Thanks for all the advice and suggestions.