993 Alternator Belt keeps breaking - Help!

[SP2]

Hello,
I have a 1997 993. I have had 3 belts tear in half recently. The first happened about 2000 miles ago. It was professionally installed. After it broke, I installed the second one myself. It lasted about 2000 miles, then broke on a cold day. I installed a new one today (the third one) and it broke in about 40 miles. They just seem to snap in half.

This third belt, I tried putting one more shim in between the two pulley halves. So I made the space between the pulley halves wider, and I thought that would put less tension on the belt. When I started the car, and then turned it off, the belt would deflect about 1/4 inch, but it seemed tight. It is a 760 mm belt.

I am worried that this is a sign of something more sinister lurking. Any thoughts? I have another belt ready to go in, but I don't want to keep doing the same thing wrong. I appreciate any advice.

Thanks!

[Don Plumley]

Do you have the update kit installed? Sounds like the problem.

[kurquhart]

Here is the relevant TSB:
http://www.993faq.com/archives/cat_engine.html#000129

[kang]

Also make sure you are using factory belts.

[TCallas]

Hello there, If all is correctly set and you are utilizing all factory parts including the drive belts, I have had this problem caused by an intermittently faulty cooling fan hub bearing. When replacing your drive belts on a 993, they need to be very tight (I call this banjo string tight), they need to be factory Porsche drive belts AND all the parts, especially the shims need to be in the correct amount and order. If your drive belts are adjusted too loose you will likely get a check engine light due to OBD-II misfire fault codes.

[SP2]

Thanks for the advice guys. I will be installing a pulley upgrade. Why are the Porsche factory belts so important?

[TCallas]

There are other good drive belt manufacturers on the market i.e. Continental (Conti & CRP), Gates and others but these other belts have a tendency to stretch immediately and also not fit the Porsches 100%.

[Leo O'Farrell]

Are all three belts to be Porsche? I purchased belts but haven't installed yet, the two small belts are Porsche, the large one Continental. Is this set up OK?

Thanks.

Leo

[Don Plumley]

The critical belts are the alt and fan belt. Probably much less of an issue for the AC belt.

[TCallas]

Off the record, I think it's OK to use a Continental drive belt for the A/C Compressor even though I still choose to use the factory brand only.