964 damper, safe to leave off?

ChrisBennet · ChrisBennet's Garage

Hi everyone,
When people use a 964 motor in a conversion project are they keeping the pulley damper or leaving it off? I've heard of people leaving it off and I think there are pulley replacements for sale that don't use it. Kinda gives me the willies leaving it off.
TIA,
Chris

john_colasante · 06-23-2004, 09:37 AM

Good question. I have asked a few knowledgeable people about this and I have gotten varied answers. Some say you absolutely must have it or you will eventually crack the crankshaft, others say if you blueprint balance the engine you don't need it, and still others say you don't need it at all.

Some of the racing Carrera Cup cars came with a single groove pulley with no rubber damper (I have one). So apparently even Porsche did not find it necessary on that car.

I suppose it's cheap insurance in any case.

mwildt · 06-23-2004, 09:59 AM

Hi,

I assume you're talking about the little rubber ring between the two pulleys ? if so then I think it's there because the pulley speed is different between the 2 belts. One is for the alternater the other one is for the fan. If I recall correct the CUP way is to have only 1 belt is to lock together the two pulleys on the fan/alternator, and then replace the lower pulley with one that only has 1 groove.

There is a switch on the 2 belt/pulley solution that detects when the fan belt breaks.

Michael

Bill Verburg · Bill Verburg's Garage

I would leave it John. Yours is the only one that I have ever seen w/ the single lower pulley, are you sure that it is oem?

The 993 used a significantly beefed up crank to eliminate the balancer.

ChrisBennet · ChrisBennet's Garage

I just got off the phone with a local Porsche guru (Jerry Peligrino, EPE) and he said he has/had 2 customers with 964 Cup cars and they both had the damper.
-Chris

Bill Verburg · Bill Verburg's Garage

Since my original post on the subject, I spent several hours chatting w/ the team engineer/mechanic of a very famous western NY 964/993 racer, we had a pristine 964 Cup car that was the subject(most of the time)

According to him, the damper can be safely left off as on JC's car. The the only issue will be increased NVH.

I would still leave it on as most Cup cars(even the 993s) do have it.

ChrisBennet · ChrisBennet's Garage

Thanks a lot bill.

Now I have (undamped!) oscillationing decisions between leave it off and getting the damper+pulley rebalanced and putting it on.

-Chris

racing97 · 10-19-2004, 06:44 AM

Actually around 1995 Porsche was trying to promote a cup style series here in the U.S. These were "lightweight chassis" and after Al Holberts untimely death the project ended up with Alvin Springer. One of the modifciatons was the removal of the Dampner and I believe it was changed to a Aluminum Poly Grove. That being said it does not make it the correct thing to do. If you were to look at the other end of the crank (flywheel) and take that reciprocating mass into consideration with the pulley in the front and the torsional loading on the back, and If you have substanially reduced the flywheel mass (pitched the dual mass) you should have reduced the need for the torsional offset on the front. I believe this was also done to the Porsche race project but I do not know that for sure.

best regards

JasonAndreas · 10-19-2004, 10:02 PM

Can someone take a picture of the two Porsche tools that are needed to remove the pulley? Assuming the engine is already sitting on a stand how difficult is it to get to and replace the seal & radial sealing ring behind the pulley?