This is a 92 968 with about 140k. We just replaced the timing belt that had about 20k on it, because the belt was getting damaged due to the belt riding forward on the waterpump. Less than half the belt was left on the car, and it has actually jumped a tooth on the cam. It lost power, and that is how we found the belt damage.
When the belt was changed prior, all seals and rollers were done, including the tensioner chain and pads.
We looked, and couldn't find any obvioius signs of anything out of the ordinary. We did replace the timing belt crank pully, since it did seem to have some wear.

Here is the belt after 100 miles. As you can see, the forward edge of the belt is wearing again.







Anyone have any idea why this is happening?
We do have another 968 to compare against, and the only thing we have found, is the water pump casting is stamped 2.5 instead of 2.7. The owner had been informed that all the new pumps used the 2.5 casting. I have my doubts, but regardless, the pully size and position both match the measurements we took from the other car.

 

You are probably missing the alignment spacer between the crank pulley and the alternator pulley. There is supposed to a big washer that acts as a spacer to stop the timing belt from rubbing on its front. The rear is controlled by the lip on the crank pulley.
Whoever did the front seals, seperated the crank pulley from alternator pulley and forgot to install the washer. I always try to remove all three units in 1 piece.
As far as the WP saying 2.5, it could potential give you flow issues. You need the 2.7 stamped waterpump.
Please confirm that this spacer is in place and not missing. I can try uploading a picture for you later.
Raj

 

Yes, the washer is in place, that was my first thought. The whole area has been cleaned, so there isn't any crud making anything sit crooked.
On the other car, there is about 1/8 inch of space between the belt and the front of the wp.

Tension has been rechecked with the porsche tool to confirm the tensioner is working correctly also.


Thanks,

Tom

 

When my sprockets went bad it put enough pressure on the forward edge of the belt to break the thrust washers, and throw the belt off. This was just the balance shaft stuff though...
They were probably never replaced before, but when I changed them all problem was solved. The BS belt may also have been way over tensioned before I got it causing it to pull the sprockets in....

...Anyway... Just thought I would share.

 

I would have to think, it's your waterpump then. Think about it, most 2.5 liter engines used a much narrower timing belt (2 valve heads). 89 on S2 and 968's use a much wider belt with exception of the 2.7 na, which is still a single cam application.
Regards.
Raj

 

That is exactly what I have been telling the owner. But the pulleys measure out the same as each other.
I am going to try to check it against my S2, and see if I see anything else. I might try to talk him into replace the waterpump and trying that out. I figure I have a good used one, and it has the 2.7 stamp.

Has anyone else ever heard of this same casting for all the pumps? Anyone bought a new pump for their 3 liter recently that can check?

Thanks,

Tom

 

I did a timing belt and rollers on my 968, and immediately the belt started riding forward on the camshaft pulley. After much trial and error, I discovered that the copper (or whatever) sleeve on the tensioner pivot arm was worn and the tensioner arm itself has play. I am able to move the arm in and out just a bit, but if the arm is pulled out a bit, the belt rides out ( or the other way, I cant remember for sure). If it is the other way a bit then it rides normally. Check for in-out play of the pivot arm by gently pulling in and out on the end that has the tensioner roller. If it moves then start the motor with it one way and see if the belt rides properly on the cam sprocket. If not, then move it the other way (it should not move much) and start it again to see if it rides differently. I really need to replace the copper sleeve on mine, but since I positioned it properly, it has stayed on the correct path.

 

Interesting. How did you find the wear on the sleeve? I am going to check this out this weekend. Looks like Porsche sell the whole arm as an assembly.
I know those stupid o-rings on the piviot stud are a serious pain!

 

I cant really see the wear on the sleeve at all, but the arm has movement when it is installed. I suppose the wear would be measurable if I had tools to do so, but I do not have them. I tried changing out the o-rings and even making a washer for the other side because I was second guessing myself about how it should be assembled, but nothing made it any better. Someone had mentioned replacing the sleeve but I never looked to see if it was available anywhere.

I did have a bit of trouble with the o-rings but some lube helped get the arm over them properly. Everything seemed to fit tightly, but with the tensioner still off and the pivot arm fully installed, there is definite in and out movement at the upper end near to where the roller is attached.

How much is that arm? Probably worth replacing mine since a belt failure is so catastrophic.

 

Which way around is the crank pulley? It has a lip on it.

 

Tom, the 968/S2 replacements always say 2.7 on the waterpump.
Raj

 

Actually, the crank pulley does not have a lip on the later cars. I think its only on earlier cars.
Raj

 

Not sure one the price on the assembly, but I am sure I will find out soon!

Speaking of pulley orentation, which way should the lip be on the tensioner arm itself? I believe we have the lip towards the rear of the car.

What are you guys using to compress the tensioner itself?

 

I made this tool for myself:
https://rennlist.com/forums/968-foru...sion-tool.html

 

Sweet looking tool! I have been using a disc brake spreading tool. So far it has worked pretty well. Seemed to make sense, and it works just like your tool, so I feel better about it.
http://cgi.ebay.com/ebaymotors/Brake...-/170394125953


Dunno if I am going to go look at the car this weekend. The owner is in his first week of quiting smoking, so he is a bit grumpy. If I go there, I might have to buy cigarettes to throw in the other direction so I can actually look at the car!
But I guess that isn't very supportive.