I saw a notification from Porsche that the chain tensionner has to be replaced at 200 000 Kms. But, considering 944 s Failure, I would say, replace the upper pad part at 100 000. I did it on mine, it was clear that was the good choice as the upper pad was marked. The lower one was almost smooth so it wasn't necessary to change it. Just my 2 cents for preventive works to do!!

In reading most of this thread, I may understand that 944 S pads are the same as 928 pads. And the lower pad is available for the 944 S as they do not exist in the 928 catalog. Am I Right? That is true that it exists a refs for tensionner rebuilt I did not really know what it includes. Do you Know? Is it the kit which contains pads lower and upper?

Thanks

Puyi

 

I don't know if anyone is still subsribed to/reading this thread, but I found it very interesting. I'm considering purchasing an S4 and having owned several DOHC 944-series cars, I thought that I'd better check up on this.

I think I have an article scanned from an old "911 & Porsche World" magazine that had a lot of photographs of an S2 motor with something over 100K miles (IIRC)....maybe significantly over... and the cam chain/tensioner system was being R&R'd. The upshot of this article, with pix to illustrate, was that the sprockets (gears??) on the cams were REALLY worn down--they compared them to sprockets on a new camshaft, and it was disturbing at the degradation on the cam sprockets. (I don't really know what would be the ultimate consequence of letting them go further---breaking teeth? Or would the chain finally just slip off the sprockets and start flapping around?) Bottom line was they had to replace the camshafts as well as the chain.

I haven't quite grokked Dr. Bob's analysis of why a new chain would localize the wear on both components, but I believe him ;-)! If he is correct on that then his recommendation of either "never" or "very often" makes total sense.

If one were to choose the "very often" path, then what would be a reasonable definition of "often"? Again, IIRC, that article recommended new chains every 60-75K miles, implying that within that time, no significant cam sprocket wear would occur. Whether this is a short enough period or not, I have no real data aside from this article.

I think the chains themselves are relatively cheap and I know that camshafts are NOT. The variable I'm missing, due to lack of experience, is the cost/hassle factor of removing thecams to replace the chains. Depending on this, perhaps, if you have a low-miles car, it MIGHT make sense to do the "very often" approach if 60K-75K is "often" enough?

Also, if there ARE "safe" chains with a master link, that would make the idea of "very often" more appealing.

If you have a car with over say, 60K-75K miles, or the cam sprockets have already been worn down some, then there's no real advantage to changing the chain and the best thing to do is monitor pad wear and replace as needed, and replace the chain (and cams!) if they seem to be dangerously worn.

This is a fairly big topic in the 944S2/968 groups, but I really hadn't heard anything in the 928 forum since I started participating--until I ran the search. It does appear that it seems to be much less problematic for 928's for some reason.
I'd love to hear from Bill Ball and others who have really high-mileage cars and see what their observations of this situation might be.

 

I took the ones out of my car at 136,000 and there was no wear to speak of in the chain.
I can push the links together and pull on them and get no movement that I can see, which means the pitch length has not changed from new.

The pads were a different story, very worn, one on each side.

Use the factory chains from one of our suppliers.

 

My GTS is at 63k miles I wasn't thinking about this until it hit many more miles. here is a picture of my 944S2 at 110k miles. I replaced the entire tensioner since I could not find the pads alone. There appeared to be no signs of wear other than the pad Although the pad was fairly well worn by this time. I am wondering if I need to look into this at 63k miles or is there a specific interval we should be changing them at?

 

I went back and pulled up the article I referenced above. Turns out it was from the December 1999 issue of 911 & PW Word magazine! (Unbelievable!!!).

I'm definitely and obviously not an expert on this topic, nor any other on these cars, but I will quote some of the info relevant to this thread contained in the article.

After discussing the general layout of the cylinder head and camshafts, and explaining the problems with the nylon "slipper" cracking and breaking up, the author states:

"And that's by no means all. Regardless of whether or not that nylon slipper starts to break up, the chain -- which with only a single row of rollers isn't exactly over-engineered -- will inevitably begin to wear and stretch. Yet again this isn't in itself a big problem -- it's what the tensioner is there to compensate for, after all -- but eventually this does start to have quite serious effects on the camshaft sprockets.

"As the chain stretches, so the distance between the indivual rollers gradually increases. And as the sprockets wear so what is known as the chordal distance between each tooth decreases. The result, thanks to the immutable laws of geometry (and compounded by the fact that the tensioner is continually pushing the top run of the chain upward, away from the sprockets), is that the approaching rollers impinge more heavily on the teeth than either was designed to cope with -- and something has to give. [Dr. Bob--true/not true?? --stp] Either the chain breaks, in other words, or one or more the camshaft sprocket teeth breaks off.

"If it's the former the results will be much the same as if the tensioner breaks up, but surprisingly a broken tooth will often fall harmlessly down onto the cylinder-head casting. Indeed, it is a measure of just how tolerant these camshaft sprockets are to the most amazing abuse that they can reach the stage shown in the photo at the top of opposite page. What had once been sharply defined teeth were no more than vague bumps -- and the engine from which this camshaft was removed was still running.

"Trouble is, though, that the sprockets can quickly wear to the point that fitting a new chain can only ever be a short-term solution -- and in some circumstances might even exacerbate the situation. 'Anyone who's owned a motorcylce soon learns that ou never change a driving chain or a sprocket on its own, argues Barry Hart' [The mechanic working on this car --stp]. 'If one is worn and the other is new, the worn part quickly wears out the new one, and you're back where you started. You should only ever change both parts together.'

[In this article, the author and mechanic don't follow their own advice--they didn't change the sprockets because of the expense of new camshafts. They decide to just replace the chains "often" in the future. Also, remember this is an article about a 944 S2. It may not even be totally applicable to the 928 heads. stp]

"It was obvious by now that both our tensioner and chain would have to be replaced (the stretch in the latter was immediately obvious from the extension of the tensioner's central piston), but even at this point I was confident that the sprockets would be fit for another tour of duty. They certainly looked serviceable to my untrained eye.

"But Barry Hart wasn't so sure. Having analysed hundreds of these engines...he now routinely checks the dimensions of the teeth with a micrometer...and, if they fall outside a range of closely guarded figures, [Empahsis mine and: Gee, thanks, Barry stp] suggests that they should be renewed.

"It was at this stage that I started to become a little anxious .... Each sprocket is an integral part of the camshaft and at best we would be looking at a bill of 900 pounds sterling to replace them....

"And Barry's initial findings...did nothing to ease my stress level. The sprocket on the exhaust camshaft was about 75 percent worn, but that on the inlet camshaft (probably because it's the driven rather than the driving shaft, argues Barry) was on the borderline. In the end, Barry himself suggested -- with no pressure from me, I might add -- that we could use it again, [Why--if all preceding is true?? --stp], and I for one sincerely hope that by renewing the chain at fairly regular intervals from now on, we can preserve the sprockets more or less indefinitely. Time alone will tell!"
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I don't know the mileage on the S2 head they used in this article. Maybe it was REALLY high which would explain the wear on the sprockets. And if even this extreme sprocket wear doesnt' warrant new camshafts/sprockets, well, it may not really be a problem at all. It may also be that there is some difference between the 944S2 and the 928 heads that make this even less of a problem.

Anyway, I hope this contributes some additional information to this thread and that others more knowledgeable than I might have some comments on this information. If there's something fundamentally in error in this I'll come back and delete it forever!

 

IMHO with the age of these plastic parts they should be changed when you go in there to redo the valve covers etc. Even if there is no wear to speak of.

I have removed some with over 300k km on them with no sign of them ever being changed and had really very little wear on them. But one tiny little shock and that old brittle plastic just disintigrated.