Mitsu

Hi All, I was looking at youtube other day to learn more about 928. There I saw a video clip stating I should not be using Contitech belts because they stretch. Is is true ? It is a bit hard to believe. Do you have any experience on it ? Thanks always for your help.

Schocki

Got my GTS in 2003 and drove it with a Conti TB for 10 years. I can not confirm the claims that I read about Conti 928 TBs in any forum.
Mine required no additional maintenance.
Switched to Gates just because my main supplier has them readily available in 2013 jo issues. Went to a PorKensioner setup the same time and it works well too. I don't think that any of the big TB brands will give you a headache. What gives you problems are cheap water pumps, neglected (not changed) tensioner rollers or insufficiently rebuilt original TB tensioners.

Mitsu

Thanks Schocki ! It was on Youtube "how to change the TB". I thought it was another common sense for 928. Now, I am getting ready for the reground cams to be installed ! 222 intake, 220 exhaust. I will definitely share the result with you !

puyi

Yes very hard to believe, in fact, it seems that this is not relevant. What you have to consider is the profile of the teeth of the timing belt. I have seen several 928 with square profile timing belt that is not relevant for 928 32v. It uses round profile TB's in accordance with the profile of the cam sproket.

Stephane

Mitsu

Thanks puyi for your feedback. I can use Contitech TB with confidence.

FredR

The Conti belt has been around as long as the 928 has and has been used successfully by many including some of our racer friends. it seems to be generally accepted that they are a tad more stretchy than the Gates belt and maybe they are but that means absolutely nothing [to me that is] without some kind of quantitative data. I have never heard of a Conti belt failing because there was a problem with the belt itself just as I have never heard of a Gates belt failing. Personally I use the Gates OEM belt and see no need for anything else but if all of a sudden I needed a new belt and the Gates was not available I would not hesitate to use the Conti belt.

The type of tooth design used in the 928 timing belt changed at some point pre- S4 evolution and this of course meant that the sprockets engaging the belt also changed to what is known as the HTD [High Torque Drive] system but that is not relevant to the "Conti belt" discussion. The HTD system design can be retrofitted to the earlier 928's no problem. I am not aware of any specific problems using the earlier design on the earlier models.

Mitsu

Thanks FredR for your feedback ! it is always good to get a trustworthy comment !

Landseer

Am running Conti, installed by me in May 2008.
At that time I replaced all wear parts in the circuit, which was critical and gives me confidence since.

Have retensioned a few times when triggered by light. Tracking still good. Has about 50 k miles since change. Have a water pump and Gates TB to replace it when I get a window of opportunity. Have gates because 4 years ago I was reading conti disparagement.

Conti good.

Kevin in Atlanta

FCP Euro has Conti belt on clearance for $25.95 now.

hacker-pschorr

I'll only use the Gates "racing" timing belt.
Noting to do with racing, but the idea of having a timing belt that is even a tiny percent stronger seems like a darn good idea to me. In the event that a roller or the WP locks up, this belt might last a bit longer to get the engine shut down before anything major gets damaged.
https://928srus.com/products/92810515750rtb
Years ago when my oil pump locked up I learned what the symptoms of a belt getting shredded are. Thankfully this happened to my US 81 so there was no risk of valve damage as the belt quickly disintegrated.

karl ruiter

I had a 16 valve conti belt stretch on me quite a bit. Not a problem if you have a porKensioner, but this particular car did not have one, and I did not recheck the tension after 500 or 1000 miles. It became quite loose. I don't remember if there was any damage.

GregBBRD

We call them "big rubber bands", since they are so stretchy.
If you have a 9201 tool and you tighten a stock timing belt, it will continue to gain tightness way past the 5.0 belt units the factory recommends. I've tightened a stock belt as high as 9.0, on the 9201 tool, just as an experiment, with no "end" in sight.
With a Conti belt, the tension on the 9201 tools stops at about the 6.0 point and as you tighten further, the tension does not increase, the belt just stretches more.

I guess that there are some good things about this:
1. Tough to over tighten the belt very by very much.
2. The stretching doesn't seem to "kill" the belt. It does stay fairly elastic and if you "back down" on the belt, it doesn't seem to be damaged. Therefore, if you tighten this belt into the "elastic" stage, it might be a longer time util the belt tension light comes on.

The disadvantage to a "stretch belt":
Cam timing will vary because of the stretch.

A stock timing belt retails, from Porsche right now, for $65.34.
Lowest price, in years!

Mitsu

Thanks all for sharing your knowledge and experiences ! I believe all the major brands have different criteria on belt design, but I feel relieved to find they can be used with proper care and attention.

FredR

Good to see some quantitative info regarding the Conti belt. If the thing stops tensioning up at 6 units on the 9201 scale then that tells one where the elastic limit is and by extension the yield point will be just around the corner. I do not understand the scaling of the 9201 tool but assuming tension is directly proportional to the scale value then a reading of 5 for the Conti belt would be fine given general good practice in mechanical engineering circles is to limit service conditions to 90% of yield.

What I do find a little surprising is the characteristic of the stock Gates belt- with such high values it leaves me wondering why anyone would perceive a need for a Gates racing belt given the margins available on the stock item are what they are and the racing belt would presumably be some margin higher..

Given the Conti belt stretches the way it does and presumably stretches more at higher revs maybe that is a good thing given retarding the cams delivers slightly better top end power.

Mitsu

Yes, indeed, we must use them below the elastic limit. The dynamic belt tension always experiences values higher than the static. It is possible to measure the static belt tension by ultrasonic method. But it is not easy to measure the dynamic tension. It can be done using slip-ring and strain gauges, but this is not something we should be spend our effort on, I suppose.