soontobered84

My '89 AT timing belt was replaced less than 3 years ago. At that time, I replaced all the rollers, water pump, cam gears, etc. Rechecked TB tension at about 1000 miles and everything is good. Fast forward 2 1/2 years while I'm driving down the freeway. I accelerate and DAMN: the toothed belt warning comes on! For those of you who have not seen a digital dash warning like that: It is a red animated function that will really get your attention. I shut the engine down and tow the car back to the house. Pull the right side cam cover, and everything is as it should be. Tension is good. Electrical connection is good. Timing belt appears 2 1/2 years old and good. Tracking of the timing belt appears good. I put it back together and go for a drive. 15 minutes into my drive, the doggone warning light comes on again. WTF? I know the tension is good at this point.

I decide to dig further into the front of the engine and go ahead and replace the timing belt while I'm there. The new Gates belt that I am installing is much heavier/thicker than the Conti belt it is replacing. This got me to thinking that maybe I was getting some kind of rubber band effect from the Conti belt whereby it is stretching out and snapping back like a rubber band. Since I can only check tension when the engine is not running, I'm only seeing the tension when it has snapped back.

Anybody have this phenomena ocurring or shed some light on this?

Bill Ball

Even though there are many cars running around with Conti timing belts with no problems, I had one go limp at about 34K miles with that scary "Toothed Belt" warning pop-up twice in a month. The first time after the warning, I checked the tension and found it on the low end of the Kempf tool window, so I bumped it up a bit. I subsequently ran an open road race at 145MPH average for 90 miles with no warning or other incident. But when the toothed belt warning came on a again a few weeks later while driving sedately around my neighborhood, I changed out the belt for Gates.

I think as a general rule, the timing belt may "settle in" and need tensioning after 1500-2000 miles, and so a tension check is called for by Porsche at this interval, BUT any significant tension loss after that is a BAD sign. These belts are not, or should not be, designed to stretch.

A while back Greg Brown "tested" some timing belts and reported that a Conti timing belt would not increase tension beyond a certain point as he applied increasing force to it but a "Porsche" belt developed more tension with more force (i.e., did not stretch as much as the Conti). I can't find that thread on Rennlist at the moment.

We then argued about whether Gates OEM belts as the same as Gates manufactured Porsche-branded belts. Roger had some interactions with Gates that seemed to indicate the belts were the same. Subsequently, Roger sourced a "racing" timing belt from Gates as well.

https://rennlist.com/forums/928-foru...ming-belt.html

So, make your choice. After my experience, I started using Gates manufactured belts exclusively on my car. Not necessarily Porsche but Gates. I have installed the Gates "racing" belt on other cars but have no longterm experience with it.

cali4sun

This is very interesting. I hope others can share their experiences as well.

'89 S4 GP White/Black
'912E Silver/Black sunroof

Mike Simard

I also have some observations that make me use Gates and not Conti.
When setting up cams on an engine with heavier valve springs and high lift, I noticed a creeping sensation when turning the engine slowly by hand with a Conti. Simply replacing that belt with a Gates gave the turning a different feel with none of the creeping.
The creeping was probably the belt stretching and relaxing, it made moving in small increments 'jerky'.

dprantl

I have had Conti belts loosen themselves after several thousand miles. Also the Conti belt was much easier to install new in my experience. The first Gates belt I just installed a couple of months ago was much harder as it seemed shorter and/or less flexible.

Dan
'91 928GT S/C 475hp/460lb.ft

soontobered84

Bill,Mike, and Dan,
Thanks for posting. I thought maybe I was screwing up somewhere along the line (well, maybe I am, but not in this regard) It's at least good to know that I'm not the Lone Ranger here.

When I took the Conti belt off and compared to the Gates belt, it was substantially more pliable, flexible and thinner.

I will not install another Conti belt, that's for sure.

mark kibort

Ive had great luck with the conti belts. Its all Ive ever used, mostly because I didnt know there were other options. However, no issues in 8 years of racing with them. I can say, i had the same light isssue. changed the wire harness to the sensor, clean contacts, even re used the tensoner when i replace the engine with the stroker, so it got all cleaned up. still the light comes on after 1 -2 mins of driving. Its more than likely a bad contact some where in the warning light system. my belt tension is always set right spec and doesnt move more than a 1/2 point on the scale . (about a quarter turn after a year to retension it up)

mk

soontobered84

Mark,
I was firmly convinced before I took the front of the engine off that it was an electrical issue. However, after checking all the wiring, continuity, and installation, I believe the problem to have been the belt itself. I have replaced the Conti with a Gates belt, which feels much beefier. I am banking on this solving the issues that I was having. Your post further cements that conclusion for me.

Jim M.

Well, Gates is the way to go! I just bought a new Gates from Roger for the low price of $28.50. I'm local so no shipping cost for me.

SeanR

I've had the same Conti on my car for 4 years now and have had no warnings. I do keep the tension on the high side of the Kempf tool, but will most likely change it next year with a Gates since they are cheaper.

mark kibort

I just dont see mine being a belt issue, due to the abuse it sees and its set and checked with both the porsche tool and kempf tool.
The reason I say this, is that even warming the car up with no rpm over 2500, the light comes on at about 3 mins. the reason I know this issue is electrical, is because I then just disconnected the connection and it still has a delay that comes on at 2-3mins after I start driving. Dont know how that works, but its awefully coincidental , dont you think. The only time the light doesnt come on , is when I just short the connection.

These belts are very stiff and it would be very unlikely that the belt is bad fro conti. However, does anyone else see that the gates belt is "beefier"? anyone measure the thickness can show a picture to compare?

Mike Simard

Yes, I measured them.
Conti=.176"
Gates=.190"

mark kibort

cool! Now, is anyone racing with them now? andeson, fan, what are they using? I like to see some race proven experience, before I switch. Its not really the thickness of the rubber, its the fibers inside and the contruction. Plus, a thicker rubber, with thinner fibers could be prone to break. Plus, how the teeth are molded is important too. (more than just the thickness of the belts). You know me, Im pretty skeptical of change, if something has worked as long as it has with no issues. This is such a huge bet, right? engine removal plus half the valves destroyed at $25 each, plus, plus, plus............. HUGE bet.

soontobered84

Mark,
The light will never come before 3 minutes because it is designed to come on any time after 3 minutes if the belt needs tension. My understanding is it was designed this way to allow for startup and expansion, etc. I would bet that your belt is stretching also and rebounding back. Just like me, you cannot check the tension until you turn the engine off. I would be VERY worried if I tracked a car as much as you do with a timing belt warning light coming on. YMMV

Thanks Mike for the measurements. I don't know why I didn't think to do that.

mark kibort

the fact that it acts exacly the same disconnected as connected makes me think electrical, as if it was flapping it might take longer to hit the alarm, due to temp. its always the same. the tension has been the same for 2 years now, no need to tighten, and prior, the other belt was installed with the new cams or waterpump. anyway, 3 years or so, and thats about 50+ races and lots of street miles.

your right, we wont know, so all of this is just guessing right now.

But, i am worried now. thanks for that!

mk