atb

Anyone know what the life expectancy of the cam gears are on a 32V motor?

It seems in the Pac NW here that the issue of replacing cam gears has become more prevalent. I don't know if its just because most of the engines seem to be getting beyond the 100K mile mark, or for some other reason.

I started a T-belt replacement the other day, and was suprised to see the passenger side cam gear badly worn, with part of the driver side gear starting to show wear. The crank and oil pump gear appear fine. It was a little deceiving because gears were a little dirty, but when I wiped the teeth with a cloth it was clearly evident.

Anyone who is doing their T-belt change should definitely take some time and closely inspect all of the gears driven by the T-belt. Take time to wipe off the teeth and see if the anodization is gone. It's easy to tell once the teeth are wiped because they will be very shiny/polished. The anodization is very dull looking in comparison.

So to sum up:

Shiny = time to replace
Dull = good to go.

atb

I forgot to note that my motor has about 145K miles.

PorKen

I've assumed it's mostly a factor of (over)tension.

Leaky oil seals plus dirt might make a nice grinding paste on the belt. Or perhaps the incessant PacNW dirty rain water is to blame.

heinrich

Agreed with Ken. I have had to replace a few, and it appears that was accompanied by a forward-riding belt, at least on my '85. On the '87 I replaced only one, but who knows if one had been replaced at an earlier point. Other was fine. Shiny = bad.

mark kibort

i had 2 928s, all with high mileage, all the pulleys are great. my first race car was 175,000miles and most of the last 40k was all racing!!
cam pulleys were perfect.

Its due to over tensioning i would imagine.

Mk

Jim_H

Over tensioning gets my vote, for what it's worth.

Jim_H

Adam,

How many of those 145k miles are you responsible for?

atb

I was good for the last 45K. I had the dealer install the current belt when I first got the car (feels like a million years ago, I can't believe how much I've learned abou these cars since then) and brought it back for a re-tension after the first 1K. In the last 9 months or so, I would get a t-belt warning when I floored it under heavy load at low revs, like going up hill. The light would come on just as the needle swept past 5.5K rpms. I rechecked the tension several times and it always was in spec. Just before the Track Attack I checked it and it was loose, for the first time. I re-tensioned it. My first two attempts were too conservative, my third time I overshot. The fourth time I backed it off and it landed right on the mark. I handcranked to motor four revolutions and re-checked, still spot on. This was back in April, it seems hard to believe that the kind of wear on the passenger side gear is all from two months of driving. The driver side gear is only worn on about half the teeth.

I had the kempf tool calibrated with the Porsche tool, which confirmed the marker pointing to the tension side of the notch. I will probably go just a little shy of this on the new belt and see if I get any tension warnings.

PorKen

I wonder if a dud tensioner thermo-washer pack or low/no tensioner oil would contribute to this problem?

IE. if the washers are flat, and the tension is set cold, when the engine warms and expands, the tension goes high.
...

atb said: "The driver side gear is only worn on about half the teeth"

I bought some junk HTD gears off eBay; totally worn out. You could see the valve operation in the amount of wear at different angles on the gear.

atb

PorKen wrote:

That is very possible. After reading all the posts about tensioners being neglected when the t-belt/water pumps were replaced, I checked the level in the tensioner. It was empty, or darn near. It took much pumping of oil into the input together with a mighty vac on the drain port before the oil starting coming through. It took a lot of oil. I did this about 6 months ago in hopes of solving the t-belt warnings I was getting. It worked for a bit.