Lizard928

Cosmo's answer is wrong I'm afraid.

At 45 deg non of the pistons are at the top of stroke. So you can rotate the cams as much as youd like and nothing will interfere.

That said, I do all my 32V timing belts at TDC even with big cams and have never had an issue.

Mongo

I don't have a WSM in front of me, but does the factory tell you to rotate to 45 degrees and do the belt also?

Dmhager

Im doing a little archeology dig on a very nicely preserved low mileage 1988 S4 (40k miles). Everything on the car seems original, except for the tires, spark plugs, gas and oil (and everything works). I just removed the timing belt and I am wondering if it just might be the original ... it was still fully intact, but showed its age. It has age cracking all around the outside and some early signs of separation at the teeth. Its a Uniroyal belt (first time seeing one of those), marked with the Porsche logo and Porsche part number. Uniroyal Power Transmission company was sold to Gates in 1986 so I suspect this may very well be the factory original. I think its also interesting to note that the belt was still at the correct tension, the timing gears showed no wear, the water pump and all the other wear items were in good shape. By no means would I ever recommend stretching the service interval beyond the standard, I do find it interesting to see how well this has all held up over the years.

Strosek Ultra

The blue 928S4 Strosek 1987 got a new timing belt for the first time since March 1997. In spite of 22 years and 50.000 km (31.000 miles) the old factory Gates belt looks like all new. I have very carefully examined the belt for wear and micro-cracks but can not find anything. The pulleys show minimal wear and I think they can be reused for a long time. What conclusion can be drawn from this? It seems that the timing aspect of the belt's age is of minor importance. With the tool P9201 I checked the tension of the old belt before dismantling and it was found to be 5.1 units. The correct tension is 4.5 units, so apparently the old belt has been running a little too tight for all the years. The last belt change back in 1997 was carried by a Porsche dealer in Munic, Germany.
Åke

hacker-pschorr

I'd trailer that car to a few high end concourses and win a couple of awards for all in originality before doing the timing belt job


You've got that backwards, if anything the belt could be reused. Rarely in the history of timing belts (all cars) does a belt just up and fail all on its own. Usually something else fails that is in the belt system. Those bearings may "look" fine but the tiny tiny dab of grease on those bearings is wearing thin and when it locks up - good-buy timing belt.

If I had to guess I'd put my money on most 928 belts failing are due to water pump issues.

This is why I'll only be using the Gates racing belt on interference 928 engines. In the hope that if something goes wrong, you'll have a minute or two longer to realize it and shut down the motor before the belt snaps.

worf928

Folks: read the thread. It’s been posted several times: On 928s, The *timing belt* is never the primary reason for “timing belt failure” unless you’re running a belt so old that the surface looks like an oil painting. Anything in the system that the belt touches can be the primary cause. Every part that touches the belt is a wear item and will require replacement at some point due either to mileage or time.

I consider sealed bearings good-enough for a timing belt until they are 10 years old. That means that the main tension and idler rollers are the time-limiting items.

dr bob

Agree on the "support" items, particularly ball bearings and rubber pieces in the tensioners. Old relatively unused bearings have wax where the grease used to be. The liquid part of the original grease has evaporated, leaving just the soap stiffener. Bearings are pretty cheap overall. The drive gear wear is directly related to engine revolutions and speed, plus a K factor for tension. (Coincidence that it's not the "Ken" factor...???). Meanwhile... The belts have plasticizers added to maintain flexibility. Guidance might be the same as we use for tires, where seven or eight years is the practical life limit shared by both the manufacturers and the Feds. After that, the belt is subject to structural cracking and failure. Like the tires, the rubber in the belt is used to distribute the pressure from the teeth, and actually provides the structural components we call the teeth. The aramid cords that are literally the backbone of the belt never fail on their own. The teeth get stripped off after base cracking, a failing tensioner allows the belt to walk up on the gears, a failing bearing in a water pump quickly wears the rubber backing and exposes the cords.

"My belt has been on the car at least seven years now but virtually no miles. Everything looks just like it did when I last changed the belt. Just put a new belt on since everything else is still new, please." Thank you, no.

PorKen

Ha! Recall that before the 928 received its designator, it was referred to as the 'K' type.

Even the Racing belt is not immune to this. This one is eight years old. Granted it led a difficult life before it was stored in a welding shop for a few years, then briefly reused.

Only this one crack in the 'grip' layer (which surprised the 'F' out of me).

NIACAL4NIA

My 1986 Porsche 928s 32v manual trans has a 17 year old Conti iming belt (30k miles on belt) replaced in 2003 stored in southern California garage. I'm not worried because I'm planning on converting it into electric.