Andy Kay

Roger,

Sean did the TB/WP/PK Tensioner on 09/15/12 @ 90k. Today, 16 months later, I'm at 120k. Almost all Highway driving - no track time. The 60k interval (150k) would be a little over 3 years. When do you suggest the next belt change and would I benefit from using the Racing belt?

Thanks ...

Hilton

Jason,

First ,go to a competent shop, and not the one you've been using.

Second, get them to inspect the tensioner - there's an important washer which is easily mislaid while doing the timing belt job and if its left out then you can get intermittent belt warnings. Its also possible there's an intermittent electrical connection issue elsewhere in the warning system - but that washer would be my first guess.

Bilal928S4

Make sure they put oil in the tensioner.

Jascd

thank you for all the suggestions, some extra info- they put in a new laso pump and rollers with the new belt, the tensioner oil was topped up but the tensioner was not rebuilt (it was rebuilt at the last change, 25,000Km ago). I had never had a toothed belt warning before the TB and WP was done. The car is stock and in good condition with 92,000km on it. The shop where I had the work done is the local non-dealer shop and they service most 928s in the area.

Hilton, can that washer get lost if they did not dis-assemble the tensioner?

Hilton

Yes, its not screwed down, just held there by pressure from the arm which holds the rollers. Depending on the shop, if they removed that arm to replace the main roller or the idler roller, they might have pulled the nose out of the tensioner (to add a small bit of clearance) and dropped the washer.

Other possible reasons for a belt warning include missing/worn bushings on the roller arm, failing water pump etc. It could also be the belt (no manufacturing process is 100% reliable) - but this would be the first report of a failing racing belt.

Either way, having them crank up the belt tension is more likely to cause new failures than fix whatever has failed so far.

dr bob

I've discovered that 'not rebuilding the tensioner' risks erratic belt warnings. First, there's supposed to be oil in the tensioner to dampen the piston movement. There's a rubber boot on the piston end that keeps the oil from splashing out. Rebuilding the tensioner means pop the piston out, replace the o-ring on the piston. New boot and clip/ring, plus the strap/clamp around the outside of the boot. New mounting face gasket, and fill with thick oil or STP after installation. The top boots seem to deteriorate faster than I do belt replacement. They get crispy with time and heat exposure, crack and won't hold the oil any more. Filling with the thicker oil is time-consuming and can be messy. I'm guessing that your mechanic decided to just leave it alone. Or he took it apart, decided it was too much work, and put it back in. Regardless, failing to take this small step in the big process does cause problems. The fluttering belt will trip the warning system, particularly on hard acceleration but also on trailing throttle from higher RPM's. Fluttering belt is also more likely to jump teeth, and it can cause faster wear on cam gears.

When they pull the covers to check the belt tension, peek down at the boot on the tensioner. If it isn't flexible, no leaks, with oil in the tensioner, it needs to be sealed and filled.

Tightening the belt excessively can mask the warning light for a while, but risks WP bearing stress and failure, driver side cam snout breakage, and gear wear on the various cogs the belt fits over.

GregBBRD

One of my issues with running the Gates racing belt is tension and the lack of a specification.

Porsche did all the research on the stock belt and determined the cold tension to be 5.0....that's with a belt that does stretch a bit. Let's also not forget that the engine "grows" a lot between hot and cold. The correct hot tension, with the "expanded engine" was determined by Porsche.....and they came up with a "cold tension".

Since the racing belt doesn't stretch as much as the stock belt....Isn't it going to end up a whole bunch tighter than the stock belt, as the engine expands?

I didn't feel like doing the R&D on my dime....but I figured that someone would also see this problem and figure out the proper "cold tension" to get the proper "hot tension."

For the OP....many intermittent "belt light" issues are from the tensioner not having any oil in it. Have this checked....when you figure out how tight the racing belt needs to be.

WallyP

Some interesting questions...

The tension is set cold, and the bimetallic Belleville washers are supposed to relax enough to maintain that tension when the engine grows. Without thinking about it much, I can't see any reason that the temp correction for the tension should be different for the stronger belt - but I have been known to be wrong a few times.

As Greg says, the lack of oil can cause tension warnings, as can poor electrical contact at three or four places in the system.

ROG100

Gates Engineers where very specific in there answer to the tension setting for the racing belt - "exactly the same as the stock belt". The RTB is stronger and meant to last longer.
I know of at least ten manufacturers of the stock TB and I am certain that the amount of "stretch" does differ between them all - Gates v Continental is a good example.

GregBBRD

Good point. Maybe the Belleville washers will take care of it.

Randy V

I thought the 'Racing' belt used Kevlar cord?

Jascd

Seems to be different schools of thought about the gates racing belt but having read all the posts including the replies to my post I am leaning towards keeping the gates belt (I did think about replacing it with the OEM) and replacing the stock tensioner with the PK tensioner that way I won't (unless wiser heads advise) need to worry about over tightening when the engine heats or a loose belt when cold or flapping at any temp.

MainePorsche

This is the kind of thread that needs to get a bump every once in a while.
Is timely in light of some of the last posts in the 'Cheap Water Pump' thread.
Also, any new experiences/findings from the Wise on Gates Racing v. Gates Stock belts ?