oups59

I was reading my warranty and maintenance booklet trying to find the timing belt required maintenance suggested by Porsche but did not find anything except to check to condition and tension at 48,000 km. Nothing mentioned at 96,000 km.

Is there a official Porsche bulletin specifying the normal change interval for the timing belt?

oups59

I just find this tech. bulletin

GregBBRD

Stock belt, stock tensioner (rebuilt), new gears, factory water pump = 60,000 miles. Check and correct belt tension after 2,000 miles and every 15,000 miles.

Stock belt, stock tensioner (rebuilt), old gears (cam gears still have coating), factory water pump = 45,000 miles. Check and correct belt tension after 2,000 miles and every 15,000 miles.

Stock belt, stock tesnioner (rebuilt), old gears (with coating slightly worn through), factory water pump = 30,000 miles. Check and correct belt tension after 2,000 miles and every 10,000 miles.

Any of the above, with Laso water pump = Laso pump not likely to last 30,000 miles. (I tell people to expect 6,000 to 30,000 miles. Regardless of age or mileage, I will not warranty the labor.....been "burned" too many times.)

Aftermarket belts, aftermarket tensioners, badly worn cam gears = It's a crap shoot. Requires very frequent inspection.

100% truthful statement:

I redo (start over) more "low mileage" timing belt/water pump repairs than I ever do when the mileage limits have been reached, because of improper workmanship.

slate blue

Greg is there a time issue also, some cars have low mileage but more than 10 years have elapsed. Thanks in advance

Jason89s4

^^^^ I too am interested in Greg's and other's opinions on this. The more I work with 928's the more I am of the camp that they 'like to be driven, not stored." While this can be true with all makes of cars, I'm surprised at how many low mileage 928's need significant repairs, as compared to other makes I've restored. There certainly can be unique factors such as poor pre-storage preparation and the complexity of systems, but also due to --don't shoot-- poor design.
Jason

dr bob

Porsche shares no official time-based guidance for belt replacement.

The colloquial wizzdumb here has been six to maybe seven years change intervals regardless of mileage. While Porsche doesn't list a time element, other manufacturers with cam belts do. For example, Honda has used six years until lately when they added a maintenance minder to tell you when and what to do. Prior to that, 105k miles or six years was the guidance on the V6.

A couple folks here have shared that they had failures of their low-miles but long-interval belts.


Fred R mentioned separately that he can't pass inspection in the middle east with tires more than four years old. His climate is a lot hotter and harsher than most in the US see, but it does point to the need for some life expectancy de-rate in hotter places. In Fred's case, the tire life is about half of what we consider in the US. If I lived in a hot part of Arizona or similar, I'd be adjusting my belt maintenance schedule a bit.

FredR

My timing belt is history at 6 years. Excessive heat and the 928 do not mix well. I know from my professional background that rubber and being static do not mix well. Rubber likes to be flexed to keep it rubbery- the reason it is rubbery is because the molecules flex over but just like human joints if they are not flexed they seize up and then when you do try to use them they crack- not as in split but at a molecular level. Heat accelerates this attrition.

In the days when our local Porsche club was fully functioning and we had our autocross events we saw a distinct pattern of natural attrition wherein on a 60 second lap every year of exposure caused a loss of one second of lap time consistently and mileage had absolutely nothing to do with it- after 4 years they were more like bars of soap. Interestingly the latest generation of tyres seem to be doing a bit better but the authorities have not seen that [yet]. Thus a couple of years ago having seen many serious accidents caused by folks ding silly speeds with knackered rubber they said enough is enough and legislated based on the manufactured date stamp, not when the rubber was fitted which invariably is about a year old over here. I was aware of this long before the authorities and always insisted on freshly made rubber or large discounts for older [well kept] stock. Now the local tyre dealers have refused to stock specialist sizes and will only order them upon request - hit a brick or something and you might be out of luck for months!

When I remove my timing belt I inspect it carefully and to date have never seen any signs of anything untoward developing but I am not prepared to risk a belt rupturing. I generally reckon on two belts to one pump- I have had two pump failures- both after about 8 years of service - one was a rebuilt item one an original item and interestingly both did about 50k miles and both lasted similar lengths of time. At the moment I am on a Laso pump and have a spare OEM item with low miles on it as a standby. Thus ironically my belts seem to do better than the pumps [both had impeller migrations but seemingly perfect bearings].

HVAC actuator diaphragms do not do too well and neither do auxiliary belts so they get changed out roughly every 3 years or so and then I keep them as back ups if they look in good nick. If I were back in the UK I would have no hesitation using the belts for 10 years or 50k miles whatever came first. Checking belt tension every 15k miles or three years is sensible, over here I check tension every other year and would adjust if necessary but I do not perceive much in the way of stretch taking place. In 20 years of 928 ownership I have had two alarms in the days when I relied on the dealer doing such and non since I started doing maintenance myself. After doing belt work I run the car for over three minutes to ensure the alarm does not come on and when that is OK I undo the alarm cable and run the car for three minutes to test that the alarm comes on!

GregBBRD

Varies greatly with where and how the car is stored.

I left in a 20 year old belt, for a lady that was just trying to sell diseased husband's car (who had zero money to spend.) The car was super low mileage and the belt still looked and felt like new. I could not find any visual or mecanical reason to change the belt.

I told her to tell the new owner to have the belt changed....sooner than later.

Keep in mind that I've had a grand total of two cars come in with an actual broken cam belt, out of the thousands of 928's I've worked on, for the past 40 years.

And that I've completely started over 100's of "cam belt jobs" (and fixed dozens of engines) from terribly done cam belt jobs.

Sometimes doing nothing is better than doing it wrong....

Wisconsin Joe

And another data point (two actually):

I did the cam seals in my 928 3 winters ago. Belt had approx 17k on it, was 8 years old. It looked and felt fine. I replaced it because a new one was cheap and there was no way I was putting the old one back on.

I did my timing & balance shaft belts in my 944 last winter. Not sure when they were last done, but I've had it for about 22k miles and 13 years. Yes, it was a bit long. Both belts seemed fine. No cracks or splits, some wear, but not excessive.

Edit to add:
As my name indicates, I live in Wisconsin. Cooler climate, not terribly hot & dry like the desert. That tends to extend the life of the 'rubber bits' a decent amount.