Timing Belt Breakage - Why?

[soloracer]

Here is the situation:

The timing belt on my 944 Turbo broke - possibly damaging the exhaust valves. The timing belt was just replaced approx. 1000 miles ago. I call the shop, because I am sure it should be a warranty fix, and get told "We will take a look and let you know" The entire engine was rebuilt approx. 10000 miles ago by the same shop.

My question is how could it not be covered if there is a parts and labor warranty by a reputable shop? What would cause the belt to break that would NOT be covered? If something seized (bearing, etc.) or a part failed that should be covered right? They told me that over revving would do it however I was in my underground parkade driving towards the automatic door at about 10 mph when it went. I know that it was not over revved and have never heard of this before. Besides, don't our cars have a rev limiter?

I would like some feedback as to what you think could cause such breakage. Thanks.

[TSNAPCRACKLEPOP]

first, i would read your paid reciept, both sides, for the shop policy. if they regularly do 944 cars, they know about the problem. find out which belt is on the car, a good one or a cheap one? i would get a pix of it before they "loso" it. also, ask to see their porsche tensioning tool.

[carsontc]

exactly what parts were replaced approx 1000 miles ago and what was the date?

and why was the the timing belt replaced after the entire engine was rebuilt only 10,000 miles ago?

[soloracer]

There have been numerous problems with this engine since the rebuild - including a previous timing belt breakage which left me stranded beside a highway. The latest problem was with the sleeve in the block that the oil pressure release valve sits. The sleeve moved, blocking the valve and causing high oil pressure and the oil filter to blow. I was told that there was oil on the old (if you call a belt with minimal mileage on it to begin with old) belt and that a new one was needed. I believe the invoice included the belt, bearings and rollers.

The date of timing belt replacement would be about 3-4 weeks ago.

[Dantilla]

Possibly a faulty belt. If so, the manufacturer of the belt may have some liability, but doubtful. They would probably just replace the belt.

The other possibility is incorrect tension. With the belt gone, this would be difficult to prove.

One other thing to look at is if all the pulleys are lined up correctly or not. If one pulley is offset, that would dramatically shorten the life of the belt.

[Scott R]

What year is your turbo? I looked at a turbo that had lost several belts in a very shot period of time. It turned out the the belt roller on the auto tensioner was on backwards. Its a common mistake but the belt works its was to the back cover and chews itself up.

[AFJuvat]

Originally posted by soloracer
The timing belt on my 944 Turbo broke - possibly damaging the exhaust valves. The timing belt was just replaced approx. 1000 miles ago. I call the shop, because I am sure it should be a warranty fix, and get told "We will take a look and let you know" The entire engine was rebuilt approx. 10000 miles ago by the same shop.

Have you followed the published maintenance schedule?

Belt replaced
Retension at 1000 miles
retension again at 15000 miles
replace at 30k miles

My question is how could it not be covered if there is a parts and labor warranty by a reputable shop?

Two excellent reasons why it would not be covered:

Belt not tensioned according to maintenance schedule.
Shop is unable to control HOW the vehicle was driven since belt replacement and before tension (it is not recommended to exceed 5500 - 6000RPM until first retension)

What would cause the belt to break that would NOT be covered?

See above.

Also, oil saturation of the belt will cause premature failure.

In the event of oil contamination, the shop cannot be responsible for it if it happened after the belt was changed. If oil contamination was there when the belt was changed and not repaired, it would depend on if you were advised of the leak and declined to fix it.

If something seized (bearing, etc.) or a part failed that should be covered right?

Only if they replaced it as part of the belt change. Shop cannot be held responsible if your roller siezes 500 miles after it leaves the shop. Now, if they replaced rollers and one of them were defective, that is a completely different story.

They told me that over revving would do it however I was in my underground parkade driving towards the automatic door at about 10 mph when it went. I know that it was not over revved and have never heard of this before. Besides, don't our cars have a rev limiter?

From the shops point of view, you may not have been over revving it when it broke, but how about any time between the time you picked it up and the time it broke? Can you prove it? It is a sad fact of life that a shop just cannot "take your word" on testemony like that.

Yes, there is a rev limiter - around 6500 RPM or so - see earlier comments regarding not exceeding 5500 - 6000 RPM until first tension.

AFJuvat

[BlueQuestTSi]

So, newbie-ism at it's best here..... Even you guys with the new fangled fancy shmancy self adjusting timing belt tensioners still have to have your belts 're-tensioned'?


Makes you wonder what the self adjuster is doing during the 'off hours'.

And to think, after reading Perry951's story and how he added an upgraded belt tensioner to the older engine block he received, I thought it would be a cool upgrade to do myself....

[AFJuvat]

Well, withthe auto tensioner - it is more of an inspection than a retension - making sure it falls withing the range etc.

Do have them check the tensioner pulley for proper orientation

AFJuvat

[Scott R]

It's just not a highly accurate device, I replaced the original auto tensioner on my 87 when it was no longer reading correctly against the 9201. Its just a spring actuated arm, the spring wears out over time just like anything else.

[ae1969]

I'll tell you this soloracer............

When they take it apart to look...........

YOU BE THERE. Take a good look at everything.

I used to have my 944 serviced at the local shops for about 9 years before I started tinkering on it myself.

The first time I went to change the belt (myself). The previous mechanics put the WRONG rollers on.

There are not many 944's left in alberta and frankly not many mechanics left that know these cars. I only trust one mechanic in all of edmonton and I have had my car serviced at every single porsche shop in town!



Good luck..... but unfortunately I think you are going to get the short end of the stick on this one.

[carsontc]

Originally posted by soloracer
There have been numerous problems with this engine since the rebuild - including a previous timing belt breakage which left me stranded beside a highway....I believe the invoice included the belt, bearings and rollers....The date of timing belt replacement would be about 3-4 weeks ago.

I'm with Alex on this one...good luck

[SoCal Driver]

The tensioner toothed roller for the timing belt has to have it's single guide flange toward the engine.

The tensioner for the balance shafts belt has it's singe guide flange away from the engine.

Be there on the tear down and check these rollers first thing.

If the belt seperated cleanly then it was too tight.

If there are teeth stripped from the belt then it was too loose.

Note: You can tension the heck out of these belts and they will last at least 15,000 miles. You may have some binding in the cam or the water pump may be going bad and siezing. Back of the timing belt will be scuffed clean where the markings are almost gone.

[924Sman]

Over reving is meant in down shifting not hitting the limiter! If you down shift the car to a gear with out raising the revs to match you are going to blow the belt. Example...in 4th gear doing 80 and down shift to second suddenly or in error will over rev the engine and usually go PING!!! Make sense?! Many encounter this problem by using the gears to slow the car down instead of braking to the proper RPM, blip the throttle and down shift. And if they misshift or don't get the RPM's up for the gear that's where the failure occurs.PS....I forgot to add this part.....! Hitting the rev limiter is when you are upshifting and run the revs too high before the shift. If the limit is 6200 rpm and you throttle past that it will shut the engine down for a second till you get off the gas below the allowed rpm. It is there to keep one from blowing the motor. Sman

[SoCal Driver]

Didn't think there was that much inertia in the cam assembly to over stress a properly maintained timing belt. I could see a problem with heavy duty valve srings and a higher/quicker rise cam.

Back to the FEA!