alordofchaos

Hi, new here but I've been reading lots of great stuff.

Reading about a recent timing belt failure, the lady with over 100k on her original belt, and a recent rant about "why can't the little things work forever" in another forum has got me wondering...

Why are the timing belts in the 944/924s so quick to go?

Is it heat, the way we drive these cars, mechanical stresses on the belt? Bad design? Timing belts on other cars seem to last a lot longer - cars with engines that have more HP, create more heat, etc.

Belt changes every 30k is a good preventative measure - but one you don't see this problem on other cars.

Why isn't there a timing belt for the 944 that will reliably last for, say 50k?

Granted, that's not enough to make me give up my 944

theedge

The belt isnt the problem, the engine is. The block and head is all aluminum, which expands more than iron. This means that as the engine expands, it stretches the belt. Then add to the fact that there is no real autotensioner that keeps the tension constant, and you have a 944/951 timing belt system.

Porsche-O-Phile

I believe they can last plenty long (as evidenced by the 115k mile original belt in the thread you cite), but it's the cheapest insurance you can buy yourself against buying eight (or sixteen) valves at $100+ a crack and possibly a new head, pistons, etc. Compared to that, the couple hundred bucks necessary to buy the tools and parts to do a belt job is nothin'.

Also, I believe the newer belts (Conitech) are of a more modern and durable construction than the ones that were available in 1983, 84, etc. . . Materials have gotten better, belts certainly can last longer, but I ain't rolling the dice on that one.

Porsche-O-Phile

Yea, if the autotensioner actually does what it's supposed to!

Sorry, I can't stand those things. PITA to work on. I'd ditch it in favor of a pulley/roller 10 days out of 10.

Scott at Team Harco

If properly maintained and tensioned the timing belt is scheduled for replacement at 45,000 miles. Is that a lot less than 50,000 miles? According to my quick stop over at Clark's garage - the 968 has a replacement schedule at 60,000 miles.

I don't think it is so much a matter that these belts don't last as long as those in other vehicles - it's more a matter of the cost of repair caused by a failed belt that brings out conservative numbers.

Then again - there are the religious owners who just pray that their belt won't break regardless of how long they let it go.

tifosiman

Silly Catholics. Instead of "pull and pray", that must be "turn(the key) and pray".

Techno Duck

The belt problems are the achilles heal of these cars. Having done it three times now however, the down time is cut to about four hours work start to finish.

xsboost90

the reason for the belt intervals being so short is

1: the belts are skinnier on the 944 than most cars- to cut down on the resistance of the belts AND because it was needed to fit the motor into the car.

2: the close tolerances of the porsche engine make having a tight belts necessary as they dont have the play room that most eco- cars have to slop around. I dont think the expansion of the engine has anything to do w/ it since most hondas etc have alum. engines as well, although i never really did like the self/non auto tensioners we have. My supra had a little hole in the timing cover and when you did a retension, you loosened the bolt in the hole, then tightened it. That reset the tensioner and you didnt have to pull the covers.

alordofchaos

And if you're wrong, you're lookin' at a whole lot of money?

Thanks for the enlightening (and quick) answers, guys.

It's just that every dollar spent on a timing belt is a dollar less on pretty shinys or go-fast goodies. But like y'all say, it's some cheap insurance.

bearone

mumbo jumbo bs.

before the p-car i had a bunch of bosch fi volvos.

volvo's had auto tensioners in '87, belts were good for 50k and extremely easy to change and reliable.

the motor had an aluminum head so the hot/cold, unequal heating as the problem is bogus for 30k belt change.

Serge944

After doing belt changes on several 944s, I wouldn't hesitate to go 45k miles, even on a car mainly used for spirited driving. 30k is overkill, unless your car's cooling system isn't functioning as well as it should.

Then again, I don't even use any kind of tensioning tools - so take my advice with a grain of salt.

KuHL 951

If the expansion coefficients are the problem here then why do most other all aluminum engines have up to a 100K belt? The BMW belts from the same era are 60K, the Honda/Acuras are 75K, Toyota 100K, again all aluminum. In addition, if the 87+ 944 has an auto tensioner then why wouldn't the interval be longer than a manually tensioned belt? Is Porsche being much too conservative or just trying to increase maintenance revenues? I suspect the answer is the nature of the valve train on the 8V motor. Without a means to adjust cam/valve clearance they must have built them to a closer tolerance but it still should have no effect on belt life with a good autotensioner.

I think it's all a bunch of hooey thrown in with a good dose of Duetch Marks.

Mighty Shilling

I want a 968 autotensioner in my 924S... I wish it was easy/econmical to retrofit one on there... mmmmmm....hydraulic belt tensioner.... :drool:

951Tom

I'm due for a belt change also and I think I will try Goodyear belts. It seems they may have a designed a better belt. They also list the balance shaft belt.

http://www.goodyearbeltsandhose.com/cars/pdcam.html

Tom
'87 951
'86.5 Supra
'00 Jeep Cherokee Sport

Zen dude

How many people have broke a belt before the 45000 mile or 5 year period?