Porsche 944 timing belt system
Porsche 944 timing belt system
(OP)
I've recently purchased one of these cars, an '84 normally aspirated model. These engines are famous for eating their valves when the belt breaks/slips/feels like it. Searching on-line I've found instances where qualified techs installed a new belt and idlers (all the bearings and belts are sold as a kit) and the engine ate the valves as little as 9,000 miles later, at idle, in the owner's driveway. It happens so often that the most common mod to these cars is to install a Chevy V8.
Do any of you in the industry have any insight as to the problems with this system? I see nothing unusual about the system, if anything it seems to have lots of wrap on the pulleys and good support along its runs.
Porsche subsequently went to chain drives on the turbo models of this engine, and they seem to have their own set of problems.
Do any of you in the industry have any insight as to the problems with this system? I see nothing unusual about the system, if anything it seems to have lots of wrap on the pulleys and good support along its runs.
Porsche subsequently went to chain drives on the turbo models of this engine, and they seem to have their own set of problems.





RE: Porsche 944 timing belt system
I wonder if the Porsche belts might live (and die) in a hotter engine bay?
RE: Porsche 944 timing belt system
The belt on my car doesn't look much smaller than that on much bigger engines, so I suspect different manufacturers stress their belts to a different extent. Belts are available in various grades (three from Gates).
So between all that lot, you shrugs and read other people's experience.
Cheers
Greg Locock
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RE: Porsche 944 timing belt system
This engine has NO tolerance, in fact I am shocked at how thoroughly a job the pistons do on the valves -- double bends in the stems. Not cheap to repair!
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Second was on our 83 Turbocoupe. As it turns out, the valves cannot reach the pistons on this Ford engine so no problem, just replace the belt taking care to line up all the pulleys, oil pump drive, dizzy, etc.
One other comment on reliability of the belt...When I rebuilt the 2.3 Turbocoupe engine to much higher hp (295 @ the wheels on the dyno) I chose the Goodyear belt recommended by JBA and changed it at 50k miles and it was still in the car at 100k miles when I sold it.
The last few cars I have purchased don't use belts...I just don't need the added aggravation at this point.
Rod
RE: Porsche 944 timing belt system
I'm surprised Porsche couldn't get these to live. The devil is in the details.
RE: Porsche 944 timing belt system
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Porsche 944 timing belt system
It just ain't rocket science, I would have expected more from Porsche.
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Even with minimal tensioning it will reduce the belt orbiting or avoid it coming in resonance.
RE: Porsche 944 timing belt system
They later went to a spring tensioner, then to a hydraulic one, but there is little improvement in belt endurance. Bottom line? They did not properly engineer the one system that needs to be bulletproof on an interference engine.
RE: Porsche 944 timing belt system
I just only noticed the picture with your first post.
The TB idler pulley prevents the belt to go orbiting but doesn't prevent it to deflect inwards.
The traction side of the belt goes straight from the crank pulley to the camshaft pulley. This is not the case in for example most of the DOHC engines.
If the idler pulley forces the belt to make an inward bend it will probably hold it better seated against the pulley. Unfortunately there seems to be very few place here for such a construction.
Is it possible to start the engine without the belt cover (or with one with a window) and film the belt with a high speed camera?
RE: Porsche 944 timing belt system
The original design had only static tensioners, so when the belt is properly set for running conditions, it is noticeably looser when the engine is cold (all aluminum engine). Many of the failures are idling in the driveway on initial start-up.
As you note, the tension run is long and largely unsupported. It also passes close by the opposing run, and at idle, I'm betting the long run flops around enough to actually touch the other run (cog to cog).
So what the engineers at Porsche did, in 3 distinct steps, was this: They added a guard rail, a smooth sheet of stainless, between the two runs at their closest approach. Then they replaced the static tensioner pulley with a spring-loaded one. Apparently that was also unsatisfactory, so they later made it a hydraulically-actuated (oil pressure) tensioner. (I said in my OP that they later went to a chain, that is incorrect)
The shield prevents contact, the active tensioners addressed the cold-to-hot variations.
What's also interesting is that this engine is half of the 928's V8, and the V8 models apparently were not prone to belt issues (because the two runs never approached each other closely?)
I found the maintenance records on my 944, which has 97,000 miles on it. It's on its 4th set of belts and tension rollers. The bill at each replacement was over $1,000 (parts and labor).
RE: Porsche 944 timing belt system
thnx, jack vines
RE: Porsche 944 timing belt system
I finished the water pump upgrade a week ago, with new belts, idlers, and tensioners. I tensioned the belts using my thumb and index finger, 90-degree twist method. I am about ready to open it up for the re-check after initial run, but no problems so far. The balance belt is quiet.
There really are no aftermarket belts, all are either Conti or Gates (OEM).
It's hard for me to accept that an '84 model is a 25-yr-old car, an antique in most states!
RE: Porsche 944 timing belt system
My wife's "new Lincoln" is the same age as MY first car, a '49 Mercury---and---at the time, I thought it was positively ancient, a vintage classic !!!
How time flies AND how much my attitude has changed.
Rod
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Rod
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Pretty good 1st post in the forum, I'd say.
It was never ok, in my shop, to change a belt or chain without taking the time to double ck the timing...An easy step that should always be done. Many engines that have separate drives for balance shafts, dist drives, oil pump drives can very easily get 'out of sinc' and cause monster problems, even if the camshaft timing is correct.
I have made no secret of my disdain for 'belt drives' in the past and nothing has happened in the last few years to change my mind. I used belts on the cam drives of a couple Ford/Cosworth based race engines that worked well enough---with constant maintenance! For a street car, it's a shortcut in mfgring that I could do without...I won't buy a car with a belt.
Rod
RE: Porsche 944 timing belt system
I did my belts and the water pump upgrade, and haven't had any problems so far. Well, just the normal Bosch problems...
RE: Porsche 944 timing belt system
You said, "Porsche recommends that after you pay a mechanic maybe 4 -6 hours labor to put the belts in (simplest scenario, even more for a water pump job), you are supposed to drive it a couple of weeks and then pay him to essentially re-do the job, "just to be sure"?! Name another car where this is called for..."
As always, your car, your money your decision. However, raceu gives it straight and true. I've known 944s and their owners since the car was new. Some are made for each other; some are not. My suggestion, based upon many years of observation - Cut your losses, sell the 944 now. I can opine from your posts you are most likely never going to be happy with the car.
thnx, jack vines
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
No worse feeling than the realization that you have just thrown good money down the drain...unless it's the knowledge that you are STILL doing it!
Rod
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Hope you make it ok. Seems like a lot of members are loosing their jobs...That sucks, I know...BTDT!
Rod
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
http://www.canam50minirace.com/Entrylist.html
http://forum.moasf.com/index.php?topic=2875.0
If your in the neighborhood...Also we are taking the Lotus Cortina out to Willow Springs in April 4th/5th VARA race for my son to drive his first race.
http://www.vararacing.com/
Rod
RE: Porsche 944 timing belt system
When the belts are replaced on a 944, it must have the tension checked 1500 miles later. The new belts stretch out a lot. Its a quick simple procedure, I think shop time is specced at 1 hour if that for an 944NA. The plastic belt covers are removed and the tension should be checked with the tools designed for the job.... Not the hokey finger twist method. If it doesnt get checked on schedule then the belt gets too loose and damage can happen. No reason to sell it, as long as you follow the proper maintenance schedules and procedures for doing the belts.
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
My point was the OP has a unresolvable conflict between what is now a very cheap car to buy, but a very expensive car to maintain. My experience is OP will let the maintenance costs obscure the unique virtues of the 944 and resent more than enjoy the ride. As Willy Nelson titled one of his earlier songs, "She's Not For You."
thnx, jack vines
RE: Porsche 944 timing belt system
http:/
No surprises there...
Jack, my original post was questioning how Porsche, a preeminent engineering house, botched what is a basic system mastered by every 3rd tier auto manufacturer. It has kind of devolved into a rant or whining session, my apologies for that. I actually find the costs of parts to be more or less stuck in the '80's, a 5-yr-old Camry would cost more to repair, part-for-part.
RE: Porsche 944 timing belt system
Regards
Pat
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RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
RE: Porsche 944 timing belt system
Hang in there, I did not start preparing for retirement until I was 50. I planned to retire at 65, but things worked out so well that I retired at 58...Best thing I ever did.
I've kept up with my old portfolio...if I had stayed in the market, I would have lost >60% !!!!!!!!!!! I'd probably be one of those "greeters", the old geezers, at Wall*Mart ;o(
Rod
RE: Porsche 944 timing belt system