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This is not going to be an article about how to change your cam and balance belt on a Porsche 944 or 968, this subject has been covered elsewhere on the internet and personally, it is one of those jobs where if you have not been trained to do it, are not experienced in doing it, you should not do it.. An apprentice at JMG Porsche is not allowed to change a 944/968 cam or balance belt until they have their basic first two years of training under their belt, after that they are supervised on the first few and on probation for the first 4 years with them being checked... So in short, get a pro to do it, ideally a specialist with in depth knowledge of the 944 and 968 engines.
Over the years I have often been asked how often they should change their cam and balance belt on their 924S, 944 or 968, and my answer is "Every 4 years" and change the water pump, front engine oil seals, belt tensioners and rollers every 8 years!
The following questions and answers are here to explain why I advise what I advise and is actually a cut and paste from a recent answer by myself as a technical advisor to the Porsche Club of Great Britain, as a response to a question on their forum.
To an extent, the same advice applies to any belt, on any car, so a Boxster, Cayman or Cayenne/Macan/Panamera or 911 (996, 997, 981 or even air cooled cars) which as a whole do not have cam belts, but do have auxiliary drive belts which if they fail will at best leave you stranded, but at worst can damage the engine or even the bodywork of the car (belts at high speeds make a mess!)
Other than not having a balance belt, the Porsche 928 advice would be the same advice as for the 924S, 944 and 968 owners.
What destroys a belt?
From education training and experience
* Entropy (Everything wants to return to its original component materials) - Very slow
* Oxygen (Oxidises the rubber from the outside inwards, forming cracks eventually, which then allow more oxygen deeper into the belt)
* Wear (Accelerated if the tension is too high or too low)
* Incorrect installation
Who makes the belts for Porsche?
Over the years I have seen the following belts in Genuine Porsche boxes.
How long can an incorrectly setup or installed belt last?
* As little as a few seconds
* As long as a correctly installed belt
Depends on how incorrectly it has been installed or setup (I have seen many weird things going on in 944 belt covers)
What else accelerates belt degradation?
* Contamination from oil
* Contamination from power steering fluid
* Contamination from coolant
* Contamination from dirt/grit
* Contamination from fuel
* Contamination from plastic dressings
* Contamination from sprays such as WD40
* Ionisation of the air in the cam belt cover
How soon can a correctly tensioned good quality belt without contamination last?
* Soonest I have seen is 5 years with a missing ionisation cap.
* Soonest I have seen with no visible signs of cause - 6 years
* Oldest belt that I have seen break was 26 years old!!!
When would I change the belts on my own 944 fleet?
* Every 5 years without fail and I check inside the cover every year for contamination or issues and always check for leaks every time I drive them.
When would I recommend customers change them?
* Every 4 years (as you might not have your belt, oil seals and leaks checked so often as I do)
How much damage is caused by not changing them?
* Wrecked cylinder head (Valve contacts and bent/detaching valve heads)
* Wrecked pistons (Valve contact, sometimes with valve heads detaching and bouncing around!)
* Wrecked cylinder block (mushroomed out pistons split the bore)
* Change the water pump, tensioners, rollers and front engine oil seals on every second belt change. The water pump can fail through age as well as mileage, as can the seals and tensioners/rollers. Any of these parts can cause the belt to fail.
* Make sure your car has an ionisation cap between the distributor cap and upper front cam belt cover.
This is an important one.
When the 944 was designed, it had a hose that ran between the cam belt cover and air box.. This was to bring fresh air through the belt covers, and remove air which had been ionised by the electrical activity within the distributor cap. There was also a plastic cap between the distributor cap and the cam belt cover, to reduce the amount of contamination of the air within the belt cover with air ionised within the distributor cap.
In about 1988, Porsche eventually go to the bottom of why so many 944s suffered with hydrolocked engines following driving through deep puddles or crossing a river/ford crossing... It turned out that as soon as water was sprayed around the front crank pulley, or the pulley entered water, the water would go into the belt cover and the balance belt would throw this water directly at the vent port which had the hose to the air box.. Once the air box contained a certain amount of water, or you turned a corner, the water would flow through the airflow meter, and get sucked into the engine... Nasty.
Porsche then issued a TSB to say that all Porsche models should have this hose where fitted (important) and a blanking plug fitted (Not so important, I leave them open for ventilation on the advice of my mentor at Porsche).
The problem with this deleted hose, is that without it, it is even more critical to have the ionisation cap installed. They are cheap and available.
That is all :)