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Saturday, 30 September 2017 11:30

Porsche 944 Cam and Balance belt replacement

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.
* Dayco
* Gates
* Bosch
* Continental
 
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)
 
Other advice.
* 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 :)

Tuesday, 08 January 2013 14:38

924, 944, 968 Gear shift issues- Part One

The Porsche 924, 944 and 968 have a lot going for them, good weight distribution (good handling), reliability, interesting styling, pop up headlights (cool!) as well as reasonable power levels which allow them to keep up with much more modern Porsche models.

I own over 20 Porsche cars, including everything from a 1980's Porsche 911 Turbo, through to a modern day Porsche Boxster and yes, a few front engined, watercooled Porsche, in fact, one of each model except a 924S. So I can say, hand on heart that these are fabulous cars, and if you have never driven one, I think you should. Just make sure it is a well sorted one, because there are a few items of wear and tear which can really ruin the experience.

One problem is the condition of the gear linkages, which is what this article is all about, 924, 944 and 968 Gear linkages and how a well sorted one will massively change your driving enjoyment.

Ever driven a new car? A race car? or a well restored car? One of the best things about a fresh new car, or a well restored old one, is the tactile feedback. This is especially true of Porsche cars.

Tactile feedback is how the car communicates with you, how the steering wheel, pedals and gear lever feel as you move them, as well as how they comunicate back to you.

With a gear lever, if all the linkages are in good condition the gear selection will be precise, smooth and comunicative. Lets take a look at all those aspects.

Precision.

A good precise gear shift pattern is something to behold. You could lay a laser cut H pattern plate in place of the leather gear lever gator, and the gear lever will move in a precise predictable pattern, the benefit of which is that you will be able to find gears easily, quickly and without fuss.

A worn out linkage is just the opposite, sloppy and inprecise. So much so, that gears can be harder to find and unless you have had a very precise gear selector mecahnism, you will never realise how bad the current one is.

Smooth.

A tight and precise gear linkage will also be smooth, without binding or changes in resistance as you change gear which can make the assembly seem vague and ultimately will reduce your confidence in driving the car.

Comunicative.

As long as the transmission is in good working order (they nearly always are) a good gear selector assembly will not only be a joy to use, but will be another point of contact giving you feedback from the car.

A good assembly or linkage will move by slight or tiny amounts as you come on and off the power, as well as when the power is in or out of the ideal powerband of the engine, so as your hand is resting on it poised to change up or down a gear, you will feel those tiny movements through your hand, connecting you further with the car. Unfortunately, any wear within the linkage can reduce or completely remove this tactile feedback from the driveline.

Not only this, but a good gear selector will also work to allow you and the transmission to work together. This may sound crazy, but when driving hard with a good gear linkage, the transmission will assist pushing the assembly out of gear as you start to move the gear lever out of gear, as well as pulling the assembly into gear as you enter that gear. The result is that you feel as if you are just guiding the transmission as to what you want to happen, the transmission then picks up on these signals and works with you to bring the car out of one gear, and into the next. You loose all this with a worn linkage. 

So lets take a look at the gear linkage and see an overview of how it is laid out and what components are involved.

 

On the left (in red) you can see the main gear lever, at the right you can see the transmission with the rear linkage in blue and in between you can see the main linkage shaft in yellow.

The main linkage shaft is not a problem and rarely suffers from wear. However the main gear lever (or front shifter as it is known) is prone to wear, as is the rear linkage assembly.

3. Wear in the linkages

With standard parts, even within 20,000 miles or just a couple of years the linkages pivot points begin to wear out. As well as wearing out, they begin to rust, which causes tight spots where the linkage binds up or is stiff to operate.

The main gear lever.

In particular at the front of the car, the main gear lever suffers from the main pin wearing, as you can see in this picture. It often wears into the shape of a barrel as you can see here. The pin in question should be a nice fit into a hole in the end of the main linkage shaft. As soon as the pin wears, that allows the front lever to become a sloppy fit, destroying all feedback and precision. Lets take a closer look.

As you can see, the pin has worn into the shape of a barrel, whereas it should have two parallel sides, this uneven wear is caused by a combination of corrosion (which forms because the part is made from mild steel as well as being exposed to damp conditions) and through general wear of the gear lever applying sideways loads onto the pin when selecting 1st, 2nd, 5th and Reverse gears.

Now lets take a look at a standard used rear linkage.

 

The standard factory rear linkage is made mostly of four materials, mild steel, cast iron, cast plastic and rubber. It also has four main components. In the following gaudy image we have colourised the four main components for the next explanations.

In this image you can see the yellow section. It is manufactured from mild steel. It connects to the main linkage shaft via a single bolt, and it passes through the red item which is made of plastic. The problem with this is that in time water enters the gap between the mild steel and plastic, causes corrosion of the mild steel, which then acts as an abrasive against the plastic, the result is the plastic section worn out and loose, as well as in some cases the yellow item can no longer pivot easily inside the red section. If you look in the previous picture, you will notice an abundance of rust where mild steel meets the cast plastic part.

The blue section is what actually connects to the transmission. It is made from cast iron and does not rust. However it has a mild steel pin, which passes again through the cast plastic part (red in the diagram) and causes wear for all the same reasons as with the previous (yellow) section.

Lastly you have the area coloured in green. This section is known as the cross brace. it is made from pressed mild steel, it rusts, however this is not the problem, the problem is that this part is designed to anchor the whole assembly against the transmission, to project the force applied to the assembly into changing gear, rather than into just moving the whole assembly. However, this section is connected to the transmission and the yellow coloured item by the use of rubber mounts. In time, rubber degrades, splits and can even fall away, completely ruining the quality of the gear shift.

So what to do?

Now that you have a good understanding of how the 924, 944 and 968 gear linkage works, and why it is probably not providing the best driving experience to you, what can be done about the issue?

The first option would be to replace the items with new factory items. Which would typically cost about £30 for the front gear lever, and about £130 for the rear linkage assembly for the parts. However, in time, possibly as soon as 20,000 miles or within 5 years the quality of the gear selection will again degrade.

The only other option would be to replace the parts with further upgraded parts which will not be susceptible to wear, corrosion and maybe offer a better design than the original parts... But that is a topic for the next article in this series,,, 924, 944, 968 Gear shift issues- Part Two

Monday, 30 April 2012 13:38

924, 944 and 968 Servicing and repairs

924, 944 and 968 Servicing tailored to your requirements

With its roots stretching back to the original 924 in the mid 1970's which evolved into the 924 Turbo, Carrera GT and 924 S, the 944 was released in 1982, featuring the new 2.5 Litre engine with a complicated belt arrangement requiring specialist attention. Later a Turbo model was introduced, 16 valve variants and capacities of 2.7 and 3.0 Litre also evolved. Eventually in 1992 the model was replaced with the 968, featuring variocam variable cam timing and a new body design. Each model of 924, 944 and 968 requires its own attention to detail only available from an experienced specialist. If looked after correctly, there is no reason why this model should not last forever and provide the same driving experience as they did when new.

At JMG Porsche we are familiar and equipped to deal with with both the earliest 924, 944 through to the last 968. This includes the 924, 924 Turbo, 924S, 944, 944S, 944S2, 944 Turbo, 968 and 968 Club Sport. We are even experienced with the more unusual 924 Carrera GT, 944 Turbo Cup, 968 Turbo S and 968 Turbo RS.

Selecting the correct service for your Porsche can often be a confusing task for those who do not deal with it every day, more so if you only cover few miles per year, so we tend to recommend that when you need servicing ask us for our advice, we will be more than happy to ask you a few questions and reply with the ideal service for your Porsche.  If on the other hand you are sure which service you would like performing from the factory schedule, we are also more than happy to do so.

As part of the service your car will be inspected beyond the usual items listed by Porsche to be inspected. Should we find any problems, we will try to call you so it is important to make sure you are available by telephone and if you are unable to answer our call, to call us back as soon as possible so we can discuss the issues and if need be, so you can authorise any additional repairs.

We are probably more experienced at maintaining, repairing and modifying these models than anyone else in the UK and possibly the world. Our chief technician and managing director, Jon Mitchell is also the author of books on the subject and the technical advisor to the Porsche 944 registry of the official Porsche Club of Great Britain. Beyond this we have experience of building some of the most powerful 924, 944 and 968 turbo and non turbo Porsche in the UK and possibly the world. In short, we probably know more about these models than Porsche do!

 

Minor service - £199.20*

Major service  - £329.20*

Brake fluid replacement - £59.10

Including all parts and labour

 

Repairs at a reasonable hourly rate of only £79.95 per hour for cars over ten years old

 

Porsche Models over ten years old are considered as classic cars and as such in our ongoing commitment to keeping older Porsche cars on the road, we discount their hourly rate to what you see above.

* Servicing includes all parts and labour except for the cost of additional fluids which are only specified to be topped up in the factory service schedule, such as screen wash, or for additional parts or labour not usually required to complete the service, due to corrosion or other damage.

All prices are plus VAT at the standard UK rate.

 

Interesting service and repair information for the Porsche 924, 944 and 968 models.

Service interval - Even though the service book specifies six monthly and yearly services. We would strongly recommend that all Porsche models are serviced at least yearly or every 10,000 miles if more than 10,000 miles are covered per year to avoid expensive repairs and to potentially catch issues early, where they may be less expensive to repair.

Engine failures - Not as common as you would expect, we at JMG Porsche have never had to replace one of these engines due to wear, however we have had to replace many due to insufficient servicing and maintenance, but there are still worthwhile ways of avoiding unexpected large engine rebuild costs. One of which is proper servicing by a real Porsche specialist, which may not need cost as much as you think. There are also some ways to avoid unexpected bills by following some of our other advice bellow.

Brake fluid - Did you realise this should be changed every two years? Not doing this can cause problems with expensive parts within your car, such as the ABS pump or any part of the brake hydraulics due to water contamination as the brake fluid actually sucks moisture out of the air (hydroscopic), so even if the car is not used, the brake fluid must be changed every two years!

Water Pump - Often thought of as a part which fails with age, mileage and quite suddenly, leaving you stranded, our expert technicians are used to inspecting these during services, and so may spot tell tale signs of failure long before they become an issue, so saving you from the indignity of being broken down at the side of the road. A 944 and 968 Waterpump is also part of the cambelt drive mechanism, so it failing can cause serious damage to the cylinder head and engine as a whole.

RMS - Rear main seal - Something else you might see horror stories on the internet about, these used to be a real problem and Porsche re designed the part several times to arrive at the current design which is the only one we at JMG Porsche use. Like an IMS Bearing replacement, this is best performed during a clutch change, however on tiptronic models or on cars not needing a clutch, they can be changed at any time.

Transmission services - Not clearly noted by Porsche for when the transmission should be serviced and this vital expensive part of your car should not be overlooked. Just like your engine, the transmission is filled with oil/transmission fluid, which over time degrades. Not only this, but not many realise that many Porsche transmissions also contain a filter, which becomes clogged over time and can starve your transmission of lubrication, causing expensive repairs. We recommend all Porsche transmissions are serviced every 4 years or 40,000 miles, whichever comes soonest.

Diagnosis - Long has gone where cars had limited electrical equipment and a wiring diagram could be found in a manual from Halfords. Now the Porsche models have multiple separate computer systems, which all talk via networks, and many sensors to feed those computers with information about the world around it all tied together with many hidden wiring looms of thousands of wires and connectors. This can mean that in the event of your Porsche suffering an electrical issue, it is important that a Porsche specialist auto electrician is available, as we have at JMG Porsche. It is also important to understand that sometimes, finding the fault will not be as simple as plugging in a computer.

Drive Belt - Many of you may have had cars where a drive belt, timing belt or cam belt needs to be changed at a regular interval. Your Porsche model has a belt which should be changed every 4 years. Failure to do so can cause instant overheating, loss of power steering and damage to the engine very suddenly. We recommend you have this changed at least every 4 years.

Cam and Balance belt - The 924S, 944 (ALL) and 968 (ALL) have a cam belt and balance belt, which has to be set to a very precise tension and run across various pulleys, tensioners and rollers to function correctly, if these are not maintained with a new cam belt and balance belt every 4 years, and a new waterpump, tensioners and rollers (as well as front engine oil seals) every 8 years, the consequences can be catastrophic to say the least.

Brakes - The Porsche 944S2, 944 Turbo and all 968 models are fitted with Brembo callipers, which overtime suffer from corrosion build up which can cause the pads to stick and bind up within the callipers or even make it difficult to fit new pads. When this happens the calipers require a service rebuild of the slider plate mechanism, which needs to be performed by a specialist with the right experience, techniques and tools to make the repair more than a very temporary one.

Heavy clutch? - A heavy feeling clutch which is stiff to use is not normal on a Porsche and often a sign that the clutch has almost worn out. Ignoring this can cause further damage, such as to the dual mass flywheel and clutch fork.

Alarm system - At JMG Porsche we are experts of all Porsche security systems and have reverse engineered all the various control units. This not only means we can program new alarm control units and keys to your car, just as the main dealer can, but in some cases we can repair your old alarm control unit and keys, or in some cases recover your old keys to be used on the new alarm control unit, which is a service unique to JMG.

Alarm system causes - In most cases the cause of alarm control unit failure is water damage, we can perform modifications to your Porsche model to help mitigate the chances of this happening to your Porsche.

Monday, 26 March 2012 14:42

Turkey powered 968 Turbo

From a 968 Club Sport poorly converted to turbo power by another specialist, into a JMG 2.8 968 Turbo, a typical JMG Special Projects car.

The Porsche 968 has always been a very capable car, with near 50/50 front to rear weight distribution it handles like a dream, big brembo brakes with upgrade paths allow it to outbrake most cars, and a 3.0 Litre 16 valve engine with variable cam timing, the performance is sharp too.

Porsche made four special 968 Turbo RS models for racing, and a handful of Turbo S models for the road.

With JMG Porsche having close contacts in the Porsche motorsport division in Germany and a level of involvement in 944 Turbo Cup and 968 Turbo RS development, we know exactly what's needed to build a 968 Turbo or Turbo RS, both in the original factory way, but also using the very latest in technology.

When this customer called us for some advice about his 968 Club Sport race car, it quickly became apparent that the customer had another specialist install a 2.5 944 Turbo engine into his race car, which was now smoking heavily. Our advice was simple.. Bring it to us so we can check the engine!

Compression and leakdown tests were performed and a borescope camera was used to examine the inside of the engine without a full stripdown. It became quickly clear that this engine had scored bores.. Running the engine quickly highlighted a knock from the big end bearings.. It was clear that this engine needed a rebuild. We also spotted a multitude of other problems with how the engine had been installed, which did not make us very confident about how well the conversion was performed or how the engine had been built in the first place.

The customer was not impressed, it turned out that this was the third engine the other specialist had supplied! To top it off, he had never been impressed with the performance.

After a long chat with the customer, it became clear what he really wanted was maximum performance, but in the race series he raced in, with a turbo charged engine he had to have an engine with less than 2.9 litre displacement to qualify. This was clearly a candidate for being a JMG Special Projects Division job.

We asked the customer to leave it with us for a couple of days so we could formulate a plan. More importantly we wanted to read the regulations for his race series to see what we could and could not do to his car.

If a diagnosis, modification, repair or build is likely to evolve unto unexpected tasks, research, development, prototyping or, as in this case, may turn into a can of worms, we recommend its worked on as a special projects car, simply because it may be impossible to estimate the duration of the car's stay, what we might find, or what additional work the customer may request. Cars like this can run a mockery of our diary for the usual work of a Porsche specialist, this way the car will be worked on specifically by our top technicians without diary constraints.

A Plan was formulated, a new JMG 2.8 Engine (Rather than the factory 968 Turbo RS 3.0), with a custom programmed engine management chip for the standard 944 Turbo engine management system, a larger hybrid ball bearing turbo, uprated exhaust, bigger injectors, bigger fuel pump and a free flowing air filtration system. We estimated 425 BHP and 500 pounds of torque with full boost being possible as low as 2800 RPM.

The customer authorised the plan, the engine was built, but something was still nagging away at me, why did this car go through so many previous engines?

The old engine was sat in a corner of the workshop looking very sorry for itself, so even though the customer had not authorised a postmortum, he had just wanted us to throw it away, we decided to perform a post mortum anyway.

The engine was filthy, covered in corrosion, but it did have all new gaskets. When we build an engine, we make sure every part is either new, or if re-used it would be cleaned, bead blasted and if needed, replated. This engine was something else, it looked like an old used engine, where someone had used new gaskets, had used gasket sealant where none should be used, had a cracked oil pickup pipe, a multitude of other sins, including the belts were not even set correctly! Even the crank was ground undersize but standard bearings had been used! But the oil pickup was the smoking gun.

Back in the day I had my mentors, one of which used to refer to poorly built engines as "Turkeys", the old engine was the worst "Turkey" I had ever seen!

Now knowing that the previous engine, or engines, had never had a chance of living a long life, we were confident that we could install the nice shiney new 2.8 Turbo engine into the race car.

It fired on the first turn of the key, ran sweetly, was tuned and went off on a car transporter headed for its first venue, the famous raceway of Spa, where it performed faultlessly and put a massive smile on the face of the customer, with performance blowing everything into the weeds.

The moral of this story? JMG Special Projects Division, as with JMG Porsche, know what they are doing, you might save a few pennies going elsewhere, but often you will find that you will just end up having to have all the work done again by an expert.