DKWalser

I guess I know how to kill a thread...

Wisconsin Joe

"Faith in Porsche Engineers".

Sure.

Ask all the 996 owners whose engines suffered IMS bearing failure.

Ask all the Cayenne owners who had plastic coolant pipes fail.

Ask all the Cayenne & Panamara owners who had the bolts on the Vario-Cam fail.

Ask all the Cayenne owners who had the transfer case fail.

The 968 (descendant of the 924 & 944) ended up with a hydraulic tensioner.

The 928 should have had the same, but by the late 80s, Porsche saw the writing on the wall and knew it wasn't going to put much more money into improvements.

GregBBRD

Are you serious?

You think that the 1992 engine redesign to 5.4 liters, with the new crankcase, new crankshaft, new connecting rods, new pistons, new cams, different intake manifold, was cheap compared to a new tensioner????

Not hardly. The reason Porsche didn't change it was simple....it was/still is absolutely fail proof! I'm betting Porsche never had a warranty claim because of a failed tensioner.....it would liiterally have to fall off the engine to fail!

James Bailey

While the stock Porsche tensioner is " fail proof " it is NOT fool proof !! When I sold t-belts to customers who were planning on having their local import shop do the install I would suggest that they ask if the shop had the 928 workshop manuals AND ask to SEE the 9201 tensioning tool BEFORE they let that shop touch their 928 !!
And the tensioner has always been the scapegoat for all kinds of foolish mistakes...... the failure was not the shops fault so obviously no warranty !!!!

GregBBRD

Absolutely true! There are plenty of fools, out there, working on these cars!

I "redo" more timing belt "area" jobs than I start due to mileage (or age.) In the almost 40 years I've been working on these cars, this has always been true!

One does need to use a "decent" water pump (factory new), a decent timing belt (factory or Gates), reseal the tensioner (keeping the spring washers in the proper configuration), and make sure the rollers and bushings are in perfect condition. Some pieces need to have the proper grease applied and the tensioner needs to be filled with the proper oil. And then the timing belt needs to be properly tensioned.

It's not brain surgery....there is plenty of information out there to do it correctly.

And if one does do it correctly, everything will work perfectly for 45,000-60,000 miles, with only a re-tension of the cam belt every 15,000 miles needed.

If one starts with a cheap aftermarket water pump or a cheap aftermarket timing belt, or a poorly designed aftermarket tensioner....they can plan on being back in the belt area every 2,000 to 10,000 miles. This stuff should come with that guarantee written right on the box!

People complain that a factory water pump or a factory timing belt are too expensive. However, after you've replaced the water pump the second or third time in 10,000 to 30,000 miles....the factory part looks like a bargain!

And when the aftermarket water pump, aftermarket belt, or aftermarket tensioner fail and the valves hit the pistons.....you could have bought an entire pallet full of the stock parts.

This Forum is filled with horror stories of water pumps, belts, and aftermarket tensioners. There are literally hundreds of pages filled about these failures and associated problems. Heck, there's four concurrent threads threads about failure, right now!!!!! Tens of thousands of dollars of these pieces been tossed into trash cans, along with tens of thousands of dollars worth of labor, along with tens of thousands of dollars of collateral damage to engines caused by these pieces.

Find me a thread where a factory pump, a factory belt, and a factory tensioner (all working together) have prematurely failed....

Exactly..........there are none.

PorKen

The stock tensioner was design to be 'fail proof' for 15,000 miles. (Wow! ) Then it's back to the dealer for a look-see. (Going by the tiny bearings and the use of plastic bushings, you can see why frequent maintenance is a must.)

The stock tensioner has no capability to extend to take up any extra belt, EG. when the engine is cold or at high rpm, so belt tension is set quite high to pre-stretch the belt. (But it still flaps - take off the center cover and check it out for yourself.) It barely has any flex, if at all (see here), and only when cold. Any damping is likewise only possible when cold.

The stock tensioner should have only been used, optimistically, on the non-interference 16V engines. Instead of designing a proper system (a la 968) for the extra load of two more cams (more load = more belt stretch), Porsche instead stuck on a band-aid, a low-tension light, knowing it likely would not make it to even 15,000 miles. Instead, it's back to the dealer, on demand.



Compact, with huge bearings, the Audi parts on the PKT were designed to go 7x longer without a check-up - 105,000 miles.

The PKT extends or retracts in real time in reaction to actual belt length and dampens torque fluctuations.

You can now have a warning light with a PKT if you want.



Why are we still having this conversation?

PorKen

First time on the internet tubes?

Here's a hint - folks only usually talk about bad experiences.

PS: there's also these folks called 'trolls' who amplify these rare events to try to make themselves relevant.

GlenL

Because you say things like this:

What does that even mean?

"Real time" is a nice touch of jargon but every mechanical part on the engine is working in real time.

It doesn't react at all to "actual belt length." It reacts to the force applied to it.

"Dampens?" Really? I'm sure you mean "damps." Rain dampens things but a shock absorber (AKA a "damper") damps. That's a common mistake among the casual users.

I'm most interested in the "torque fluctuations." Torque where? And what fluctuations? I thought the harmonic balancer (AKA "damper") did that. Amazing!

So ya see, it's the word salads and broad claims that bother me.

Nice that you're offering a warning light version. We can look forward to that first post where a guy has his car flatbedded home because it came on when he gunned it.

JET951

GregBBRD is 100% correct in regards to the standard ( Factory ) 928 oil filled Bi metallic cam-belt tensioner . I have been working on Porsche road cars since 1977 ( 40 years ) and in all that time I have worked on all the road registered Porsche models/variants sold to the public here in Sydney Australia & the 928 ( all its variants ) & in regards to long lasting /robust components that give no issues at all , the stock standard cam-belt tensioner is a standout

So why anyone would discard it is complete madness , its one of just a few components that never ever need replacing if serviced correctly at cam -belt replacement interval & boy is it easy to look after , meaning keeping its internals clean & oiled , meaning replacing its flexible boot every cam belt replacement interval ( super simple & cheap ) & from 1983 , replacing the rear of tensioner gasket , again simple & cheap

And thinking about it , a few times we have replaced a cam-belt , rollers & water-pump on a 928S /S4 etc that we have never serviced or repaired before & the cam-belt tensioner had been ( in the past ) been completely neglected , so much so the the boot had gone hard years & years before & the boot had crackep open & the interior of the tensioner ( bi-metallic ) disc pack is seized up & full of dirt etc , but yet the cam belt had not caused any issues , we just remove the neglected tensioner , dismantle & wash out /clean & lubricate & reassemble with a new boot+ clamp & gasket , all simple & inexpensive

Now, sealed hydraulic cam-belt tensioner/s , like on the Porsche 968 etc , these have been quite reliable , but saying that they do not last forever & can & will fail & there is no ( to my knowledge ) set time or mileage as to when to replace them with a new one , we generally get a clue to the condition when we remove the said cam-belt tensioner from a 968 at it due cam belt replacement interval & on the slow compression of its piston ( to lock it in its compressed state with a pin ) so it can be removed to replace the cam belt etc , now at this point we have found the action of the hydraulic piston to be abnormal & this is the only warning one gets as to its internal condition & if ignored the tensioner will fail , sometimes they will not compress at all ( seized etc ) , so with these symptoms one can reasonably say , this hydraulic tensioner is kaput

Interestingly we have other mechanical repair workshops near our shop and at least two of these other workshops work on quite a few ( this century ) Audi's & its interesting to see when they do cam belts etc on these " this century" Audi's ( V6 mainly ) , they purchase what I would call Master cam belt/rollers Kits & interestingly these master kits come with a NEW Hydraulic ( sealed ) tensioner & when I enquired about this the shop owners simply mention that they would not dream of installing a cam belt & rollers on one of these V 6 Audis and reuse the old hydraulic tensioner , same goes with the water-pump , like on a 928 its gets replaced at the same time , but I get the impression , because the master kit ( comes with the hydraulic tensioner ) its not that expensive & they are not willing to take the risk of not replacing it

Regards
Bruce Buchanan
Buchanan Automotive 40+ years working on Porsche cars

PorKen

As opposed to the stock tensioner which just sits there as the belt rolls over it, the PKT extends to take up extra belt length created when the belt is stretched between the crank and cam/pump gears, instead of letting it stack up and flap (EG. when cold or at high rpm).

Tomato, solanum-lycopersicum.

Admittedly, that is bad englishing. Uneven torque pulses make more or less free belt between the crank and 1-4 gear which the PKT reacts to, in 'real time'. You'll see this mostly when cold where the tensioner/damper piston will extend and retract rapidly at idle. (Markedly so, during the 3-minute warning light embargo.)


Because the stock tensioner doesn't do much of anything except stretch the belt? It is, for-all-intents-and-purposes, a fixed tensioner. Not much to go wrong there.


If anyone is going to drone on about the bi-metal Belleville washers actually doing something, please step up and for once prove it, with measurements of its extension capabilities, hot, cold, under tension.


Better yet, and easier still, run the engine with the center cover removed. Seeing the belt flap, uncontrolled, when cold and at high rpm should be eye-opening, enough.

JET951

Hi Ken , its funny you should mention "Stretch the Belt " , because I /we have one particular 928S4 customer that before we knew the said 928S4 the PO had installed a Porken Tensioner and the one thing I / We have noticed is when the engine is cold & in the warm up mode the Cam Belt tension is way too high because this engine / timing case emits a cam belt Over Tension noise , yes you know the noise , its the noise you get when a cam belt ( on any car engine ) is too tight or out another way the tension is too great , but as the engine warms up the belt tension decreases and the "Cam Belt Over Tension noise is less .

So my question to you= is that normal for the Porken Tensioner system ? , meaning the way too tight noise the cam belt exhibits in the cold to warm up mode but not as noisy when the engine is hot and expanded ( where the noise should be worse ) , its a reverse situation

And no, the standard Porsche 928 Cam belt tensioner does not stretch the cam belt , because we only ever adjust the cam belt once after about 10,000 Kms ( free of charge ) and takes us 15 minutes to do and thats it until the next cam belt replacement interval years later

Remember if its going to Stretch the belt , the cam belt would have to exhibit a over tight noise that all cam belts make when too tight & the stock tensioner if adjusted correctly simply causes NO noises at all

So this means the one we have ( Porken Tensioner) is over tensioning the cam belt ( which has to stretch it ) in the warm up mode , I would like too know why

Please do not get me wrong , I admire you ingenuity in the "Porken Tensioner" , I am just puzzled because you have answered a question I have never found any one ask , like "We Need A Better Tensioner For The 928 " , but I can not fault the original at all , not even a tiny bit , its damn hear perfect

However if you had come up with a clever invention to help fix the BIGGEST stuff up on a 928 ( design Stuff UP ) be it ALL the manual trans versions or the 928S/S4/GTS Auto Trans 4 speed auto's & that the Rear of the Torque Tube weak rear coupling with its way way way under engineered SINGLE index bolt set up & the stupid input shaft CUT in 3 places , now theres a Joke of a design that needs reinventing , but its a very difficult one to fix & I can understand why every one has just given up

Interestingly the 3 speed Auto Trans had two solid shafts meeting end to end with the 944 sliding sleeve over the top with two index bolts ( no problems at all )

Regards
Bruce Buchanan 40 + years working on Porsche cars

PorKen

I have heard that noise with some new installations, when cold, especially with Continental belts, but it goes away after the belt settles in. (The sound of the belt meshing with the gears?) When the Audi tensioner/damper is cold it takes longer for it to retract.

It is not a noise that you would hear with the standard tensioner because the belt is looser when cold than hot. Recall that this is the worse time for reduced tension as the engine is not firing evenly.

What belt is that S4 running? How worn are the gears? Is the Audi lever and pulley moving freely? I have heard of a couple of cases where people have not installed the rear washer on the pulley and it did not move at all!


All belts stretch. Over time the belt gets longer, but it will still have some stretch = tension. The standard tensioner is stretching the belt just a bit more than is necessary to keep the belt engaged. For the 32V engines, the tension was increased to compensate for the additional load of two more cams (+ 16 followers, 32 springs, 2 timing chains). Higher load means more belt stretch when running, which creates more belt length on the tensioner side (more during acceleration and at high rpm). The standard tensioner cannot absorb this extension so the belt has to be pre-stretched to reduce this effect. Only a proper hydraulic tensioner/damper can actively manage this extra belt (at a lower running tension).


Thank you. I differ and find fault in the stock tensioner.

Properly maintained, the stock tensioner will keep the belt on the gears, but it is only barely up to the task compared to a modern system. The standard tensioner system is substandard when the engine is cold and does nothing to stop the belt from flapping at high rpm, hot or cold. (Porsche acknowledges the stock tensioner's shortcomings with a 3-minute delay in showing tension warnings after startup.)

The stock tensioner requires comparatively low mileage service intervals which new owners are not accustomed to - hence the reason PKTs are being installed more and more often as 928s change hands.

You mentioned Audi engines in regards to changing the tensioner/damper at belt change. What is the service interval for 928 tensioners? The Belleville washers must have a service life, correct? (I found very little movement with 120K mile units.)

Speaking of Audi engines, there isn't much talk on the 2.8/30V forums of "let's replace the automatic tensioner with a manual one, bro", "we'll have to check and adjust the tension ourselves, and it won't control the belt as well, but it will be sick, yo".


I recall some conversations here about it (Stan), but I don't recall as many complaints about the rear coupler as much as the front. Perhaps it has been neglected because it is difficult to access.

I was the first to sell a clamp for the front coupler which helped reduce shaft creep (PKlamp). I used to sell clamps to reduce the front coupler noise on manuals (PKalm). I make a tool to easily adjust valve timing (PK32V'r), etc. etc. - http://liftbars.com

docmirror

I grabbed up my engineers handbook of spring rates, and coef and was going to go on a long, involved drone regarding Bellville washers. And then, I figured 'hey - someone with way too much free time prolly has the online version'.

yup. https://en.wikipedia.org/wiki/Belleville_washer

the equations for the spring rates is in there, go ahead and do the math if you so choose. Since we are using a stack(4 stacks, in opposition as I recall?), don't forget to subtract for the friction coef as well.

The stock tensioner does adjust for engine growth. It was the 70s answer to slack-belt path in a large thermal conductor and as has been said ad infinitum, if it is kept in good health, will provide good service for 40k miles.

Yes, the piston tensioner is better, yes, the piston tension, and modern thick belts are designed for 105k miles. Who knows why that is?

Answer; The state of CA determined back in 1983 that the timing belt was part of an 'emission device', and as such had to be built to last for 10 years, or 100k miles. Just like the cat, just like the air pump, just like the PVC valve. Which gave us very robust and duty hardened belts and tensioners.

BTW, Belleville stack washers in hyd fluid are used on a number of medium and small aircraft shimmy-dampers for nose gear wheels.

Imo000

It doesn't matter what the belt does on the 928 when cold or hot, the factory tensioner is designed to work withing those parameters. Porken, just because you think there is a problem it doesn't mean there is one. The factory warning system in a life saver. Said it many times that it saved my bacon and for that feature alone, I'm never changing to the Audi tensioner. The warning light that was shoehorned to your system is not even proven to do much more than to throw the light when the belt breaks or is so loose that that it is in the process of jumping.

PorKen

Bold statement. Prove it!


Folks have said this since forever, but I've never seen proof. "But, Porsche said it does" means nothing. They have routinely been wrong. EG. removing the circlip on the torque tube shaft because it's "not needed". Great idea.


Perhaps like this? Take a beam torque wrench and measure the torque on the bolt to reach 32V tension at 20C (shop temp) . Fab a rig to hold the stack assembly so that a bolt can press the washers to that bolt torque. Measure the stack height at 0C, 20C, and 90C. Do this with new, 50K, 100K mile stacks. Report back.

Until then please, people, at least say "may adjust for engine growth".



FWIW, I measured and got roughly 2mm with a 120K mile stack from free length to being squashed in a vise. Way out of installed norms, so actual maximum would be less. Temperature wise, un-tensioned I saw 0.5mm difference between 32C to 0C. Working with the PKT, I see a difference of at least 2mm pulley movement from cold to hot is required.