123

Since there's always mention of the tensioner being used on the 968, how long is the 968 belt compared to the 928 one?

Porsche built the 968 from '92 to '95, the same as the GTS. If they went to the trouble to implement that tensioner on the 968 for only the short time it was made, would it really have been that much trouble to implement it on the GTS too then? There were a lot of changes made to the GTS from the S4/GT that were a lot more trouble and expense then adapting that tensioner to the GTS engine would have been, so why didn't they? They went to the trouble and expense to put it on their entry model car, but not on their top of the line model car, even though they were both made at and for the same length of time?

I'm not knocking Porken's tensioner, but it just seems like it wouldn't have been a big deal for Porsche to have adpted it to the 928 engines if they would have thought it was a significant improvement.

PorKen

The 928 detensioner has no spring. (The Belleville washers inside will flatten somewhat as they get warmer, but they do not have a large range.) It cannot increase tension over what was adjusted at the last service, and cannot compensate significantly for an engine temperature colder than at that service time.

The 968 has a self contained tensioner/damper like the PKsn'r.


The only length that matters to the tensioner is the distance from the last pulley/gear to the crank gear on the slack side.

dr bob

The stacked Belleville washers in the 928 tensioner are the spring. The amount of effort required for compression of the washer stack is not very linear, somehat similar to a coil spring that operating in the 'coil bind' range. So long as the belt stretch and wear components are minimal, the stock tensioner is more than adequate design. (dr bob emphasis added). Note that this very non-linear operation is what allows the factory warning system, with it's coil-spring 'reference', to function at all.

The amount of shape change in the washers with temperature change is negligible. The theory that the plated Belleville washers somehow adjust to engine expansion is borderline hogwash. It's straight differential expansion in the domed shape that does the work, such as it is.

Using a different spring with a longer travel and linear characteristics makes a whole lot of sense as far as managing belt tension during engien thermal expansion. This is how Ken's product works, along with the oEM pieces used on almost all cars manufactured today. There's just no good way to warn the driver when wear on or damage to components has become excessive. With the linear spring, the only warning availabe is from excessive extension of the spring/piston as parts stretch or wear. Common limit switches are not that precise.


I'm not saying that it's less than a great product. For many owners it's a great option. Without the wear warning, it's just not the right one for me. Personal opinion and preference. I am watching the discussion with grea interest though, and remain open-minded.

ROG100

I would not expect Greg or Blown 87 to use the PKensioner unless they were specifically asked to do so by their customers - one day when the system is soooo well established they may venture down that path. I fully respect that point of view.

Judging by the numbers I sell v the original tensioner their is no contest. I would add that I am the only seller as far as I am aware, so that scews the numbers a little.
The PKensioner is in use in Australia, Europe and Canada as well as in many cars in the USA.

I agree about the early cars (78 to 84) because replacement of the original system can be cheaper.

The original system was designed back in the late 60's/70's and technology does move forward.

The PKensioner is maintainace free and keeps the belt tensioned correctly at all times.
The system is used on most modern cars in one shape or another and is well proven.

If PorKen was English he would be up for a knighthood in my book.

A large number of cars in the DFW area are fitted with the PKensioner and even the great "Sterling Gee" has one fitted to his monster - car that is 8>)

The Porsche and Gates belts are made on the same drum and the only difference is the printing and the price. I only sell Gates belts and perhaps one Porsche to every 100 Gates belts.
Recent OEM belt suppliers have been Continental and Flennor (a Gates company).

jcorenman

Err, uhmmm ... the washers are described in the tech literature as "bimetal discs". I've always assumed they where there for temperature compensation? Otherwise they are so stiff-- as you noted-- that there would be no reason for them at all. There either needs to be a spring with real damping-- to avoid the problem Greg Brown mentioned-- or a rigid device which somehow compensates for changing temperature.

This is from the '78 service info bulletin:
The other thing that is key is the hydraulic dampening. The Audi tensioner (and I assume others) have valving which allows them to take up any loose tension quickly, but they give it back only slowly. You can readily see this with Ken's tensioner-- pull the pin and it takes the slack right out, but in order to get it back you've got to lean on the wrench for a while to compress the rod again. Pretty slick, and exactly what is needed.

We certainly agree on the need to periodically check things, no matter what tensioning system is used. It's not hard to do in either case, but the PKensioner is particularly easy to check-- just a flashlight and a mirror.

But why not also add a switch contact that would warn of the tensioner rod getting near its limit? I am guessing that could happen with those trashed sprockets of Dwayne's

Cheers, Jim

jcorenman

You think???

the flyin' scotsman

While we agree that it'd be nice to have a warning on Kens tensioner I'd question the amount of warning has with the OEM tensioner thats getting beyond half its maintenance life cycle.

OEM is what it is from the time it was designed in the mid '70s which is now going on 35 years; it leaks oil, its bearings fail, the pivot arm twists, requires maintenance and worst of all is known to have failures that cause the timing belt to fail and destroy the engine.

Kens tensioner works, keeps constant belt tension, doesn't leak oil, is robust in design and manufacture and saves many engines/cars from being scrapped.

I fitted one of the early Pkensioners when Ken sold them direct and have had zero issues including the new belt fitted (Conti) at the same time and no issues with any gears............30k kms

I was so confident in Kens product that after the first year I sold all of the OEM tensioner and never looked back.

Stromius

I'm with the PNW/Canada sentiment too - I've had my 'ah ha!' moment and thing this advances our cars and shows innovation with folks like Ken (tusen tack!).

I am a noobie to these cars 3 years in - still. The TB job is THE urban myth that none '28ers warned me about when I was shopping. It's 20ft long, complex, has its own gravity field and made of platinum etc . Well my TB replacement and Pkensioner job was a treat and really got me comfortable with the engineering and helped demystify my S4.

I was explaining this thread to my wife she said.."kinda like parenting - 'when you know better, do better' ". Much like parenting indeed, TB lore and tensioners is an individual thing. Like others, I too respect the OEM leaning crowd. Mine stock tensioner even still held oil when I took it out! Still I can't help to marvel at the simplicity of Ken's innovations including the Pkensioner, timing tool and all those S2/3 items.

I'll be happy to add a warning system if it comes along too but for now, it seems to work just fine.

A parting question....what are the Panameras and Cayennes using? Just curious what Porsche decided with V-8's?

GregBBRD

Yes, indeed this will happen....but only if you are stupid enough to use a crappy belt.

You'll find that this only happens with an "aftermarket belt", which I've called "giant rubber bands", more than once. This will never happen with a high quality/Factory belt, even if the belt tension drops below 3.0.

GregBBRD

Brilliant, you are.

GregBBRD

Actually, I did have an "ah ha" moment. This came after carefully studing the design of Porken's tensioner and then calling him and asking him what kept his tensioner from collapsing when there was a "backforce" applied to the tensioner that was larger than the spring pressure that kept the belt tight.

You guys need to be really careful when you are comparing belt tensioning designs from one vehicle to another. "The 968 essentially does the same thing as Porken's tensioner" is an especially bad example.

Note that the 928 design has the tensioning "wheel" located very close to the crankshaft. This means that any "backforce" has a great deal of leverage on that roller. The 968 engine has the tensioner "wheel" moved much farther from the crankshaft.

Note that the 928 design has a "smooth" wheel that tensions the belt and that the 968 design has a wheel with "teeth". This makes tooth 'slippage" much harder on the 968 design, since the belt needs to actually "jump a tooth" at the tensioner to "jump a tooth at the crankshaft". Not so, with the 928 design.

Note that the 928 belt design pushes the belt towards the center of the engine. This "direction change" makes any backwards leverage on that pulley very extreme. Note that the 968 design pushes the belt from the center of the engine towards the outside of the engine, reducing the effect of any backforce.

Porsche knew that the location of the tensioner and the leverage of the belt made the odds of the belt slipping a tooth when the belt was loose much higher than normal. Thus the warning to "never turn the engine in the counterclockwise direction".

Heh, I've got no axe to grind, here. Everyone is welcome to make their own choice and do whatever they want. I choose to use the factory belt and factory tensioner for my own reasons, which I've tried to detail.

Here's what I do know:

You can buy a factory belt and but the pieces to rebuild the factory tensioner cheaper that you can buy any "aftermarket belt" and a Porken tensioner.

"You pays your money and takes your choice."

Jerry Feather

Don't be surprised to find that your water pump is failed and making the noise that is getting your attention. Good Luck.

Jerry Feather, FBA Certified
S4's (6)
KGJT

davek9

OK my 928 cents

I have installed Ken’s tensioner system and like it, simple and quick less moving parts.
Less moving parts is always less prone to failure simply because there is less to fail.

I can see how it works and it should/does work better at maintaining a consistent pressure (tension) on the belt throughout the entire temp range.

The stock system is really a "de-tensioner", it’s there to set the static belt tension and to compensate for block/head expansion.
I am on the side that does not believe it can offer very much in the way of dampening.

With all that said, I continue to run the stock unit, having rebuilt it and replaced ALL the gears and pulleys. However I routinely check and maintain the stock system checking oil and belt tension every spring.

I am considering changing over to Ken’s system only because it is designed to maintain a consistent belt tension no matter what the “start-up” temp and should save the gears/WP from unnecessary wear.
I think it does need to incorporate the factory warning light (maybe w/o a delay?). The light does give an indication of ANY problems w/the belt system in general, and without the light… well I guess you will know but won’t have a warning that could limit damage.

This is not a deal breaker for me as I like the design, less and more durable moving parts and I will most likely install Ken’s system at the next opportunity. But l still will continue to follow my yearly spring routine.



DaveK9

Tails

It is just a matter of choice, so be happy with what you have got and respect that others have a right to have a different opinion. Opinions can change if a product gets a bad reputation for failing.
Tails 1990 929S4 Auto

GregBBRD

Here's my tensioner story....which has nothing to do with 928s....but might give you insight of why I study things very carefully and ask a whole bunch of questions, before I just assume that a "new design" is better than the factory stuff.

You guys have got to realize I've been working on only Porsches for over 40 years....and that is all I do....day in and day out....year in and year out.

This is a 911 story. 911s had terrible tensioner problems, until Porsche came up with the "Carrera" tensioner in 1985 model year. There were about 6 versions of "Porsche" factory tensioners before they came up with this design.

Not sure exactly when, but I'm going to guess that "a company" made a "bullet proof" tensioner design back in the late '70s. This looked like a great idea. No oil, no hydraulics. Just a spring on a shaft and then a "ring" of very small ball bearings on the shaft that allowed the shaft to only be pushed away from the body of the tensioner. The spring pressure would push out the shaft and the "ring" of ball bearing would prevent the shaft from collapsing. Pushed on the idler arm and kept the chain tight. Simple! Brilliant!

Worked great. Installed dozens of them...almost all independant shops used them...they sold hundreds and hundreds of pairs. Became the "go to" tensioner whenever the factory tensioners failed (which was often).

After a couple of years, we started to see tensioner failures with this design and the resulting "valves hitting the pistons" that happens with 911 engines. Well. it turned out that the designer had not anticipated the up and down force on the shaft. The ***** would get a little flat spot in them and allow the shaft to collapse....which instantly turned the engine into trash. Of course, the company had no product liability and instantly disappeared.

Guess who got to call all those customers that had these tensioners installed and pay to change them?

I never bothered to ask:

Does Roger or Porken have product liabiltiy insurance on the Porken tensioner to protect all of us?