grepin

So I just installed my first Porken tensioner with a Gates Race belt. It seems a little tight as referenced by the Kempf tool. I have not driven it yet so things will loosen up. I have about 3mm gap on the tensioner.

Thanks and Merry Xmas.

FredR

To measure the correct tension with the Kempf tool and the stock tensioner you have to take the measurement with No1 cylinder at TDC on the firing stroke. The reason for this is that the static belt tension changes as the cam resistance changes. How that translates when applied with the PKT installed I have no idea but my logical way of thinking tells me you cannot use the Kempf tool with any meaning of significance.

I have never seen this matter discussed on the list as the entire point of the PKT is "fit and forget". It will be interesting to see what the general consensus is.

grepin

Yeah I bought a Kempf before I intended to go the Porken route. Out of interest I thought I would try it. Now you mention it I am not one hundred percent sure It was at TDC. Easy to still try. It would be interesting to see over many thousand of km/miles how much it changes.

FredR

Greg,

The PKT by design keeps a constant tension on the belt. The stock tensioner varies with position and to some extent temperature. The Belleville washer pack tries to compensate for this but I suspect it only does this to some extent thus why the belt tension alarm system does not cut in until the motor has been running for 3 minutes - the logical time it takes to warm the motor up.

On the other hand if the actual tension falls within the movement range of the gauge it should demonstrate the same value irrespective of crank position.

grepin

Thanks Fred,

I guess my only concern was if the PKT is generally tighter than a correctly set up standard tensioner would that cause excessive gear wear. Something I just replaced all of as my originals were excessively worn. However the PKT is well tested now so I probably don't understand the physics of it. Anyway for a first time TB job it was a way easier idea than servicing the original.

FredR

Greg,

Getting the correct belt tension with the stock tensioner is critically dependent on the position of the crank it is calibrated for. Common sense tells me that as all cylinders fire at 90 crank degree intervals it should not matter whether the engine is on No1 TDC or its alter ego 360 degrees later however I religiously stick with No1 on TDC firing stroke and leave it at that.

With the PKT you mount it, pull the pin and that is the end of it. Given the tension variations are taken out it stands to reason that the PKT produces a higher tension than the stock item at the specified measurement position. Thus the stock tensioner method is inferential in that if the stock procedure is followed one will end up with the correct tension when the motor is fully warmed up.

Mrmerlin

I would suggest to put on a stock belt unless you have stronger valve springs.

NOTE the Porkensioner was made to work with a stock belt and it runs at a lower belt tension
That Racing belt is stiffer thus it will be less compliant with the belt run compared to a stock belt

dr bob

Measuring belt tension with a Kempf tool and PorKensioner is a bit of a conundrum. The tool works by twisting the belt, essentially stretching it at a specific spot. Great with the stock tensioner, as the spring washers in the stock tensioner have a very steep pressure slope. The PorKensioner has a not steep slope, intended to maintain a very constant tension over a larger range of travel. Twisting the belt with the Kempf tool typically gives you a higher initial reading that quickly fades lower as the Porkensioner adjusts. You can easily verify that by holding the Kempf tool at full twist, and watch the reading fall slowly to settle a bit below the normal tension window.

Bottom line is that, while an interesting exercise to verify that the tensioner pin is pulled, getting a reliable and repeatable tension reading is all but impossible if the PorKensioner is working properly. The actual tensioner piece is something that should probably be replaced periodically per Audi's recommended life predictions, but is otherwise a plug-and-play solution in Ken's bracket.

** I have installed a few of these on clinic cars over the years and love them for their simple elegance. Meanwhile, I still have the original tensioner installed in my own car, with working warning light and all. I may change someday, or may just keep putting new rubber bits in what I have every seven years or so.

PorKen

Piston extension will probably increase when the engine is turned over with the starter and the belt settles into the gear teeth.

The Kempf tool may show high or low with a PKT and the measurement may change as the T/D reacts to the belt twist. When the T/D is cold it will take longer to retract.

A used regular belt will usually show an additional 2 mm extension when the belt has over 1K miles. Racing belts take a long time to show any stretch at all. When the engine is hot the extension shrinks about 2 mm.

PorKen

Meh.

The Audi parts were designed for a essentially a wider Racing belt with a 105K mile belt change interval but happen to work well with thinner floppier belts, too.

Less compliance requires the tensioner to absorb fluctuations. Once hot, the stock tensioner has no spring or damping capability (Bellevilles are flat).

FredR

Ken,

Some interesting input there. The stiffer belt indeed should require less damping. Your perception of the Belleville washers being flattened puzzles me some. The research I did some time ago suggested they are not maxxed out until some 180C. As installed in the engine bay I reckon the damper is going to be operating at or around 80C so plenty of "range" left in them. I measured the contraction between zero C and 100C - I forget the actual contraction I measured but figured it was consistent with the engine growth I calculated and the washers looked anything but flat for whatever that may be worth. Having studied the design of the stock tensioner I figured that it would indeed absorb pulsations and that the oil in the body plays a role in damping that process. The first incarnation of the stock tensioner was simpler from that deployed from around 83 onwards that has an outer annulus and a check valve in the body. I figured that the oil absorbs some energy, heats a little and circulates around the body to cool it appropriately the chatter of the washer pack acting like a pump as it were. Porsche took patents out on both iterations and I suspect there was a good reason why they did such. The Belleville pack itself has a spring rate equivalent to 0.6 compared a single washer- I could actually compress the pack slightly with my fingers and the total number of washers determines the actual travel range- it really is quite a clever piece of kit in its own right- I doubt there are many folks around who really understand how it works.

As to how well the stock tensioner acts as a damper I cannot really comment. There is something that concerns me and that is why the cam sprockets show wear predominantly on the flats whereas I expected to see such on the leading edge valleys of the sprocket teeth. Given the flats seemingly wear the coating, this tells me the teeth are not fully seating in the valleys correctly. This made me wonder if when designing the belt, Gates were given the sprocket dimension before the coating was applied. For years we would read about how wear of the coating would cause the timing belt to shear on the sharp edges but I often wonder if anyone has ever seen evidence of such?

Similarly, the timing belt alarm appears to have created some false perceptions. As to why Porsche designed such into the system remains to be seen but I figured they put it there as a form of insurance just in case the tensioning bolt backed off due to vibrations. The belt surely does slacken off a tad after the initial bed in period but not enough to jump a tooth- after that I have never noticed anything. The belt tension alarm itself says something like "Timing belt service"- it does not say "Tough luck pal you have bent 32 valves" With the PKT that bolt is eliminated so arguably no need for an alarm but it did not stop others chiming in about "how it was needed" on the PKT.

At the end of the day it is not the tensioner that demands how tight it should make the belt, it is the system it is tensioning and that is likely decided by the belt manufacturer unless Porsche provide design criteria for the belt. As I could fathom out it was Gates who advise the engine designers about such- it is part of their skill set/service. Thus I figured that whether one uses the stock item or your PKT the residual tension should be the same in round terms. Whether that is the case or not I have no idea. That you managed to package the PKT into the space available was quite brilliant as I am concerned. My perception is that the spring inside the Audi item operates over a narrow range thus its tension is more or less constant but of course that limits the range of extension- generally not a problem but as you came to understand with experience, not all examples have the same requirements thus how your design evolved.

Mrmerlin

The point I was trying to make was that the racing belt is not a necessary part on a belt run with stock parts with the exception of the PKT being used.
and since the PKT applies less belt belt tension compared to a stock tensioner,
adding a stiffer belt might not be the best thing for the belt run