GregBBRD

If you've followed this exchange (and prior ones) of ideas about belt tensioning, obviously, Porken and I disagree on the value of his tensioner system. That's cool...it is a free world. I know that there a lot of happy people out there with his system and I respect that. It simply doesn't do what I need to have happen on a 928 engine. I need constant pressure that doesn't allow the cam timing to change.

That being said, I own the factory tool to set belt tension and use it on every belt. I have never had any problems with a factory belt...I have had some issues with aftermarket belts. If I didn't have the factory tool and I was a "do-it-yourself" home repair person, I might have different ideas about Ken's system. Although it never gets the belt close to the factory suggested tension, it at least has the ability to keep the belt at a constant, lower tension.

Keep in mind that there are literally millions and millions of miles on the factory system and the newest one on a vehicle is over 25 years old. Are the pieces/bushings worn out and will there be parts needed? No doubt. Can I still get the pieces????Absolutely.

Is Ken's system really simplier? Not really. there are actually more bushings, bearings, and hardware in his system that on the stock one. Granted, all the bushings are provided already pressed in, but they are still there. Are they going to wear over a 25 year period? You bet. Are you going to be able to get pieces for them???? Well, don't throw that stock stuff away.

I've asked Ken many questions about his system, over the years, and the "hard" measurement data is non existant. That makes it tough for a pure mechanical guy like me to us his stuff. That should be cool. However, Ken prefers to personally attack my credibility to distract from his complete lack of emperical engineering...just read through a few of his posts, right here.

Heh, I've no axe to grind here. I don't make money when people buy the stock stuff...or Ken's stuff. And Ken......well, if Roger has made "a lot of money" selling Ken's stuff...imagine what Ken has made. He does have an interest....and don't ever expect him to conceed any point about his system. He will instead say things like "3.7 was the tightest was the tightest you measured by turning the engine by hand. At no point did you turn the engine with the starter or run the engine."

Ahhh. the magical "Porken" force...changing the universe and all previous physical knowledge. Read the following carefully and slowly: The tensioner will only push that idler to tension the belt to 3.7 belt units...anything more than that and it retracts...belt sitting still, belt spinning, belt turning with starter, engine running. It simply doesn't matter...physics is physics...and this is elementry physics. It can't push and harder than the force of the spring within the tensioner...no matter what. And that is 3.7 belt units.

PorKen

Cam timing doesn't change with a PKsn'r, anymore than it does with the stock system. This is just a anothing thing GB has made up in his mind, but hasn't tested properly. Many, many people have successfully used a 32V'r and PKsn'r without issue.

The Audi T/D is hydraulically stopped. It's not just a spring which holds the belt in constant tension.

High tension is for old non-self adjusting sytems (like GB ). 'Belt management' is more important than some number.

Hundreds of PKsn'rs have been running just fine in all conditions since 2006. (And thousands and thousands of Audis have been running since '98.)

blown 87

Let me get this straight, you are saying that cam timing does not change with belt tension right?

PorKen

In that quote, I'm saying the the 32V'r gives consistent results when used according to the directions. What is unclear?

blown 87

Your answer to my question is unclear to me Ken.

I am asking if you are saying that cam timing does not change with different belt tension.

PorKen

I'm not saying that. Would you like me to read it aloud for you?

76FJ55

Does anyone know how much torque it takes to drive the cams when the engine is running? Also what is the modulus of elasticity of the belt (Does Roger have this from the new Racing Belt project with Gates)? Without this information I do not believe that it can be determined if the PKns'r of the OE tensioner actually applies more tensioning force when the engine is running. Since the PKns'r is a dynamic spring loaded system it in theory will hold the tension constant whether the engine is running or static, however the OE system is only pretensioned and then essentially held in static position (for a given engine temp, so disregarding the bimetallic washers).
To know which one has the greatest tension during operation you would need to determine the amount of elongation in the pulling run of the belt from the crank over the oil pump gear, 5-8 cam, WP and to the 1-4 cam and then add this amount to the length of the slack run from the 1-4 cam over the tensioner and to the crank. You would then need the stiffness coefficient for the belt. You could then take the initial tension in conjunction with the measured length of the tensioner run of the belt and the additional length needing to be tensioned due to cam drive loading to calculate the new tensile load applied by the OE tensioner. You could then compare the resultant tension from the OE system to that of Ken’s and see which has the highest tension during operation.

Louie928

Cam timing should be done with a used belt bedded in with the sprockets in use. Then put on the new belt. If you don't want to do that, then get timing close with the new belt, but don't spend a lot of time trying for exact timing. Drive the car for a couple thousand miles and then refine the timing.

blown 87

So I can deduct from "I'm not saying that" that you agree that cam timing does change at different degrees of belt tension.

I am not trying to be combative here at all, just trying to get it through my thick skull exactly what is going on, not just "This is the way it works".

How are you measuring the belt tension at static and with the engine running?
And how do these figures compare with the readings from a 9201?

And how did you determine what figure was correct for a 928 with its seven foot long belt?

jpitman2

Surely the spring in the Audi tensioner (and any device with a spring in it) is at its highest load when its shortest? If the Porkensr roller moves in and out with rotation while being hand cranked, does it do the same while running at steady rpm, and if so why? I understand (I think) that at some points the cam will want to advance due to valve spring forces applied to the lobes faster than the belt is moving when being hand cranked, but I would have thought that even at idle this effect would be negligible. Such tendency to advance would be the origin of the slack side of the belt being pulled, and compressing the tensioner, wouldnt it?
jp 83 EuroS AT 52k

Ed Scherer

How revealing would it be to mark the cam gears every 90° (starting with a carefully calibrated mark at #1 TDC and then trying as best as possible to make marks at the other three points based on relative distance from the teeth) and then inspect with a timing light synced to the appropriate cylinder?

And does anyone have any idea at all what the forces on the belt are between each vertex in both static and various (RPM) dynamic conditions?

It gets even more complicated when you consider the inertia of each component. Wouldn't a constant RPM (other than 0, but at least idle) likely yield a steady state that's almost certainly acceptable, but rapid revving possibly lead to significant advance/retard? I suppose what I'm considering is that differences between tensioning (belt management, whatever) alternatives might manifest themselves much more in the static configuration and during revving much more than during constant (but engine running, i.e., non-zero) RPM.

Pretty damn interesting modeling problem, complicated by the lack of information. With enough measurements, though... there might be hopes of developing a pretty comprehensive model.

(I'm an EE/CS guy, not an ME, so these are just uninformed musings. I didn't even stay at Holiday Inn last night.)


Bottom line, though, IMHO, is that it becomes somewhat academic once enough real-world results come in. Seems like the PKsn'r has racked up a good reliability record (which was my main motivation for installing it, along with ease of maintenance), but I have to admit that the possible effects on timing do have me interested enough to continue following this debate. Hope it stays reasonably civil.

BTW, after I installed the PKsn'r with a Gates (non racing) belt, the Kempf tension tool read out a little under halfway in the window. I'll obviously be taking another look after I clock some miles and go back to check the belt tension, adjust timing, etc.

You guys know way more about this stuff than I do: it's my first TB/WP job, so I greatly appreciate the discussion and opinions, varied as they may be.

GregBBRD

Found hanging in Ken's garage? "Blow enough smoke and hope no one asks anything technical. When they do, claim they are uninformed."

If you re-read your post #36, you have never checked the cam timing while the engine is running! You invented/make the fricking thing.....and you've got the ***** to say "he hasn't tested properly"?

Seriously?

Lizard928

With all respect, have you tested the belt tension while running with the stock setup?

The cam timing will change more with the stock system compaired to the new system.
Because of this the factory ran with a higher belt tension.

I say this as the cam loves are being pushed by the valve springs it changes the belt slightly (load vs unload)
Gb should know this better than anyone, you must check the tension at #1 TDC as per the manual. If this was not the case why would they say this.

I am also curious if anyone has checked belt tension with the stock system at full race operating temp as the motors expansion is great.

Tampa 928s

Not to change the subject, but is it possible that his dampener is moving? I found two loose ones on an 86.5 and a 85, the timing kept changing on the cams. The dampener was shot and TDC was not TDC back to the regular scheduled programing.

GregBBRD

If this is a question for me?

No, I have no way to check the belt tension on a running engine.

How can this be? The stock tensioner has no give, when you try to compress it....only Porken's system allows the tensioner to compress. Tht's why the piston moves in and out when the engine is running, with his system....watch it, at work. Never greater than 3.7....but much less when the cams push backwards with spring pressure.