j.kenzie@sbcglobal.net

With the rollers correctly installed but the PKT not correctly installed, maybe only one cam would jump 8 teeth. If the belt was loose enough to jump off the crank gear, but was constrained there it probably would have jumped somewhere else. The rollers are not there to constrain a consistently loose belt, but to restrict oscillations in a properly tensioned belt with the conventional tension system.
JMHO
Sorry,
Dave

ROG100

I agree in the standalone case of the crank gear, however if there is wear on the cam gears, oil pump gear and some slight wear in the water pump bearing - the compound effect is significant - read perfect storm.

Hai gebissen

Except the cam gears, oil pump gear, and water pump were all new at the time of Racing belt and Porkensioner installation.

j.kenzie@sbcglobal.net

Once again, it would be nice to know what one millimeter of tensioner extension gives in terms of belt length. If the belt is loose at 9.5 mm extension, how much tighter would it be at 5 mm? The way I understand it, the tension will be very constant within the specified range, then drop off very quickly.
Dave

Imo000

Maybe but shouldn't this system be designed to operate under less than perfect conditions. There should be some room for slightly worn components. I think it does have some room but I'm not sure how much.
Ken should be answering these and other questions raised as this is his product. If he doesn't have the answer then he should just say that.
I just realized today that the car I'm working on has a problem too with the tensioner system he made. This "radio silence" is frustrating.

GregBBRD

No. No.

GregBBRD

Sounds like you are saying everyone should install a brand new set of gears, for the Portensioner to be in the correct "range".

So much for the economical solution....

GregBBRD

I'm still waiting for someone to answer the belt stretch issue....I was hoping Ken would have done the reasearch and known this.....he's the "inventor", after all.

If installed at 7.0mm of extention, how long until a new stock belt (which does stretch) reaches the deadly 9.0 measurement that killed the OP's engine with a belt that doesn't stretch?

Sounds like a pretty short fuse, to me.


I can't imagine how fast 7.0mm gets to 9.0mm with an aftermarket "stretchy" belt.

j.kenzie@sbcglobal.net

OK the can't jump off the crank gear (with teeth intact) but if the belt becomes loose because its tension was wrong at the start or became loose upon stretching, the damage is about the same when the belt jumps cam teeth. Ken's system specifies a range of extension for the tensioner upon install with both new and used belts. It sounds like this was outside the range, and only got worse when the belt stretched from new to old size. A warning system would have helped, but knowing that there is no warning system, only makes it more important to stay within spec on the install. I actually don't think that Ken knew how critical that was, and has said as much. Here's what I would suggest for his design:
1. Figure out a loose belt warning system, maybe using the tensioner extension itself
2. Since most installs would allow tensioner within proper range, have a small supply of modified brackets that would be exchanged with the stock bracket, to move the tensioner into proper range at time of install.
These ideas have been mentioned before, nothing original. Just saying.
Dave

jcorenman

Tighter, and no. The Audi/NTN tensioner is a spring and a one-way damper, and like any spring the force goes up with more compression. It is not hard to test, you just need a fixture that can compress the tensioner a specific amount (e.g. any sort of shop press) and something to measure force (e.g. a scale). The tensioner extends quickly (to take up slack) but compresses very slowly, so testing-- when compressing-- must be done even more slowly-- or after a resting period-- to get accurate results.

I did all that a couple of years ago and haven't posted the results because I am really tired of being pissed all over by Ken. But the answer to your question is tat there is about about 50# of linear force at the Audi/NTN tensioner with 1 mm extension, and 27# at 10 mm extension. Roughly 2:1 over the operating range, and linear within those limits-- and same force whether compressing or extending. That's only a sample of one with around 75K miles on the tensioner, I am sure Ken has many more.

That's at the tensioner itself. There is a lever and a sliding contact point between lever and roller with uncertain lubrication, which introduce friction. At 4mm of extension, the resting force after compressing was 170#, and after extending was 46#. At 10mm extension the same figures were 90# and 18#. Again, a sample of one, 25K miles on the idler and lever, greased when installed and tested as they came off the car.

Statistically speaking, samples of one mean nothing and proper testing is done with many samples over a range of conditions (e.g. dry, oiled, greased, hot, cold, etc). This was just a quick look and may well be meaningless. However the results were as I would expect: springs get stiffer when compressed, and levers and pivots add friction which increases force when compressing and reduces force when extending.

As to whether any of this means anything in real life in this application, I have no idea. The belt seems to stay tight and bad things don't happen very often, so I am sure it is fine.

j.kenzie@sbcglobal.net

Thanks, Jim.

PorKen

Hard to believe but I do have other commitments besides reading Rennlist all day, every day.

I thought you were out of this thread? Which was good, because you just keep saying dumb things.

I answered your questions on page 15, BTW.

Would you like some cheese with that whine?

The roller and lever are not meant to be greased.


Note the tensioner/damper should be held vertically when compressing. Compress in steps, waiting for the T/D to 'reset' before compressing again. Temperature will affect the amount of effort required to compress and the length of time before 'reseting' (cold more/longer).

PorKen

Thought about it, but there was not enough of a market to justify the cost to make (and warehouse) 'specials'.

Those three flange head bolts have a lot of clamping force but you could always 'shim' the opposite side of one of the bolt holes with something.

As I have said many times before (to GB) tension is a symptom of the stock system, measured statically. Once running, with either system, the engine determines the actual tension level by the pull of the crank against the cams and pumps. As this pull varies with conditions so will the actual tension level.

With the stock tensioner, the belt must be pre-stretched to a great enough degree so that it will not get too long in most situations. Once running (and warm) the tensioner does exactly zero to manage the belt, the tensioner pulley never moves. In more extreme conditions the belt is flying around 'like a rubber band' and is kept mostly in place by the guide rollers. (Folks with an emotional investment in the stock system keep saying that I'm knocking it. I am merely describing what it is, and is not.)

With modern tensioner/dampers like the Audi it is all about maximum belt wrap on the crank gear, not static tension. This is less stressful to the belt and the engine, but it has to be perfect all the time. That is why the parts are so robust. (That Yuge pulley bearing for example.) It could be that this T/D was near/at the limit of its travel so it could not react to any further change in belt length but it appears there is still enough belt wrap to be effective so I believe there must be additional factor(s) involved.

Imo000

Shim it with something?!?! That's your solution to this problem? Making a hole bigger and then shimming it to keep the bolt in a specific direction is not as simple as showing something behind the bolt. Also, the clamping area of the bolt head is now less because of the enlarged hole. This is not a concern?

As for the belt flopping with the OE system. Why is this a problem for you? It makes no difference in the function of the OE system. The additional rollers are there to take care of this if, the flop is excessive. What the belt does under the cover is irrelevant as long as it's doing what is designed for. And it does this really well.

I understand your commitments outside of RL but when the $hit hits the fan you really should be on top of things and not hide behind these other commitments........at least I wouldn't .

ptuomov

The problem with the stock tensioner system is that in order for it to keep the belt wrapped around the gears in the worst case geometry change scenario it needs so much extension and pre-tension that in the other end of the geometry change scenarios the belt is over tensioned and wears out cam gears, breaks cams, snaps belts, and seizes water pumps. Although the stupid warning light in the stock system combined with bad choices by people is responsible for many of the catastrophic failures, it's still the case that even when maintained exactly optimally the stock system wears out expensive components and requires frequent replacement of parts (or risking catastrophic failure). The reputation of the 928 engine timing belt system as the Achilles's heel of the car didn't just appear from thin air.

I think you are correct about improving the PKT-B instructions. There should be instructions about what exactly to do if the tensioner extension is not within the tolerance range. How much can the bracket be adjusted and how should it be done? I'm sure that Ken will respond to honest and constructive criticism, in contrast to just spreading FUD or calling his product names.

Considering the forces acting on this tensioner system and taking a look at the hardware (http://liftbars.com/docs/PKT-B_bolts.pdf), I think that if the tensioner is not pegging at the minimum extension it will be very hard for the braket or fasteners to break. Just my opinion.