jcorenman

If "unproblematic" means that we didn't trash the engine in the middle of east-jesusville, then you are correct on that point.

Not in my experience. Compression marks, yes, but not a ridge of plowed gasket material around the edge of the boss. And why is removing the gasket a good idea? That won't stop the bracket from moving under the fasteners, it just gets rid of any "witness".

I don't think we still have any idea what happened here. There's been a lot of possible theories, and certainly brackets moving around on fasteners could be a contributing factor.

Something else that is possibly related: My "unproblematic" bracket had an incorrect countersink but the thru-hole was drilled to 8mm, a tight fit on the M8 flat-head fastener-- almost "dowel-like". Later brackets are all drilled oversized to 9mm, correct? So all three corners have the potential to "float", where on mine the fastener closest to the tensioner itself was precisely fixed.

Sure, good idea. What do you have for facts?

Here's what has been "discovered" so far: The timing jumped 8 teeth on a cold-engine sartup, it had a PKT and a racing belt, and three of the four gears were new. We also know that the rod extension was 9mm cold, which is right at the top of your acceptable range.

j.kenzie@sbcglobal.net

Hi Jim,
Removing the gasket might eliminate gradual crushing which might lead to fastener looseness.
Dave

Lizard928

The thermal expansion rate between the two farthest holes on the bracket, lets just say is 4" roughly. At 4" the thermal expansion rate difference between the two materials is according to my math (could be wrong here, it's been awhile), over a 100C temp change is .0004". Not really enough to worry or even think about. If we are really worries about that, then look at the steel exhaust manifolds bolted to the aluminium head over a much larger surface, with a much larger temperature variation. They are not commonly blowing out seals. Newer cars have a very very think steel plate which is the gasket, they don't have higher failure rates on average.

I am afraid Jim those ridge marks you see on your gasket, I have seen on stock tensioners as well.

Also, yes it has jumped teeth. But we cannot blame that on the tensioner. Let us say for a minute that the WP was bad out of the box, and it caused the tension to be released. The stock tensioner would have had the same thing happen if not even sooner than the porkensioner. Greg has stated he has seen a reverse rotation cause the belt to skip with a stock tensioner. So yes, the skip did happen with his tensioner on the car. But that does not directly state that the tensioning system is at fault as I read your implication to be.

Lets get back to either a) finding out exactly what caused the problem in the first place, or b) move on to fixing it.

Imo000

If the tensioner let the belt skip, then it IS the fault of the tensioner!!! The job of the tensioner is to keep the belt tight, it it doesn't then the tensioner system as a whole failed. What happened to the OP is a faliure of the tensioner to keep the belt tight. I would start by redesigning this system so it can be more versatile to variations in used 928 engines. It's clear that the rage this tensioner operates is inadequate. Enlarging the holes by the customer IS NOT and acceptable solution.

PorKen

Let me know if/when more information becomes available.

Otherwise, I have things to do this week(end).

Ciao!

jcorenman

Actually 4 thou, not four tenths. The linear coefficient for aluminum is 23, steel is 12 (units are 10^-6 per deg C), so for delta-T of 100C over 4" would be around 0.004 or 0.1mm. Still small, enough to worry about?

Hai asked a reasonable question: What should he check or measure when he disassembles the PKT bracket? Ken apparently doesn't have anything, I can make a couple of suggestions.

First, I think it would be good to know how tight the fasteners are. So maybe use an indicating torque wrench when loosening them. Also, before removing the plate altogether, I would loosen or remove the fasteners one at a time and find out where each bolt is sitting in the oversized hole, then reinstall it so things don't move and check the next. My biggest concern is the countersunk fastener, by its nature it needs to be centered (which is why I don't understand the change to an oversized hole).

It would also be very helpful to have some hi-res pictures of the gasket (if fitted), and the flathead fastener and countersunk hole, and also where the lever bears on the roller pin. With low miles there shouldn't be much wear.

Charley B

I have to say, watching my heroes (Greg, Jim C., Colin, Ken etc. ) arguing is a little like watching your parents fighting. Highly entertaining and informative but yet not a little disconcerting. You know, that uneasy feeling that someone might take it a step too far at any moment.

marine928

With everything Hal replaced, 9mm extension should have been a cause for some concern, and warranted a little investigation. Being at the high end of tolerance is troubling especially knowing that some wear is going to occur in the future.
Before installing my PKT two years ago, I did a lot of research on Audi tensioners utilizing the Audi owners forum. I also looked at similar tensioners on other cars. My conclusion was that Ken's Audi product had sufficient history under various situations and applications to go with it.
Kinda like the PK clamp to limit front and back migration of TT, PK lift bar, Constantine's torque tube mods, using bolts on my auto converter to replace the poor design welds that break and rattle, VW lamps in the headliner and rear hatch, ( LED's) Greg's fuel lines, custom modern transmission lines, alternator upgrade, upgraded brain( not mine, the 928's).
Porsche built a great car, but like anything else, there is always room for improvement. We all drive better cars due to the efforts of guys on both sides of the isle in this issue. Not to mention issues with the five speed gear boxes.
Got to get some more popcorn and root beer.

Imo000

What more information do you need before announcing what happened ? Of has this been marked off as a "this will never happen again" in you books?

ROG100

When the idea of a Racing belt was originally brought up it was assumed - "incorrectly" - by a number of people - myself included - that the belt used Kevlar.

Once the process of production was instigated Gates issued the make up of the belt - which did not include Kevlar. That was a long time ago.

I think I posted the exact make up in a power point slide in this thread so why do we still think it is made of Kevlar?

ROG100

If you have all the detailed facts could you please state them again as I obviously missed them.
Sorry if you already did this - just give me the post number?

GregBBRD

Well, I just spent an entire day reflecting on this whole Portensioner thing.....Racing belts, stretchy aftermarket belts, no lower roller, one tensioner for two completely different belt tension requirements, steel bracket on silicon aluminum block, reaming out holes to compensate for design, spending extra time and money setting the cam timing....never really knowing where the cam timing will be at when running, only being able to use this tensioner system with brand new gears, not being able to use it with surfaced heads....the list goes on and on.

And I realized how stupid I've been.

My sincere apologies to all those people I've offended by trying to apply logic to this topic.

This entire Portensioner has absolutely nothing to do with me....absolutely nothing.

I've got zero financial stake in this subject.

I've got nothing at personal risk.

What people decide to do with their own cars has no impact on me or anything I do.

I will continue to do what works for me and simply smile with the satisfaction of having made the correct choice, everytime someone turns another engine into trash....and that is inevitable!

The only parting advice I have....figure out who has a financial stake in this product and consider their advice, from that perspective.

As the Knight guarding the Holy Grail said to Indiana Jones:

"Choose wisely."

Lizard928

I just double checked, and yup, my math was off. My apologies.

It is not enough to worry about in my books though. The exhaust manifolds have much greater movement as does the starter bracket on the later engines.

as stated none of the brackets I have pulled off have shown the standard "shuffle" marks from an excessive movement between it and the block. I have not had to remove any black edition brackets yet though, so I cannot comment there.

Imo000

That's Ken's job.

Lizard928

How is it Ken's job? It has yet to be 100% determined what caused the failure.

If the failure is caused by the engine being spun backwards which the factory specifically states NOT to do, how can Ken be held accountable for that? Greg has stated that he had an engine with a factory tensioner skip teeth when spun backwards. So if a factory unit can allow it to happen, how is it that Ken is magically supposed to design a system that allows the engine to spin backwards when it was never designed to do so?

Is his system 100% failure proof, NO. Is any system going to be? Not a chance.
As end users, do your own research on the systems and options out there, and make your own choices.