PorKen

Landseer

http://ingeb.org/spiritua/comebyhe.mid

Imo000

Have you measured the tightness of the timing belt when the piston retracts 2mm?

PorKen

Upper end of the Kempf tool window.

Landseer

Good-to-go.

H2

That's perfect, PorKen. I've compared three different Kempf tools to two different 9201 Porsche tension tools (with calibration bars) and the 5.2 tension setting is at the top of the window on the Kempf tool. The Kempf tool was made for the earlier 928s but the middle of the window setting works OK for all 928s (but it's not 5.0 in the middle of the window!). I use the Kempf tool for quick checks and the expensive (and more difficult to use) Porsche tension checking tool for my spring checkup.

I also have a 968 with the stock Porsche auto tensioner and it's a great addition to the Porsche. I'm still not convinced that Porsche did the right thing by not putting the auto-tensioner on the 928 also and phasing out the primitive design. I guess they had already seen the handwriting on the wall and were planning to phase out the 928 anyway and didn't want to throw more money at a redesign/retrofit? The old system did/does work if you stay on top of the settings and keep all your rollers and T-belt in excellent shape. But, as can be seen by many posts over the years on Rennlist, the stock design isn't foolproof.

My point is that the PorKen tool tension setting is "right on."

H2

worf928

I really hate to play the part of the Etiquette ****. This was a good thread a few pages ago. I would like to be able to be able to read (and perhaps ask questions) in the context of a technical interchange and to better understand the dynamics of what's going on under the belt covers. Name-calling and linguistic spear chucking just makes folks tune out.

worf928

No design is foolproof. The universe always grows a better fool.

I am actually in both camps in this debate. While I have about 2.5% of Greg B's timing belt collection, I do have a modestly-sizable collection. I agree with him that the stock system - when done properly and methodically - works just fine. The belt system causes problems with it is not touched in a proper and methodical way (modulo our current rebuilt water pump problem that is independent of the guy installing it.) I've seen enough of both kinds of work to satisfy myself on this score.

On the flip side, much of what Porken relates I agree with too. The 928's belt system - even when working as originally designed - allows a lot of belt flapping while systems designed afterward don't.

This debate is getting too-close to "religious war" status though.

James Bailey

I for one would NEVER use an aftermarket system designed on the "it sorta looks like it should fit" but eliminates the belt tension warning system (flawed as it it it is it is better than NOTHING ). I frankly see little wrong with the stock set up and little need to try to fix it . There will be issues with anything mechanical and failures will happen. We just do not know what those might be. But what do I know the old very brown 1980 I NEVER did the belt , NEVER checked IT , NEVER even LOOKED at it. I had it over 8 years before the who knows how old timing belt stripped a few teeth at Willow Springs came off the track after powering through turn 8 at about 6,000 rpms pulled into the pits it went to idle and it stopped running ....tried cranking but it was spinning too fast ...I knew it had jumped time... so towed it back to 928 International threw on a belt and was good to go again. Yea that old system sucks ! The "problems" with the stock setup are more an issue of who worked on them than anything else. I got so many calls from shops who thought the tensioners were pressure fed and had " collapsed" and wanted to buy replacements. Here we have a POSSIBLE solution to a largely none existent problem. Fact is the Porsche system works pretty darn well and has MILLIONS and MILLIONS of miles to prove it.

dprantl

Can anyone show me an example of a car designed in the last 20 years that has a belt tensioner system from the factory like the 928? If it really is a good design, how come it doesn't exist in any other car? Just because the 928 system works doesn't mean it is not badly designed and cannot be improved upon. There are many engines in that 20 year window that are similar to a 928 engine. Mercedes used vacuum door locks until the end of the '80's. Was it good, no! Did it work, sure did. Could it be improved upon, you bet! Porken's tensioner system is not something that he designed from scratch. Like was said before, this system is only slightly adapted from a factory design of another make for a very similar engine.

Dan
'91 928GT S/C 475hp/460lb.ft

F451

Would have been a different story if you had a 32v when your belt went would it not have been?

Not disputing what you've stated, but I don't see the relevance of your example of a belt failure on a 16v car that you admit you did zero belt maintenance on, never even looked at the belt.

Interesting thread besides the mud slinging, but it happens.

James Bailey

my point was even when badly neglected ignored and raced for many years it worked rather well and yes if it was a 32 valve i would have looked at it sooner. I just wondered how long it would run ! Also figured I would knock out the rod bearings long before the belt failed i

Landseer

Instructional would be high-speed (slow motion) video taken of the belt, and also of the tensioner responses.

Its used often in diagnosis of conversion issues on consumer goods packaging equipment.

Would be perfect here.

jcorenman

Ken, I am a big fan of your tensioner design, and I fit a PKsn'r to both of our 928's when it came time for t-belts. And the V32'r is brilliant, and a great time-saver. But that doesn't mean that I think the factory design is bad. It works, and works well-- and you know as well as I do that a "better" design doesn't make the previous effort a "bad" design. It's more like "good" and "gooder"...

And Greg B. and Mike (DanglerB) are absolutely right when they point out that the PKsn'r has a limited history, and may have failure modes that are yet unknown. I don't think that is the case, and feel strongly enough-- based on 40 years of engineering experience-- to bet our motors on that. But that same experience also tells me that nothing is 100% certain, and stuff happens that cannot be anticipated. So I watch carefully. And I also think that those who want to wait, and watch, also made the right decision. Because there is no "wrong" answer, only multiple "right" ones.

So please, show those who disagree with you the respect that they deserve.

Thanks.

JHowell37

For the first 45K miles I used the factory system that I rebuilt when I first got the car. A little over two years ago, I got one from PorKen which I believe was from the second production run. I didn't have any real issues with the factory tensioner. Here are my observations with the factory tensioner.

1. The factory tensioner leaks.
2. Factory tensioner uses a lot of parts.
3. Although it's not unreliable, its design clearly violates the KISS principle.
4. I know of no other car that uses such a complex mechanism.
5. The shoulder bolt can be easily bent, most likely caused by excessive belt tension, and it relies on plastic bushings that are of dubious quality.
6. The factory tensioner is bulky, and takes up a lot of space.

Here are my thoughts on PorKen's solution.
1. Simplicity.
2. Clean. No oil leaks.
3. Audi/VW roller is much sturdier then the factory roller.
4. No more taking arbitrary measurements that may or may not be correct.
5. "Rebuild" requires 3 commonly available parts.
6. Less bulky. Allows much easier access to air pump.
7. No more belt tension light when you least expect it.

Several people have mentioned the belt tension light, and that they are happy that the 928 has one. I have to agree with PorKen on this one. This warning light is Porsche's vote of "no confidence" in their system, especially when you factor in the 3-minute delay. To my knowledge, NO other production car has this warning system. Ironically, NO other production car uses this exceedingly complex tension system either.

My final thoughts. You should not have to check your timing belt every 10-15K miles. Don't say anything. You shouldn't have to do it. That's the kind of bull**** that brought Porsche to its knees 15 years ago. Some people can't justify making the change and that's fine. I can't imagine ever taking a step back.