kmascotto

Interesting...thank you for sharing. Is this the one you are referring to?

http://forums.vwvortex.com/showthrea...er-failure-AHA

But this may not be as common as indicated. These things get blown out of proportion...

I do like the idea of a warning light...

jcorenman

Indeed, our GT had 75K on a PKT (with two belts) before I swapped back to a factory tensioner. It didn't fail, I just lost confidence in it and came to appreciate the importance of the alarm circuit.

PorKen

I can certainly use the old bracket, if you want to sell it. (PM or email, if yes.)

I've had one idea for a possible mechanism, but no one has tried it, to my knowledge.

https://rennlist.com/forums/928-foru...ing-light.html

gcthree

This is why I went with rebuilding the stock tensioner on my '89; not having that light was a big issue in my mind.

kmascotto

I'm going to stick with mine too. Its a simple system...that works.

davek9

The old static system imo causes more issues than a constant dynamic system will, if it was/is a better belt tensioner then why isn't it being used on belt systems today?
Porsche added all those extra guide pulleys to compensate for it's weaknesses, and added the light too
The stock detensionre does work at compensating for engine expansion, but not belt dampening. It is also very maintenance heavy, most don't do what is required to keep it working correctly, add rebuilt after market water pumps to the mix and you really do need a warning light

Just saying from the ones I've seen that have been neglected.
Example: see the pics I posted, this should have never reached this point, the PO didn't do what is required.

kmascotto

imo "the best system", is the system it was designed for... The whole concept of bolt it on..."and forget it" is bad. Most of us know maintenance is key and those who don't...pay the price.

jcorenman

To your last point, agreed- it was neglected and should never have reached that point.

But neglect happens, and it is certainly not prevented by a different choice of tensioner assembly, particularly one billed as "automatic". Defective parts happen, as well. In this case you have a relatively simple repair, but if there had been no warning then you would be pulling cylinder heads.

Calling the factory tensioner a "detensioner" misstates its fundamental purpose: To compensate for thermal expansion and maintain a constant tension.

There are two ways to maintain belt tension: manually with an adjustment, or automatically with a spring. Porsche's system is actually quite clever, and allows a fixed adjustment to maintain constant tension over a wide temperature range. This, in turn, allows a meaningful alarm circuit to be fitted. Once the adjustment is set, any change in belt tension signals a change in the belt geometry, and a change in belt geometry is always bad.

Automatic tensioners use springs for tension. Springs are subject to oscillation and need damping-- either friction or hydraulic. The Audi/NTN auto-tensioner uses hydraulically damping, a check-valve which allows it to quickly take up any slack and tighten the belt. This is a one-way action, it can loosen the belt only very slowly.

The advantage of an auto-tensioner is convenience: Install it, pull the pin, and you are done-- free to forget about it for another 60K miles. I don't see the advantage, personally.

P.S. As to why no one used the Porsche system, it might be that they had a patent or two: US 4,151,756 and US 4,573,952

davek9

Thanks Jim points well taken

Dave

123quattro

I wouldn't hesitate to run the VAG tensioner. I have one on my 928S and my engine is very interference. It's a maintenance item. You replace it every 80k. There are no issues with them on Audis. This is the same tensioner that they also run on the belt drive 3.6/4.2 V8s. Nearly everthing they made from the early 90s through mid 2000s uses this part. They don't fail.

Imo000

What do you mean they don't fail? Run a Google search and it's littered with failed Audi tensioners. They fail just like every other hydraulic/spring loaded tensioner out there. Many other manufacturers use them, not just Audi. Ken happened to use the Audi unit but similar designs are used in countless other cars. They are very popular but the design doesn't allow to have a warning system. It's something that the manufacturers accepted as a design flaw, just like Porsche did with the the 911 (they accepted the engine being in the worst possible spot).

mazdaverx7

Talk about the luckiest 928 owner of the month! Glad he shut the engine off instantly!!

123quattro

I've owned 3 Audis that use this tensioner and have it on my 84S. I also spend a lot of time on Audi forums. I've never heard or know anyone that has failed one. I do however know a lot of people on here that have issues with the factory 928 belt tensioner. To each their own.

Imo000

All those issues are not with the tensioner (maybe a couple are) but with something else in the timing belt system. The tesioner if kept in shape, and it can take a lot of abuse, is very robust. I don't remember reading a single case where the tensioner failed and cause a major faliure. The tensioner roller is noit part of thner. Maybe someone can remember a case or two but I sure can't.

PorKen

Out of millions of tensioner/dampers, some will fail, especially if not maintained.

You don't see millions of posts about how good something is when it works.