PorKen

If the heads have been (re)machined, you should consider upgrading to a PKT-S bracket which fits a larger range of engines (with the trade of a few more installation steps). Or, I shudder to say, return to stock, if out of range.

(Upgrade with core return, here.)

PorKen

From your symptoms, could it be that the (plastic) impeller has spun on the shaft? It may be pumping marginally until the engine is rev'ed up again.

85euro928

Subsequent to changing the tstat the system functions correctly, however the WP still make noise.

GregBBRD

You are missing or ignoring my point.

If someone installs your tensioner and has 2mm of extension on a cold engine (2mm from Audi tensioner being bottomed out), once the engine gets hot, the Audi tensioner can (will) become completely bottomed out. (You claim that there is 3mm-4mm of travel difference between hot and cold with your tensioning system.)

Once the Audi tensioner is completely bottomed out, there is no longer any "give" in the system and the only possible result is for the belt tension to go very high. (For a reference point, 2mm additional tension on a stock tensioner will raise the belt tension from 5.0 to 7.5 units (using the 9201 Factory measuring tool).....and that is with the "spring discs" collapsing some to "absorb" some of the additional tension.

With your system, once the Audi tensioner is bottomed out, the actual belt tension will go extremely high and the resulting load on the water pump will also be very high.

Because the stock tensioner has a huge adjustment range and the internal "spring discs" always have give (that's why they are there), this can never happen in the stock application.

KenRudd

PorKen

As usual your preconceptions are faulty, your 'facts' are incorrect, and the 'theory' you are trying to present would not apply to the case in this thread anyway (the heads were machined ).

Just like you assume the oil does something, you assume the tensioner washers have spring in them, but you have never measured the actual range or determined whether it is in-fact enough to compensate for heat expansion of the engine. When cold the washers may have some give, but you don't know how much. When hot they flatten out, making the tensioner fixed.

I measured a stock Belleville stack (thread below). Cold and warm. The stack's effective range is nothing to write home about and that was without pre-flattening the malleable washers with the force of the belt being over-tensioned to the stock 32V spec.

https://rennlist.com/forums/928-foru...l#post14436133

You really should actually KNOW these things yourself if you are going to talk about timing belt management or valve timing or anything that (thankfully fewer and fewer) people mistakenly ASSUME you know about.

GregBBRD

Instead of your steady output of personal attacks and innuendos, why don't you address the simple math and physics of what I'm saying....

Here's the simplest way I can state what happens:

2mm extention cold. This will result in the Audi tensioner being completely bottomed out, when engine is hot. Once the Audi tensioner reaches its internal stop (bottomed out), there is no other place, in your system, for the increased belt tension to be reduced (absorbed) and the belt tension sky rockets....putting excessive load on the water pump/other components.

BTW....the humor of you just now (10 years after "designing" a replacement tensioning device) testing and seeing how the stock tensioner works is absolutely fantastic!

We're laughing our a$$es off!

And as a point of order, many people install the replacement "thicker" head gaskets when the heads get shaved. If they don't take .3mm or more off of the heads, this thicker head gasket will move the heads father away from the crankshaft. (This will result in your tensioner system being even closer to being bottomed out.)

GlenL

Ken,

Did you do the analysis as to whether this adjustment would maintain belt tension?

Billions of miles later, it's clear that the problems with the stock tensioner are due to mechanics (and "mechanics") who don't do the maintenance correctly. And you sell your kit to home mechanics with uncertain abilities.

One thing's for sure: that warning light will never come on again. Someone should sell a kit just for that.

One more thing: I've got more faith in Porsche engineers than in an enthusiastic amateur.

buccicone

AO

crushingday

hlee96

Wouldn't the best test is to have Thom return everything to stock and a Laso pump and see if he will need another premature WP replacement?

GregBBRD

Water pumps do fail....and the OP might just be really unlucky and have had four pumps go bad.

However, the OP's very first statement is "I need some advice".

And there are known "issues" with the aftermarket tensioner he has been using....depending on which "version" he has determines the potential risk. Some problems have been "solved" by the multiple versions of brackets that have been made (four different brackets, to date.) Some of the problems were solved by the multiple hardware changes (too many to count.)

But there are still known problems....and it is possible that he has been experiencing one of these problems.

The choice: Let him continue to "suffer" through changing infinite quantities of water pumps or point out the potential problem/problems?

And this particular potenial problem is very basic and simple to understand:

2mm less 3mm to 4mm = Less than zero. And in this particular belt tensioning system, less than zero means that the actual belt tension goes up in a huge amount and all the pieces the belt touches (and the belt) are going to suffer.

Is this his particular problem?

I have no idea.

But he asked for advice....and ignoring this known problem (made considerably worse by the "current" bracket) is very much like ignoring the proverbial elephant in the room.

Stock belt. Stock tensioner. Stock water pump. Keep it simple and reliable, drive it for 45,000-60,000 miles!

PorKen

What's really funny, or really sad if you think about it, is that I had to measure what you and all the others who have been parroting the myth that the stock tensioner has some spring in it, effective damping, and/or even has a reasonable range of movement to mimic engine expansion. Despite (formerly) being considered an expert on all things 928, you have been both intellectually and physically lazy to actually prove that these things (and others) actually happen.

It's quite clear to me (and most others reading), what you fail or don't care to understand, you assume that Porsche knew what they were doing.

You must be talking about some other 'aftermarket tensioner' because your statements are not accurate vis-a-vis the PKT. All this has been discussed previously.

At one time (in your ongoing irrational campaign against my products) you complained that the PKT could not work because it wasn't tight enough. Obviously, for the thousands of folks running PKTs, that was proven to be a figment of your imagination, also.

There is! And it works!

https://rennlist.com/forums/928-foru...-light-10.html

DKWalser

I find this form of argument interesting. None of us, individually or collectively, has a tenth of the engineering resources that were available to Porsche. Does that mean its not possible to improve a 928 beyond stock? Greg has designed several products that he claims improve on Porsche's original designs. See, for example, his oil filler neck baffle, his 928 windage tray, and his "Arizona A/C" upgrade. Are we to reject out of hand his claims that these products improve the 928 on the basis that it's not possible (or so implausible as to amount to the same thing) that a single person can improve on the work done by Porsche's brain trust?

Frankly, that's a ridiculous argument. Experience has taught us that 928's can have oiling issues and that the stock A/C system is inadequate for hot climates. So, as good as they were, Porsche's engineers were clearly failable. Once we acknowledge that, what's the point of trying to slam Ken (or Greg, or ...) for trying to improve on the work of Porsche's sainted engineers? Porsche's design of the 928 wasn't revealed to its engineers by God on Mt. Sinai.

Note: I'm NOT taking a side in this argument between Ken and Greg. You either find Ken's arguments persuasive or you don't. You either find Greg's arguments persuasive or you don't. But the persuasiveness of their arguments should come from the merits, not from an appeal to the authority of engineers who have not weighed in on the argument.