PorKen

Let's leave your prison fantasies out of this, shall we?

"You look mighty cute in them jeans!"

Have YOU studied the stock tensioner? What it does. Or more specifically, what it doesn't do?

Perhaps you can answer the questions I posed to your apologist-second-in-command, above?

If you are talking about playing an active role when the engine is turning, besides (allegedly) indirectly collapsing when warm, you would be correct.

The stock tensioner does NOTHING when a hot engine is turning. Belt pre-tension only controls how much the belt WILL flap. The more load placed on it, the more it WILL flap.

PorKen

Interesting thought.

It would also make sense that with a Racing belt one would reduce the pretension with a stock tensioner as the Racing belt does not stretch as much.

GregBBRD

Amazingly, internal conbustion engines do have a tendency to stop a large percentage of time in the same position. I know that doesn't seem logical....one would think it would be completely random....however, studying ring gears tells engineers that this is not true.....a given engine is going to stop in the exact same position a huge percentage of the time.

Where the cam belt is loose and where the belt is tight is going to be completely dependent on where the camshaft preload is pointing when the engine comes to rest. On your engine, it might be on the "loose" side of the cam belt and the Audi tensioner might take up the slack....most of the time.

To do a "complete" experiment, you'd have to repeat this experiment multiple times, in order to get the engine to shut down in a position where the camshaft preload is in a non-beneficial position for the tensioner.

Make sense?

GregBBRD

You need to go back, start at the beginning, and read what this thread is about.

Regardless of what you say or think, reardless of what you think I know or don't know....regardless of what kind of wise cracks you want to dream up....the OP has a ruined engine with a Gates racing belt and your tensioner.

Nothing ran through the belt, new gears, heads not shaved....everything perfect.

That's the reality!

And what you need to figure out is:

WHY?

PorKen

Objection. Assumes facts not in evidence. The only known FACT in that statement is 'new gears'.

Something may have run through the belt. Heads were not measured with any precision. Large repair bill suggests it was done. Shaved heads is the most likely reason why the T/D was installed (and run) out-of-spec or near to it.


I explained this, above. Please read before regurgitating.

After you have finished reading, why don't you go measure your Bellevilles?

the flyin' scotsman

makes sense Greg that my engine may stop at different points and perhaps produce different or similar results.
Im sufficiently satisfied today I'll put the cover back on, drive the car further and then repeat the process but given its snowing (joys of springtime in Canada) my next report might not be for a week or so.

edit: Before refitting the the DS T.belt cover I turned the engine a little with the starter; the previously noted slack between the WP and cam gear was gone. Cam gear to OP remained same as before.

ptuomov

That does make sense.

There are some number of camshaft angles at which the valve springs are in local minimum energy position. Engine wants stop at those angles. [Edit: There's also the cylinder pressure/vacuum that favors certain crank angles. The gas in the cylinders acts like another spring if the valves are closed. The crankshaft of a V8 wants to stop at a crank angle that has one cylinder at 45 degrees BTDC in a compression stroke and one cylinder 45 degrees ATDC in power stroke (with unburned air). I haven't computed at what camshaft angles does the engine want to stop from the valve spring perspective.] Sometimes those angles may be such that the valve springs pull a tension to the belt between the cam gears on the water pump side. Sometimes those angles may be such that they pull a tension between the cam gears on the crank gear side. This is with both the stock belt tensioner and with the Audi tensioner.

With the stock tensioner system, I think one needs a higher pre-tension on the belt if using stiffer valve springs. For the same reason, the 32-valve engine also needs a higher pre-tension on the belt than the 16-valve engine if the stock tensioner is used.

With the Audi tensioner, by my logic, you don't want to install the tensioner to be too far extended. Doing so allows for too much slack in some crank angles on the water pump side. Without too far extended tensioner, the valve springs can't pull too much slack between the cam gears for the belt to skip. That's why in my opinion it's important to install the Audi tensioner to have the right amount of extension.

By my logic, there's no big difference between the stock belt and racing belt, whether with the stock tensioner or the Audi tensioner. On the one hand, the racing belt is stiffer so it's a little more sensitive to the stock tensioner responding to thermal expansion of the block the right way. On the other hand, if the racing belt stretches less (don't know that for sure) then its going to make the stock tensioner system a little more accurate than with a stretchy belt. That's why Roger's advice to install the racing belt at the same tension as the stock belt makes perfect sense to me, as long as the valve springs are also stock. My logic, while surely not perfect, is consistent with what those Gates engineers are saying.

It's my opinion (not a fact) that the Audi tensioner system is better than the stock tensioner system if it's installed not too far extended. Neither system is perfect, but the Audi tensioner is going to wear the other related components a lot less by my logic than the stock tensioner. An opinion, not a fact.

Lizard928

Has anyone besides me rotated the engine backwards with a porkensioner installed?
I did and no teeth were skipped (without idler below crank gear), even if I did it quickly.

My prior question hasn't been addressed. Please hook up a dial indicator and measure for play in the waterpump bearing. The belt position on the 1-4 cam gear is not normal and can only really be caused by a bad waterpump from my experience.

Has the porkensioner been removed and all pieces been inspected for proper mounting?

Hai gebissen

At this point, it is necessary for me to make it clear that I am not blaming Ken or his tensioner, Roger, Gates, or anybody else for this failure...except myself.

As far as I know, I installed the new cam gears (Roger), water pump (Porsche) and oil pump gear (Porsche) correctly. Nothing broke and no bolts are loose.

I installed the Porkensioner and Gates racing belt sold to me by Roger according to the instructions provided with the tensioner.

However, the instructions and Ken here on this very forum both stated that the maximum allowable tensioner extension is 7mm. Upon installation, and after turning the engine over by hand and with the starter, I observed 9mm of extension. At this point, for whatever reason, I failed to take Ken's advice and modify the tensioner to reduce this extension to 7mm. I still do not know why it was extended 9mm (10mm measured after failure). I don't remember if I was aware that 11mm was maximum extension.

Bottom line...I did not follow instructions, and this, perhaps aggravated by my removal of the crank gear idlers, lack of new crank gear, and use of the racing belt, resulted in my failure.

Lizard: I agree that the belt position on the 1-4 cam gear is odd relative to the 5-8 position. I can measure the water pump as you described next time I am at the car (Tuesday).

GregBBRD

My opinion has always been the same...from the very first day.

If Porsche had gone back and engineered a new hydraulic tensioner system, for these engines, they would have engineered a tensioner (actually a pair of tensioners....one for the early engine and one for the later engines) that was suitable for the job....not plucked an Audi part off the shelf and assumed it good enough. (Ken brought up the 968 tensioner....have any of you had one of these in your hands? Has anyone here tired to return one? Because I have....and there is no stinking way you are ever (no matter how big you are) going to return one of these, by hand, with an 8mm allen socket! There's simply no stinking way!!!!

Porsche would have run these engines hot. cold, and everywhere in between, and then measured exactly what was needed to control the belt.....in all situations.

They would have done this, Tuomo would have done this, Colin would have done this, Corenman would have done this, I would have done this.

Ken...not so much.

Porsche would know, for sure, if the lower rollers were needed and what they were needed for....Ken just arbitrarily thought it was a good idea to remove them.....with only a theory of why they were put there. (What happens if they were put there to prevent something freaky that happened every 10,000 engine startups? What heppens if they were put there to keep the belt from skipping when the engine is turned over with a low battery and the compression pushes the pistons backwards when it doesn't start? Or if they were there in case the engine backfired. Ot if they were put there to keep the belt from slipping when the slack "gathered" on the oil pump side of the belt? Who knows, for sure?)

Ken did none of this....no measuring of actual tension forces on the belt...either stock or with his system....screw hot or cold....he measured nothing....by his own admission. Zero quantitative data.

Ken saying: "Here's something that I cobbled up in my garage, that looks like it should work"...doesn't make it perfect.

And it sure isn't engineering, people.

Lizard928

Thank you.

PorKen

And no one will convince you otherwise. You don't even realize that the nonsense you talk about is in terminology that I created over the years.

This thread, while unfortunate for the OP, who I feel bad for, has conceptually nailed the lid on the stock tensioner. The one final puzzle was the change in tension for the 32V which became clear a few posts back. You still will not have understood it, but, in a few years you might talk about it, unwittingly.

jcorenman

Hai, I am sorry that this thread got sidetracked into theology, but it is important to understand what happened. No one deserves a trashed engine for simply hitting the starter.

Ken, every technical discussion regarding your designs does not need to devolve into name-calling. I've been engineering stuff and getting paid for it for 50 years now, I am not an "apologist" for anyone. If you think my analysis is wrong then comment on that, but this has nothing to do with the stock tensioner. Stop deflecting.

The "facts" are that the belt jumped a bunch of teeth as the result of trying to start the engine with a weak battery. I think we can agree that the belt can only jump teeth as the result of a loss of tension, and the device controlling tension was your design. Why not try to help solve it instead of insulting folks and deflecting attention elsewhere?

I agree that my theory is just a theory, and may not explain what happened. But I don't think your theory is any good either: If the tensioner was at 10mm cold after the mishap then it was not maxed out. Even if it was at 11mm, there would still be no appreciable slack in the belt-- not enough to jump teeth.

To have enough slack in the belt to physically be able to jump teeth, wouldn't the tensioner need to be compressed most of its travel? How is that possible?

docmirror

I don't think trashing the stock tensioner system is warranted, or justified. I've never heard of a tensioner failure on a stock unit even when they are let go without oil, or without adjustment. They seem amazingly robust to me, and when set and maintained by a competent wrench, will provide 40k miles of good service.

This is not a slam on the newer style tensioner, with the more modern design, but to bash the stock tensioner with no failure data is disingenuous.

Has the OP strung a stock non-racing belt on the existing gears? If not, that would be the next useful test, and see what the tensioner deflection is. After that, compare the old belt to the new belt with couple of pipes and string the belts around them. Something has to add up here to 9-10mm deflection and it's important to know the data from these tests.

worf928

Yup. I've seen some damn sorry belt systems - thanks to the previous technician - with the stock tensioner. About the only way to kill an engine with it is to tighten it down as much as possible and even then you can loose a bunch of teeth from the belt.

Yup. Too much theory. Not enough diagnosis. Too much name calling. Let the OP gather some data and report back.