Timing Belt / Tensioner Recommendation
01-04-2010, 03:32 AM
#76
Former Vendor
Porken:
In my humble opinion....you are being an arrogant (defined by Webster's as: exaggerating or disposed to exaggerate one's own worth or importance in an overbearing manner) ***.
It's not good enough for you to let me do things my way and you to do things your way and just walk away...you need to keep attacking. (I think everyone will consider your last sentence an arrogant attack.)
Clearly, the motion from your tensioner when the engine is cold, is the "backforce" pushing on your tensioner and this makes the belt loose. You, me, and everyone else here knows that the belt doesn't stretch enough to make your tensioner "move"....nice try. It certainly isn't getting tighter...everyone also knows that. That leaves only one thing....the belt is getting looser from the "backforce"....just like I said from the very beginning. Certainly, everyone here clearly sees that...no matter how hard you attack me, trying to divert attention away from the obvious.
If you took the time to think about my points, instead of trying to see how clever you can be making cute comebacks, you'd know that the Audi tensioner's ability to keep the belt tight is overcome by the leverage of the Porsche designed belt system. I'm sure that the Audi tensioner works great in its proper application. However, taking a piece from another vehicle and making an adaptor to make it fit on another rarely works. In this case, clearly the Audi tensioner's spring pressure is inadequate due to the leverage on the Porsche tensioner bearing. Of course, the tensioner could be engineered to have increased spring pressure, but then the timing belt on the 928 would then be too tight.
To make this tensioner work properly on the 928 engine, the tensioning bearing would need to be moved away from the crankshaft to reduce the leverage that the belt has on the roller....just like the Audi engineers did...and you did not.
And by the way....that belt that stretched was supplied, against my wishes, by Mark Anderson. You can bet that we never used anything but Factory Porsche belts on his engines ever again!
Look, I'm not going to further allow you to attack my credibiltiy, with cheap shots. Therefore, I refuse to discuss this matter any further with you in this forum.
And for those of you that don't understand the basic engineering problem here...simply try to remember that I have nothing to gain financially from this discussion. It has zero financial impact on me if you choose to use the factory pieces or Porken's thing. However, I will continue to use Porsche's method (regardless of how irresponsible that is), that has worked flawlessly for millions of miles.
Have fun guys...I'm out of this one.
In my humble opinion....you are being an arrogant (defined by Webster's as: exaggerating or disposed to exaggerate one's own worth or importance in an overbearing manner) ***.
It's not good enough for you to let me do things my way and you to do things your way and just walk away...you need to keep attacking. (I think everyone will consider your last sentence an arrogant attack.)
Clearly, the motion from your tensioner when the engine is cold, is the "backforce" pushing on your tensioner and this makes the belt loose. You, me, and everyone else here knows that the belt doesn't stretch enough to make your tensioner "move"....nice try. It certainly isn't getting tighter...everyone also knows that. That leaves only one thing....the belt is getting looser from the "backforce"....just like I said from the very beginning. Certainly, everyone here clearly sees that...no matter how hard you attack me, trying to divert attention away from the obvious.
If you took the time to think about my points, instead of trying to see how clever you can be making cute comebacks, you'd know that the Audi tensioner's ability to keep the belt tight is overcome by the leverage of the Porsche designed belt system. I'm sure that the Audi tensioner works great in its proper application. However, taking a piece from another vehicle and making an adaptor to make it fit on another rarely works. In this case, clearly the Audi tensioner's spring pressure is inadequate due to the leverage on the Porsche tensioner bearing. Of course, the tensioner could be engineered to have increased spring pressure, but then the timing belt on the 928 would then be too tight.
To make this tensioner work properly on the 928 engine, the tensioning bearing would need to be moved away from the crankshaft to reduce the leverage that the belt has on the roller....just like the Audi engineers did...and you did not.
And by the way....that belt that stretched was supplied, against my wishes, by Mark Anderson. You can bet that we never used anything but Factory Porsche belts on his engines ever again!
Look, I'm not going to further allow you to attack my credibiltiy, with cheap shots. Therefore, I refuse to discuss this matter any further with you in this forum.
And for those of you that don't understand the basic engineering problem here...simply try to remember that I have nothing to gain financially from this discussion. It has zero financial impact on me if you choose to use the factory pieces or Porken's thing. However, I will continue to use Porsche's method (regardless of how irresponsible that is), that has worked flawlessly for millions of miles.
Have fun guys...I'm out of this one.
01-04-2010, 05:48 AM
#77
Nordschleife Master
Interesting thread, no possible answer on "what is best", and the practical answer is simple;
If you have a mechanic replace the belt, do what they suggest.
If you do it yourself, and you know what you like, pick what suits you.
If you do it yourself, and your not really sure how to proceed, or that confident in your skills, maybe Porken's tensioner will be easier for you to get right.
If you have a mechanic replace the belt, do what they suggest.
If you do it yourself, and you know what you like, pick what suits you.
If you do it yourself, and your not really sure how to proceed, or that confident in your skills, maybe Porken's tensioner will be easier for you to get right.
01-04-2010, 04:11 PM
#78
Three Wheelin'
The only thing I would be worried about is the shoulder bolt that the pre S4 tensioners have. Porsche does not make the bolt anymore, and the only one available is the one with threads cut on it rather than being rolled on. Take your tensioner out and see if yours have this shoulder bolt, it might be like S4 since its a 86.5. If not see if you can get the S4 one for free from someone that has changed to the new tensioner.
About the belts I have no opinion, If you do decide to go with the Porsche one, buy it from someone that sells a lot of them, you don't want a belt that has been sitting on the dealerships shelf for 5 years, I think 928 international sells them a lot.
Honestly I would like to keep the warning light that comes with the stock tensioner. Do you guys remember that thread that Bill Ball started about the water pump failure that the dash belt light was showing a problem well before the pump seized ?
And you know what happens when the pump seizes it will damage the belt and the damaged belt could slip or snap and cause head damage. If you have the new tensioners and something goes wrong with the pump there will be no dash light to save your engine. And pump failure does happen, just go and put water pump failure on the search function and see how many threads you find, about 4 or 5 failures just happened a few months ago. For starters a proper head reconditioning will cost more than a 1000 dollar for a pair of 32 valve heads and that does not include new valves cost to replace bent ones. Also, if your machine shop turns out to be Sh*t, well you might have to go spend another amount to some other machine shop to redo the job like what I'm doing right now, and that's if your heads have not been turned to junk by the first machine shop.
And no, Im not trying to cause a "scare mongering" among the owners.
01-04-2010, 04:33 PM
#79
Inventor
Rennlist Member
Rennlist Member
In my humble opinion....you are being an arrogant (defined by Webster's as: exaggerating or disposed to exaggerate one's own worth or importance in an overbearing manner) ***.
It's not good enough for you to let me do things my way and you to do things your way and just walk away...you need to keep attacking. (I think everyone will consider your last sentence an arrogant attack.)
It's not good enough for you to let me do things my way and you to do things your way and just walk away...you need to keep attacking. (I think everyone will consider your last sentence an arrogant attack.)
1.) The Audi T/D does not have a 'positive stop'. False.
2.) The timing belt (especially one with the letters P-O-R-S-C-H-E printed on it) has no elasticity. False.
3.) A mysterious 'backforce' exists, waiting to inhale an unsuspecting engine. False.
Originally Posted by Marsellus Wallace
Night of the fight, you might feel a slight sting. That's pride fu**ing with you. Fu** pride! Pride only hurts . . . it never helps. You fight through that sh** 'cause a year from now, when you kickin' it in the Caribbean, you gonna say to yourself, "Marsellus Wallace was right."
Clearly, the motion from your tensioner when the engine is cold, is the "backforce" pushing on your tensioner and this makes the belt loose. You, me, and everyone else here knows that the belt doesn't stretch enough to make your tensioner "move"....nice try. It certainly isn't getting tighter...everyone also knows that. That leaves only one thing....the belt is getting looser from the "backforce"....just like I said from the very beginning. Certainly, everyone here clearly sees that...no matter how hard you attack me, trying to divert attention away from the obvious.
Originally Posted by Yoda
That place... is strong with the dark side of the Force. A domain of evil it is.
If you believe that the belt cannot stretch, then why don't you check/set the belt tension at TDC #6 or at any random point where the engine stops? (Maybe you do/did?) According to Greg's law, there should be no difference in tension at any point in a revolution.
The 928 belt is too narrow for 32 valve engines. It has too much much elasticity for what it is tasked to do. If the Engineers would spec a belt today (instead of chains like the Cayenne has), it would be at least 1-1/4" wide or wider (like the Audi belt in the picture posted previously).
If you took the time to think about my points, instead of trying to see how clever you can be making cute comebacks, you'd know that the Audi tensioner's ability to keep the belt tight is overcome by the leverage of the Porsche designed belt system. I'm sure that the Audi tensioner works great in its proper application. However, taking a piece from another vehicle and making an adaptor to make it fit on another rarely works. In this case, clearly the Audi tensioner's spring pressure is inadequate due to the leverage on the Porsche tensioner bearing. Of course, the tensioner could be engineered to have increased spring pressure, but then the timing belt on the 928 would then be too tight.
To make this tensioner work properly on the 928 engine, the tensioning bearing would need to be moved away from the crankshaft to reduce the leverage that the belt has on the roller....just like the Audi engineers did...and you did not.
To make this tensioner work properly on the 928 engine, the tensioning bearing would need to be moved away from the crankshaft to reduce the leverage that the belt has on the roller....just like the Audi engineers did...and you did not.
By your logic the stock 928 tensioner pulley should be moved farther away from the crank gear. Plastic tensioner arm bushes, and the early shoulder bolt are certainly less robust than the Audi parts, the tensioner arm is long, offset from center, and will experience even more of a bending force.
In the real world, however, a 928 engine spins -clockwise- (viewed from the front, check it out!), and the tensioner is on the 'loose' side of the belt. It's task is to keep the tension constant between the 1-4 cam gear, and the crank gear, so as to keep the belt tight on the crank gear. The tensioner pulley itself is not under tension.
(BTW: because the belt comes out flat from the crank gear to the oil pump gear, the tensioner pulley must be where it is, in order to have enough belt wrap around the gear.)
Your answer to any belt problem is more tension. The belt doesn't need more tension, it needs consistent tension, and better control.
And for those of you that don't understand the basic engineering problem here...simply try to remember that I have nothing to gain financially from this discussion. It has zero financial impact on me if you choose to use the factory pieces or Porken's thing. However, I will continue to use Porsche's method (regardless of how irresponsible that is), that has worked flawlessly for millions of miles.
01-04-2010, 04:52 PM
#80
Inventor
Rennlist Member
Rennlist Member
Interesting thread, no possible answer on "what is best", and the practical answer is simple;
If you have a mechanic replace the belt, do what they suggest.
If you do it yourself, and you know what you like, pick what suits you.
If you do it yourself, and your not really sure how to proceed, or that confident in your skills, maybe Porken's tensioner will be easier for you to get right.
If you have a mechanic replace the belt, do what they suggest.
If you do it yourself, and you know what you like, pick what suits you.
If you do it yourself, and your not really sure how to proceed, or that confident in your skills, maybe Porken's tensioner will be easier for you to get right.
Originally Posted by Mr. T
SHUT UP FOOL!
01-04-2010, 05:59 PM
#81
Captain Obvious
Super User
Super User
Yes. It can move out farther immediately, but takes a while to retract to a new setpoint. Longer when cold. Only when the engine is cold do you see such large variations, though. When warm you can feel the corrections, but hardly see the lever moving.
When retracting the piston on a cold tensioner in a vise, it goes: compress ~2mm, stopped, wait..., compress, stopped, wait..., etc. It takes >5 mins before you can insert the grenade pin.
When retracting the piston on a cold tensioner in a vise, it goes: compress ~2mm, stopped, wait..., compress, stopped, wait..., etc. It takes >5 mins before you can insert the grenade pin.
01-04-2010, 06:25 PM
#82
Inventor
Rennlist Member
Rennlist Member
When the engine is revved, the belt tightens all the way around the gears as they fight to accelerate, creating slack on the loose, tensioner side of the crank gear. The tensioner piston extends to take up the extra belt. As the cams reach the same speed as the crank, belt tension equalizes and the belt shrinks. The tensioner piston retracts to it's temporary limit. If the acceleration was severe enough, the piston may have extended farther than 2mm so the belt tension will be higher until the tensioner piston can retract to a new baseline.
As the engine expands from cold to hot, the piston retracts >2mm to compensate. Overnight, as the engine cools, and the distance from the 1-4 gear and the crank gear gets smaller, the piston extends to take up slack. When the engine is started in the morning, as the crankshaft is turned by the starter, loose belt between the crank gear, 5-8 gear, water pump, and 1-4 gear is taken up and passed to the tensioner pulley, so the piston extends further.
All cylinders fire with more or less power than others, but this is especially noticeable when the engine is cold. The uneven pulses accelerate or decelerate the crank creating more or less belt on the loose side. This is when the PKsn'r is worked the hardest absorbing these spikes.
The stock tensioner doesn't absorb large spikes, so the belt flaps. If there wasn't the 3 minute delay at startup, you would likely get many more [BELT TEN.] warnings on cold days!
01-04-2010, 06:25 PM
#83
Rennlist Member
This statement I believe to be very true and fully agree.
I understand m/cycle engine engineering much better from my racing days and DOHC engines are now always driven by chain with an oil supplied auto tensioner. These engines rev to +16k rpm and power to weight is out of sight.
01-04-2010, 07:02 PM
#84
Nordschleife Master
When a 1000 of the Porkentensioners have been installed, and 100 or so of them have been driven 50k miles or more, we will start to know how well they really work and what happens when they break. If you believe otherwise, listen to your buddy Mr T.
The factory system, with parts in good or new condition, and installed correctly is known to work.
The factory system, with parts in good or new condition, and installed correctly is known to work.
01-04-2010, 07:26 PM
#85
Rennlist Member
When a 1000 of the Porkentensioners have been installed, and 100 or so of them have been driven 50k miles or more, we will start to know how well they really work and what happens when they break. If you believe otherwise, listen to your buddy Mr T.
The factory system, with parts in good or new condition, and installed correctly is known to work.
The factory system, with parts in good or new condition, and installed correctly is known to work.
I'll glady report every year and hope other do also while the OEM folks 'maintain' their '70s technology.
01-04-2010, 07:30 PM
#86
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I'll glady report every year and hope other do also while the OEM folks 'maintain' their '70s technology.
I'm afraid that this is what people will come to believe, that somehow the PK system is maintenance (and therefore inspection) free. There may not be any scheduled maintenance on the tensioner itself but there's no reason to think (at least that I can see) that the inspection intervals should change at all, yet the temptation to lengthen them will be VERY strong.
01-04-2010, 07:30 PM
#87
Inventor
Rennlist Member
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When a 1000 of the Porkentensioners have been installed, and 100 or so of them have been driven 50k miles or more, we will start to know how well they really work and what happens when they break. If you believe otherwise, listen to your buddy Mr T.
The factory system, with parts in good or new condition, and installed correctly is known to work.
The factory system, with parts in good or new condition, and installed correctly is known to work.
My prediction?
Yes, your prediction.
Pain!
01-04-2010, 07:54 PM
#88
Nordschleife Master
I predict that if you predict that nothing unpredictable is going to happen, that you will be wrong.
Until a dozen or two of these devices fail its pointless to speculate.
Until a dozen or two of these devices fail its pointless to speculate.
01-04-2010, 08:02 PM
#89
Rest in Peace
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When they are extended if I can move them by hand, they are bad.
Is there something special about this one that is different than the rest of them?
01-04-2010, 08:09 PM
#90
Inventor
Rennlist Member
Rennlist Member
If the T/D is unmounted, at full extension, it cannot be pushed in by hand.
If it is installed, in stasis at it's operating tension, if you pull on the belt, or rotate the pulley with an allen key, you can retract the piston ~2mm for as long as you apply pressure. It takes some force to do this. A greater, constant force is required to retract the piston farther.
If it is installed, in stasis at it's operating tension, if you pull on the belt, or rotate the pulley with an allen key, you can retract the piston ~2mm for as long as you apply pressure. It takes some force to do this. A greater, constant force is required to retract the piston farther.