One man's tensioner solution
03-16-2007, 06:41 PM
#106
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Mark, have you ever tried to compress a modern hydraulic tensioner?
You have to use a vice and go real slow, 200 pounds is not going to do it, so it does not surprise me at all that 200 did nothing on a stock 928 tensioner.
The beauty of a set up like this is that it will compensate for belt stretch and temp variations, with the warning system intact, you could set it up once at 5.0 and forget about it until it was due a belt change.
Nobody to my knowledge has been talking about the little spring on the end for the warning system being part of what gives it its tension, why are you?
You have to use a vice and go real slow, 200 pounds is not going to do it, so it does not surprise me at all that 200 did nothing on a stock 928 tensioner.
The beauty of a set up like this is that it will compensate for belt stretch and temp variations, with the warning system intact, you could set it up once at 5.0 and forget about it until it was due a belt change.
Nobody to my knowledge has been talking about the little spring on the end for the warning system being part of what gives it its tension, why are you?
03-16-2007, 06:44 PM
#107
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Hammer, I applaud your creativity here, but i merely did not look at a picture and say, "the sky is fallling" . I noticed a fundamental differnce that could have been overlooked. a solid engagement of the tensioner piston vs a spring. This gives me concern for you, becasue of two reasons. 1. springs compress. if the force on the spring is just enough to move it a millimeter, you could have yourself a bucket of bent valves. 2. you also have the chance of over tensioning the belt if comprssed too much and wearing out the water pump and pulleys, or worse, damaging the belt.
there are so many factors in what you are doing, i was just casting a warning in case you didnt consider them. do you understand the natural frequency of the spring part and how resonance can amplify any forces acting on the spring? that in itself, would worry me most. these engines are amazing that they stay together at 6500rpm. so many forces all being taken into account when porsche designed it. this critical element, and the fact that we have the longest belt of most any production car, worries me that any attemps to improving the system could cause serious issues.
Mk
there are so many factors in what you are doing, i was just casting a warning in case you didnt consider them. do you understand the natural frequency of the spring part and how resonance can amplify any forces acting on the spring? that in itself, would worry me most. these engines are amazing that they stay together at 6500rpm. so many forces all being taken into account when porsche designed it. this critical element, and the fact that we have the longest belt of most any production car, worries me that any attemps to improving the system could cause serious issues.
Mk
Originally Posted by 6.0-928S
To All,
This is what happened that leads me to believe that this tensioner is within the ranges necessary. I mocked up the engine & belt on the stand with the tensioner setup torqued in place. I rigged up a test light to the circuit. I cranked up the adjusting bolt until the light came on. I tightened the adjuster up slightly until the belt tension was within the proper range on my $59 tension gauge. I spun the motor over several times checking at intervals to see if the tension changed. The tension was stabilized. At that point I saw about .060" compression in the tensioner. With a pry bar I pushed the tensioner roller swingarm into the tensioner mimmicking the belt/engine expansion when warm or at higher rpm. The tensioner compressed about .031" & immediately sprung back when I let go. It was NOT easy to compress. I'm just over 6 foot & 235 pounds & I can't compress this thing without a vice although it was easier with the prybar. But by no means sloppy. That leads me to believe that this tensioner will stay within factory limits enough for me to test on a running engine. I'm thinking of putting a pressure tester on the belt somewhere when running like they use on the Formula 1 cars. (I know someone who has one of those systems that they removed from their car a few years ago & tried to sell me but I didn't want it at that time. I know he still has it) But that will be as a last resort. I have no reason to believe that the tensioner won't work as I planned at this time. So when someone merely looks at a picture & says 'the sky is falling' maybe they should do a similar amount of testing on their mouth before criticizing the work of others.
There, ...I feel much better now!
Regards, Hammer
This is what happened that leads me to believe that this tensioner is within the ranges necessary. I mocked up the engine & belt on the stand with the tensioner setup torqued in place. I rigged up a test light to the circuit. I cranked up the adjusting bolt until the light came on. I tightened the adjuster up slightly until the belt tension was within the proper range on my $59 tension gauge. I spun the motor over several times checking at intervals to see if the tension changed. The tension was stabilized. At that point I saw about .060" compression in the tensioner. With a pry bar I pushed the tensioner roller swingarm into the tensioner mimmicking the belt/engine expansion when warm or at higher rpm. The tensioner compressed about .031" & immediately sprung back when I let go. It was NOT easy to compress. I'm just over 6 foot & 235 pounds & I can't compress this thing without a vice although it was easier with the prybar. But by no means sloppy. That leads me to believe that this tensioner will stay within factory limits enough for me to test on a running engine. I'm thinking of putting a pressure tester on the belt somewhere when running like they use on the Formula 1 cars. (I know someone who has one of those systems that they removed from their car a few years ago & tried to sell me but I didn't want it at that time. I know he still has it) But that will be as a last resort. I have no reason to believe that the tensioner won't work as I planned at this time. So when someone merely looks at a picture & says 'the sky is falling' maybe they should do a similar amount of testing on their mouth before criticizing the work of others.
There, ...I feel much better now!
Regards, Hammer
03-16-2007, 06:49 PM
#108
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I dont have oil in this one, so there is no hydralics in this one either. (stock 928) and to your point, if it doesnt move with 200lbs of force, great. but, if the spring does, and it will, what could be the consequences?
i only brought up the little spring incase someone was considering that part of the compliance of the system. glad youre not.
The problem with the warning system now,is that it is always pushing on the belt. so, if the spring did get forced in, it could be enough to have the belt skip teeth and the contact may never be broken. i have to think about that one for a moment, but it seems that the spring may short circuit (no pun) that entire mechanism's purpose (the warning circuit)
MK
i only brought up the little spring incase someone was considering that part of the compliance of the system. glad youre not.
The problem with the warning system now,is that it is always pushing on the belt. so, if the spring did get forced in, it could be enough to have the belt skip teeth and the contact may never be broken. i have to think about that one for a moment, but it seems that the spring may short circuit (no pun) that entire mechanism's purpose (the warning circuit)
MK
Originally Posted by blown 87
Mark, have you ever tried to compress a modern hydraulic tensioner?
You have to use a vice and go real slow, 200 pounds is not going to do it, so it does not surprise me at all that 200 did nothing on a stock 928 tensioner.
The beauty of a set up like this is that it will compensate for belt stretch and temp variations, with the warning system intact, you could set it up once at 5.0 and forget about it until it was due a belt change.
Nobody to my knowledge has been talking about the little spring on the end for the warning system being part of what gives it its tension, why are you?
You have to use a vice and go real slow, 200 pounds is not going to do it, so it does not surprise me at all that 200 did nothing on a stock 928 tensioner.
The beauty of a set up like this is that it will compensate for belt stretch and temp variations, with the warning system intact, you could set it up once at 5.0 and forget about it until it was due a belt change.
Nobody to my knowledge has been talking about the little spring on the end for the warning system being part of what gives it its tension, why are you?
03-16-2007, 07:03 PM
#109
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Originally Posted by Mike Simard
But Mark, there's a seperate damper in the Volvo unit. It sounds like you see the picture on page 1 and believe the shaft inside the spring is dormant. Hammer said that it's a damper with it's own internal oil supply. Hammer is that correct?
Hammer
03-16-2007, 07:05 PM
#111
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The tensioner from a 928 is not a modern tensioner.
The spring is only going to move out, not in, unless you put it in a vice.
If they did there would be lots of cars not on the road today.
The warning system spring is there because there is no automatic compensation, once the tension on a stock 928 is set, it (the arm that puts the tension on the belt) is going to stay at that position regarless of what belt tension is.
All the little spring is there for is to try to push the arm away and break the circuit. It is not going to do much of anything for belt tension.
The spring is only going to move out, not in, unless you put it in a vice.
If they did there would be lots of cars not on the road today.
The warning system spring is there because there is no automatic compensation, once the tension on a stock 928 is set, it (the arm that puts the tension on the belt) is going to stay at that position regarless of what belt tension is.
All the little spring is there for is to try to push the arm away and break the circuit. It is not going to do much of anything for belt tension.
Originally Posted by mark kibort
I dont have oil in this one, so there is no hydralics in this one either. (stock 928) and to your point, if it doesnt move with 200lbs of force, great. but, if the spring does, and it will, what could be the consequences?
i only brought up the little spring incase someone was considering that part of the compliance of the system. glad youre not.
The problem with the warning system now,is that it is always pushing on the belt. so, if the spring did get forced in, it could be enough to have the belt skip teeth and the contact may never be broken. i have to think about that one for a moment, but it seems that the spring may short circuit (no pun) that entire mechanism's purpose (the warning circuit)
MK
i only brought up the little spring incase someone was considering that part of the compliance of the system. glad youre not.
The problem with the warning system now,is that it is always pushing on the belt. so, if the spring did get forced in, it could be enough to have the belt skip teeth and the contact may never be broken. i have to think about that one for a moment, but it seems that the spring may short circuit (no pun) that entire mechanism's purpose (the warning circuit)
MK
03-17-2007, 01:32 AM
#112
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Originally Posted by 6.0-928S
Where do you keep coming off with the undamped spring? Maybe you should read the previous posts before you put yer chops in gear. Read my lips........THERE IS AN OIL FILLED DAMPER TUBE IN THE CENTER OF THE SPRING ASSEMBLY!
Heh heh...sorry, couldn't resist.
And good luck with the mod and keep us posted.
Ed
03-17-2007, 02:23 AM
#113
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Hammer- you are to be commended for your creativity. You've taken a part from a Ford Taurus and made it work on a Porsche. Or you've manipulated a Volvo part to work on a Porsche model. Great. Happy now? I sure am. I applaud your efforts, but I think you are trying to fix a problem that doesn't exist. The Porsche tensioner not only keeps the belt correctly tight, it does it at the varying temperatures that an engine will operate at. Sorry, but I don't intend to copy your modifications. I think Porsche's originals are better.
I DO think you mods are WAY hott however.
N!
I DO think you mods are WAY hott however.
N!
03-17-2007, 03:03 AM
#114
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LOL..W in TF happened to THIS thread??? YEEEEEEEEhawwww
I say go for it Hammer! We're all watchin and lovin it. If you scrap your engine because of this, then we all learned a new thing here, if not...uhm...we all learned a new thing here.
We can all hypothesize for a long time to come over this, so just do it. No one really knows why in the hell Porsche designed this thing the way they did anyway! They DID have springs back in those days!
Fire it up and run it like ya stole it! Let us know how it goes...
I say go for it Hammer! We're all watchin and lovin it. If you scrap your engine because of this, then we all learned a new thing here, if not...uhm...we all learned a new thing here.
We can all hypothesize for a long time to come over this, so just do it. No one really knows why in the hell Porsche designed this thing the way they did anyway! They DID have springs back in those days!
Fire it up and run it like ya stole it! Let us know how it goes...
03-17-2007, 03:18 AM
#115
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What do they use to tension the belt on other higher reving modern performance cars, or even the F1 cars. They are V8's now. Are they belt or chain? What about the cayenne. It is a V8. How are Porsche addressing this with there up to date technology now.
03-17-2007, 09:24 AM
#116
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IIRR Cayenne use chain like many other modern engines.
928 system is basically old style fixed system where roller is set to some point and leaved there. In this case this point just moves while washers contract when they get warmer. Belt tension varies much more during one crank rotation than what bimetal washers can take care acting as springs. This is easy to test just by measuring belt tension while crank is in many different positions. When 9201 or Kempf gives 5.2 reading in TDC range it will be during 360 degress revolution could be 4.5-5.5 or something similar. 5.2 measurement in TDC results acceptable tension in entire crank rotation. My worry is, will other systems keep tension in this same range or even close to it during 360 rotation? Can they do that if they don't take block expansion into account same way as Porsche system does?
'83 MY change with external oil filler holes was done to take up slack in system when tension changes during rotation. It will allow roller to contract at certain speed which is determined by how much oil can escape around moving piston when other route around washers is blocked. This will function as one way damper and limit quick roller movement. Roller can still follow belt quickly as oil flows freely to other direction. Spring in Volvo system must provide similar quick movement into expansion direction while damper in it should provide slowing into compress direction. Will it do that? Possibly but is movement as free into one direction and as limited into other like in Porsche system?
Belt tension warning spring is very weak compared to what it takes to compress bimetal washers. Also tension changes a lot while bolt is just barely rotated as other have pointed out. There is also one old thread in archives where I list some measurements how much rotation changes tension. I don't see washers acting as spring based on how solid they are and how little movement adjustment takes from above tensioner warning point to correct tension.
Kibort has been extremely lucky when he hasn't seen any wear while running without oil. I have seen opposite happen. Shaft around which washers are stacked was heavily worn and teflon on housing almost totally gone because lack of lubrication. Shaft was so worn that it was easy to see how some of the washers had duck "holes" for themselves in it and while being in these holes they not just prevented their own movement but also any meaningful movement on any washer further away from roller. First to suffer from lack of movement are cam gears and next in line are belt roller and cam bearing surfaces.
Being inventive and using latest techology is very good thing. Before that can be done its important to understand which were parameters original system was designed to meet. Above is what I think is going on in Porsche system.
928 system is basically old style fixed system where roller is set to some point and leaved there. In this case this point just moves while washers contract when they get warmer. Belt tension varies much more during one crank rotation than what bimetal washers can take care acting as springs. This is easy to test just by measuring belt tension while crank is in many different positions. When 9201 or Kempf gives 5.2 reading in TDC range it will be during 360 degress revolution could be 4.5-5.5 or something similar. 5.2 measurement in TDC results acceptable tension in entire crank rotation. My worry is, will other systems keep tension in this same range or even close to it during 360 rotation? Can they do that if they don't take block expansion into account same way as Porsche system does?
'83 MY change with external oil filler holes was done to take up slack in system when tension changes during rotation. It will allow roller to contract at certain speed which is determined by how much oil can escape around moving piston when other route around washers is blocked. This will function as one way damper and limit quick roller movement. Roller can still follow belt quickly as oil flows freely to other direction. Spring in Volvo system must provide similar quick movement into expansion direction while damper in it should provide slowing into compress direction. Will it do that? Possibly but is movement as free into one direction and as limited into other like in Porsche system?
Belt tension warning spring is very weak compared to what it takes to compress bimetal washers. Also tension changes a lot while bolt is just barely rotated as other have pointed out. There is also one old thread in archives where I list some measurements how much rotation changes tension. I don't see washers acting as spring based on how solid they are and how little movement adjustment takes from above tensioner warning point to correct tension.
Kibort has been extremely lucky when he hasn't seen any wear while running without oil. I have seen opposite happen. Shaft around which washers are stacked was heavily worn and teflon on housing almost totally gone because lack of lubrication. Shaft was so worn that it was easy to see how some of the washers had duck "holes" for themselves in it and while being in these holes they not just prevented their own movement but also any meaningful movement on any washer further away from roller. First to suffer from lack of movement are cam gears and next in line are belt roller and cam bearing surfaces.
Being inventive and using latest techology is very good thing. Before that can be done its important to understand which were parameters original system was designed to meet. Above is what I think is going on in Porsche system.
03-17-2007, 06:00 PM
#117
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Here is the dissected tensioner. Hopefully you can see the valving ports in the piston. It was filled with a lightweight oil. After removing the large spring I could pump the central tube in & out and feel the oil being forced back & forth.
Hammer
Hammer
