Cam timing inconsistant with each revolution
07-26-2010 | 03:43 PM
#136
Rennlist Member
Joined: Nov 2008
Posts: 1,745
Likes: 147
From: Grapevine, TX
Probably doesn't make much difference as numbers are estimates anyway but that engine is very early prototype which used carburetor and didn't yet have washer tensioner setup. Notice how there appears to be plate where tensioner roller is mounted and bolts to secure it to block and adjust tension.
when I installed my tensioner I used a short bolt with a little sealant on the threads and it seems to have worked well. I wasn't comfortable with the set screw plug either.
07-26-2010 | 03:56 PM
#137
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,177
Likes: 412
Ken,
Let me explain more fully what I tried to say before: You're asking us to accept the tensioner design on faith. We're asked to do that with respect to religion. But this is not religion, it is engineering, and accepting a new design on "faith" is not appropriate. I know little about religion, but I am quite comfortable discussing engineering, having spent my life doing it (I am not a young guy).
Sound engineering designs are based on analysis and testing. And there are some legitimate questions here: the Audi tensioner is well-proven, but it is being used in a different application: A different geometry which may or may not be significant, with a larger belt driving higher loads which may or may not be significant. That makes it a "new design", different from the factory tensioner and different than the original Audi application.
There are generally two ways to prove out a new design: careful analysis, and thorough testing. Generally both are done. I assume the spec's for the Audi tensioner are not available, and we cannot duplicate the original environment (which I believe is an Audi 2.7L 4-cam V6). So the best we can do with a design analysis is to compare loads, resonant frequencies etc with the original application: If those match then we can "inherit" the confidence in the original design.
That is not simple (measuring dynamic tension of a moving belt is not trivial) and I assume you haven't done it. Which is fine, because a design can also be proved out with testing. Which is what we are all doing now.
I have reasonable confidence in the design, and we have your tensioners in both of our cars. But I do consider it experimental, and I keep a careful eye on them. I am happy to do that because we work on our own cars, and if things start to look unhappy then I am out a bit of labor. And if things come apart and wreck the valves, well it was my choice. Personally I think there is very little chance of that, but I am not 100% certain that the Audi tensioner won't suffer premature failure because of the change in its application.
Guys with professional shops have a different basis for their choices. If a part fails, they own that failure and need to make it right. That's quite different than you and I.
So in GB's position I would be asking for exactly what he has asked for: the data to support a design analysis. It's not available, and probably can't be available with the means available to this community. And there are differences: The Audi tensioner was designed for a smaller motor, the belt tension is lower than Porsche intended, and the damping is handled differently (and almost certainly better). Those things may be just fine but the only way that we know for sure is by thorough testing. When hundreds of tensioners have gone six years and 60,000 miles then the confidence level will be very high. But we're not there yet.
My suggestion is that it is not reasonable to expect professional shops to be part of the testing program, and it is not reasonable to criticize them for declining to do so-- or for asking for the data that they need to get comfortable with a design in lieu of extensive testing.
Cheers, Jim
Let me explain more fully what I tried to say before: You're asking us to accept the tensioner design on faith. We're asked to do that with respect to religion. But this is not religion, it is engineering, and accepting a new design on "faith" is not appropriate. I know little about religion, but I am quite comfortable discussing engineering, having spent my life doing it (I am not a young guy).
Sound engineering designs are based on analysis and testing. And there are some legitimate questions here: the Audi tensioner is well-proven, but it is being used in a different application: A different geometry which may or may not be significant, with a larger belt driving higher loads which may or may not be significant. That makes it a "new design", different from the factory tensioner and different than the original Audi application.
There are generally two ways to prove out a new design: careful analysis, and thorough testing. Generally both are done. I assume the spec's for the Audi tensioner are not available, and we cannot duplicate the original environment (which I believe is an Audi 2.7L 4-cam V6). So the best we can do with a design analysis is to compare loads, resonant frequencies etc with the original application: If those match then we can "inherit" the confidence in the original design.
That is not simple (measuring dynamic tension of a moving belt is not trivial) and I assume you haven't done it. Which is fine, because a design can also be proved out with testing. Which is what we are all doing now.
I have reasonable confidence in the design, and we have your tensioners in both of our cars. But I do consider it experimental, and I keep a careful eye on them. I am happy to do that because we work on our own cars, and if things start to look unhappy then I am out a bit of labor. And if things come apart and wreck the valves, well it was my choice. Personally I think there is very little chance of that, but I am not 100% certain that the Audi tensioner won't suffer premature failure because of the change in its application.
Guys with professional shops have a different basis for their choices. If a part fails, they own that failure and need to make it right. That's quite different than you and I.
So in GB's position I would be asking for exactly what he has asked for: the data to support a design analysis. It's not available, and probably can't be available with the means available to this community. And there are differences: The Audi tensioner was designed for a smaller motor, the belt tension is lower than Porsche intended, and the damping is handled differently (and almost certainly better). Those things may be just fine but the only way that we know for sure is by thorough testing. When hundreds of tensioners have gone six years and 60,000 miles then the confidence level will be very high. But we're not there yet.
My suggestion is that it is not reasonable to expect professional shops to be part of the testing program, and it is not reasonable to criticize them for declining to do so-- or for asking for the data that they need to get comfortable with a design in lieu of extensive testing.
Cheers, Jim
My question was rhetorical (and snippy
), but thank you for the larger context.It is about faith. When you pull the pin and turn over the engine for the first time, you are probably holding your breath. I still do. But I did this with the stock tensioner system too. From that point on, though, in contrast to the stock system, there is a sense of peace, knowing the belt is controlled automatically.
The PKsn'r was an organic development, seeded by a desire to counter the accepted failings of the stock tensioner system. I did not have the facilities (or faculties) to create a tensioner from scratch, so I looked for a proven system that would fit. I looked at many, many tensioners, and feel fortunate in finding the Audi 2.8 30 valve tensioner, in that it was proven, with no issues that I could discover since it's inception, and fit. It has the same size tensioner pulley as stock, and it even fit through the old hole in center cover! I tested it on my engines, and was pleased to find that the tension was acceptable, too.
I see the Audi system as being under-stressed used on a 928 engine. The 2.8 spins faster, and more quickly than the portly V8. The belt on the 2.8 is heavier, wider and thicker. (The only belt length that the tensioner sees is the distance from the cam gear to the crank gear, total length is not a factor.) The tensioner and guide pulleys are set higher in order to save space. The original 2.8 belt change interval was >100K miles, and the components reflect this. The pulley bearing is massive. The bushings are steel. The system is very compact. Anyone who's compared the Audi to the stock parts can't help but chuckle at how cute the stock parts are.
It is obvious to any observer of a running engine with the covers off that the PKsn'r is a superior belt management system, and this talk of belt tension is a bit like trying to put the proverbial cherry back in the box, and a distraction. There is no specification from Audi for the tension. The static tension between the 1-4 gear, and the crank gear is irrelavent as soon as the engine begins turning. GB has admitted in a previous 'discussion' that he trashed one of Mark Anderson's race engines at startup when the belt skipped teeth. If the stock system will allow enough slack belt to form to skip teeth, even when the esteemed GB has set the static tension, how much faith should regular folks put in a tension warning light that has a 3-minute delay when the engine is started? If it can happen in sunny SoCal, what about when the engine is started in northern Canada?
GB introduced this notion that the tension is less with a PKsn'r by spinning the engine by hand, and pushing on the tensioner piston. No measurement after running the engine to allow the hydraulic action to work. (A simple Kempf tool check that anyone can do will show the tension is fine.) Now, he's pushing this cam timing notion, which came about, again, from improper procedure on the part of the original poster. From the start, for whatever reason, GB has disliked the PKsn'r, and has jumped on any opportunity to cast aspersion to it. (BTW: I would like to believe that MA did not conspire to help GB in his quixotian quest {post #41}, and that he was genuinely interested in selling them when he emailed me about doing so.)
The PKsn'r was not made or 'marketed' for repair shops. It was made for the home mechanic who doesn't want to worry about retensioning the belt, or spinning the engine to redline. (15K miles? It's a Porsche, not a Ferrari!)
Gruß,
Ken
Last edited by PorKen; 07-26-2010 at 04:43 PM. Reason: forgot pic
07-26-2010 | 03:57 PM
#138
Former Vendor
Joined: Feb 2005
Posts: 15,230
Likes: 2,489
From: Anaheim
Ken,
Let me explain more fully what I tried to say before: You're asking us to accept the tensioner design on faith. We're asked to do that with respect to religion. But this is not religion, it is engineering, and accepting a new design on "faith" is not appropriate. I know little about religion, but I am quite comfortable discussing engineering, having spent my life doing it (I am not a young guy).
Sound engineering designs are based on analysis and testing. And there are some legitimate questions here: the Audi tensioner is well-proven, but it is being used in a different application: A different geometry which may or may not be significant, with a larger belt driving higher loads which may or may not be significant. That makes it a "new design", different from the factory tensioner and different than the original Audi application.
There are generally two ways to prove out a new design: careful analysis, and thorough testing. Generally both are done. I assume the spec's for the Audi tensioner are not available, and we cannot duplicate the original environment (which I believe is an Audi 2.7L 4-cam V6). So the best we can do with a design analysis is to compare loads, resonant frequencies etc with the original application: If those match then we can "inherit" the confidence in the original design.
That is not simple (measuring dynamic tension of a moving belt is not trivial) and I assume you haven't done it. Which is fine, because a design can also be proved out with testing. Which is what we are all doing now.
I have reasonable confidence in the design, and we have your tensioners in both of our cars. But I do consider it experimental, and I keep a careful eye on them. I am happy to do that because we work on our own cars, and if things start to look unhappy then I am out a bit of labor. And if things come apart and wreck the valves, well it was my choice. Personally I think there is very little chance of that, but I am not 100% certain that the Audi tensioner won't suffer premature failure because of the change in its application.
Guys with professional shops have a different basis for their choices. If a part fails, they own that failure and need to make it right. That's quite different than you and I.
So in GB's position I would be asking for exactly what he has asked for: the data to support a design analysis. It's not available, and probably can't be available with the means available to this community. And there are differences: The Audi tensioner was designed for a smaller motor, the belt tension is lower than Porsche intended, and the damping is handled differently (and almost certainly better). Those things may be just fine but the only way that we know for sure is by thorough testing. When hundreds of tensioners have gone six years and 60,000 miles then the confidence level will be very high. But we're not there yet.
My suggestion is that it is not reasonable to expect professional shops to be part of the testing program, and it is not reasonable to criticize them for declining to do so-- or for asking for the data that they need to get comfortable with a design in lieu of extensive testing.
Cheers, Jim
Let me explain more fully what I tried to say before: You're asking us to accept the tensioner design on faith. We're asked to do that with respect to religion. But this is not religion, it is engineering, and accepting a new design on "faith" is not appropriate. I know little about religion, but I am quite comfortable discussing engineering, having spent my life doing it (I am not a young guy).
Sound engineering designs are based on analysis and testing. And there are some legitimate questions here: the Audi tensioner is well-proven, but it is being used in a different application: A different geometry which may or may not be significant, with a larger belt driving higher loads which may or may not be significant. That makes it a "new design", different from the factory tensioner and different than the original Audi application.
There are generally two ways to prove out a new design: careful analysis, and thorough testing. Generally both are done. I assume the spec's for the Audi tensioner are not available, and we cannot duplicate the original environment (which I believe is an Audi 2.7L 4-cam V6). So the best we can do with a design analysis is to compare loads, resonant frequencies etc with the original application: If those match then we can "inherit" the confidence in the original design.
That is not simple (measuring dynamic tension of a moving belt is not trivial) and I assume you haven't done it. Which is fine, because a design can also be proved out with testing. Which is what we are all doing now.
I have reasonable confidence in the design, and we have your tensioners in both of our cars. But I do consider it experimental, and I keep a careful eye on them. I am happy to do that because we work on our own cars, and if things start to look unhappy then I am out a bit of labor. And if things come apart and wreck the valves, well it was my choice. Personally I think there is very little chance of that, but I am not 100% certain that the Audi tensioner won't suffer premature failure because of the change in its application.
Guys with professional shops have a different basis for their choices. If a part fails, they own that failure and need to make it right. That's quite different than you and I.
So in GB's position I would be asking for exactly what he has asked for: the data to support a design analysis. It's not available, and probably can't be available with the means available to this community. And there are differences: The Audi tensioner was designed for a smaller motor, the belt tension is lower than Porsche intended, and the damping is handled differently (and almost certainly better). Those things may be just fine but the only way that we know for sure is by thorough testing. When hundreds of tensioners have gone six years and 60,000 miles then the confidence level will be very high. But we're not there yet.
My suggestion is that it is not reasonable to expect professional shops to be part of the testing program, and it is not reasonable to criticize them for declining to do so-- or for asking for the data that they need to get comfortable with a design in lieu of extensive testing.
Cheers, Jim
I've been trying to get this point across for almost three years and all I've ever gotten back is wise *** condenscending defensive bull****, making fun of me and my shop.
Hopefully you do better....although I'm not sure I even care anymore.
07-26-2010 | 04:20 PM
#139
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,177
Likes: 412
07-26-2010 | 05:24 PM
#140
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,177
Likes: 412
07-26-2010 | 05:35 PM
#141
Former Vendor
Joined: Feb 2005
Posts: 15,230
Likes: 2,489
From: Anaheim
I see the Audi system as being under-stressed used on a 928 engine. The 2.8 spins faster, and more quickly than the portly V8. The belt on the 2.8 is heavier, wider and thicker. (The only belt length that the tensioner sees is the distance from the cam gear to the crank gear, total length is not a factor.) The tensioner and guide pulleys are set higher in order to save space. The original 2.8 belt change interval was >100K miles, and the components reflect this. The pulley bearing is massive. The bushings are steel. The system is very compact. Anyone who's compared the Audi to the stock parts can't help but chuckle at how cute the stock parts are.
GB has admitted in a previous 'discussion' that he trashed one of Mark Anderson's race engines at startup when the belt skipped teeth. If the stock system will allow enough slack belt to form to skip teeth, even when the esteemed GB has set the static tension, how much faith should regular folks put in a tension warning light that has a 3-minute delay when the engine is started?
If the piston moves in and out, when you turn the engine by hand...the cam timing is moving, too! Even you can "see" this! How do you control this???? That is the entire question in this tread! He can't set the cam timing with the engine running, or when it is turned over with the starter!!!!
Only made for the home guy, that wants to "hold his breath" every time he turns the key. Like you do!
That pretty much says it all.....
07-26-2010 | 05:44 PM
#144
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,177
Likes: 412
07-26-2010 | 06:25 PM
#145
Former Vendor
Joined: Feb 2005
Posts: 15,230
Likes: 2,489
From: Anaheim
Quotes from Porken:
"Hold your breath when you start it. I do, everytime."
"Only made for the home guy, not for shops." ???????????
"Caution: Not made to take to redline."
Now there's the part everyone needs!
"Hold your breath when you start it. I do, everytime."
"Only made for the home guy, not for shops." ???????????
"Caution: Not made to take to redline."
Now there's the part everyone needs!
07-26-2010 | 08:07 PM
#147
Addict
Rennlist Member
Rennlist Member
Joined: Jul 2001
Posts: 7,330
Likes: 110
From: Shawnee, KS, USA
The plug has no head and seemed a bit loose to me as well. It threaded in with no resistance and nothing to stop it. That bothered me from the get-go. I think a bolt could work, although the stock shaft appears to be machined flat underneath and we know it seals, so we went with that after the first ones leaked.
Another related thing to point out here: if you don't leave on (or reinstall) that three hole bracket on the WP (the one that supported the outside part of the shaft (pivot bolt/pin/whatever it's called) that supports the idler roller / tension roller assembly, then you'll regret it when you attempt to reinstall your center timing belt cover. The center bolt goes through the timing belt cover, and if that bracket is missing, you'll discover that there's no backing when you attempt to torque down that bolt. It'll distort the cover by a little more than three mm (the thickness of the now-missing bracket) if you decide to torque it down anyway. Luckily, I noticed something bad was happening and went back and reinstalled the bracket (minus the left end that originally attached to the end of the roller assembly; I just left the "roller assembly pin end" hanging in space). I contemplated just putting a thick washer back there, but that seems unwise, as I can see forgetting about it and then during some future maintenance, pulling the cover off and having that washer dropping unnoticed into the crank gear or something; just too risky.
Now I regret not having just gone back and removing the set screw, reinstalling the shaft and bracket, and everything would have been cool.
As long as that set screw doesn't leak, I guess there's no harm done.
Anyway, IMHO, I'd recommend that the PKsn'r instructions be updated to recommend leaving that bracket and shaft intact; it's likely to cause more trouble by leaving it off than leaving it alone.
And... Ken, IMHO, a lot of your posts in this thread don't exactly inspire a lot of confidence in those of us (like me) who aren't real mechanics by any stretch, but just DIYers. It appears to me that you've got a good product with the PKsn'r, but I'd really like to see as much professionalism as possible displayed by the guy who's behind a what's now a super-critical part of my car. Remember that there are (and will be, for years to come) a lot more guys like me reading this thread, trying to decide whether or not to take the PKsn'r plunge. Seems like it would be a great idea to cover all the bases, regardless of where the debating points come from. I hope that doesn't make me a target, too; I'm just trying to make something constructive out of what has become an unnecessarily nasty thread.
Last edited by Ed Scherer; 07-26-2010 at 08:29 PM.
07-26-2010 | 09:08 PM
#149
Inventor
Rennlist Member
Rennlist Member
Joined: Sep 2002
Posts: 10,177
Likes: 412
Anyway, IMHO, I'd recommend that the PKsn'r instructions be updated to recommend leaving that bracket and shaft intact; it's likely to cause more trouble by leaving it off than leaving it alone.
And... Ken, IMHO, a lot of your posts in this thread don't exactly inspire a lot of confidence in those of us (like me) who aren't real mechanics by any stretch, but just DIYers. It appears to me that you've got a good product with the PKsn'r, but I'd really like to see as much professionalism as possible displayed by the guy who's behind a what's now a super-critical part of my car. Remember that there are a lot more guys like me reading this thread, trying to decide whether or not to take the PKsn'r plunge. Seems like it would be a great idea to cover all the bases, regardless of where the debating points come from. I hope that doesn't make me a target, too; I'm just trying to make something constructive out of what has become an unnecessarily nasty thread.
And... Ken, IMHO, a lot of your posts in this thread don't exactly inspire a lot of confidence in those of us (like me) who aren't real mechanics by any stretch, but just DIYers. It appears to me that you've got a good product with the PKsn'r, but I'd really like to see as much professionalism as possible displayed by the guy who's behind a what's now a super-critical part of my car. Remember that there are a lot more guys like me reading this thread, trying to decide whether or not to take the PKsn'r plunge. Seems like it would be a great idea to cover all the bases, regardless of where the debating points come from. I hope that doesn't make me a target, too; I'm just trying to make something constructive out of what has become an unnecessarily nasty thread.
Wherever possible, I have explained the PKsn'r concept as best as I can, but this is a discussion group, not a user manual. I do not have control over the participants, or the quality of information provided by others.
Many posts ago I realized that GB did not care what I said, he would just find a new avenue of attack. Since he continues to post misinformation that I must counter, I may as well have some fun at his expense. Frankly, the faster it drifts into the abyss, the better, IMO.
That said, there have been a few constructive posts in this thread. For myself, I am pleased to have made the conceptual leap from a limited view of belt tension to a more holistic idea of belt management.
I guess I did hit below the belt (tension?), sorry for that.
07-26-2010 | 09:09 PM
#150
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Feb 2009
Posts: 18,061
Likes: 8
Perhaps the one thing that has been PROVEN is that the 928 engine will run with a wide variance in tension may not run 100% but will run. With a none functioning tension warning light it might even seem that everything is O K .