Timing belt reinstall - Another PK tensioner over extended?
05-29-2016, 06:40 PM
#61
Captain Obvious
Super User
Super User
And yet, we have ONE documented failure due to PKT (Hai's problem is still undiagnosed IMO) and that was a broken bolt...I don't recall anyone saying that that one had elongated the holes due to over-extension, but I don't really know. So if the risk is as great as implied here, we'd see far more failures. HOWEVER...that's where my previous question becomes important. How rare is this scenario?
I would be very interesting to know how far the tensioner is extended after a few years of use? Are there many that are passed the extension limit?
05-29-2016, 09:18 PM
#62
Rennlist Member
Thread Starter
Did you measure it?
Did you have to modify it?
05-29-2016, 10:11 PM
#63
Rennlist Member
And yet, we have ONE documented failure due to PKT (Hai's problem is still undiagnosed IMO) and that was a broken bolt...I don't recall anyone saying that that one had elongated the holes due to over-extension, but I don't really know. So if the risk is as great as implied here, we'd see far more failures. HOWEVER...that's where my previous question becomes important. How rare is this scenario?
One was Jim M's GTS, the PKT dismounted itself from the block with a fractured M8 flathead, the two M8 flange-heads that unscrewed themselves (one completely, one partially), and the two plates that make up the bracket separated. There is no definitive evidence for which happened first.
The second was the tension pulley leaving the bracket on an Aussie race car, on the track. The M8 fastener fractured.
These two events led to the "black" version.
We put 70K on an early PKT on our GT: 50K then a belt change and a new roller/lever, then another 20K before swapping back to stock in late 2013. The initial extension was over 7mm (around 7.5 mm) for new belts, so I queried Ken and he said "fuggetaboutit" so we did. It didn't change appreciably further but I also did not make careful measurements after that-- it was billed as a install-and-forget-about-it device.
The concern is the initial measurement. Why would an engine with new/good gears and pulleys, and absent machined heads, be any different than whatever Ken's engine was?
05-29-2016, 10:25 PM
#64
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As no doubt everyone with a Porkensioner, I've been reading these threads with great interest. My shop was unaware of the Porkensioner until they began working with my car back in 2011, but they now think it is an ingenious device that is easy and intuitive for them to deal with. It may help that they work on a fair share of Audis as well. They did me a new belt last spring and once again it was a great success and easy for them to deal with. It's surprising that there are engines that it doesn't work well on, getting overextended. Now we're all paranoid that the Porkensioner extension is the new flexplate endplay measurement, needing to be fretted about and checked all the time.
05-30-2016, 04:07 AM
#65
Rennlist Member
That's really not a bad idea. Maybe not so much about gathering data, but more about prompting us to measure how far the piston has extended. I check belt play once a year, but I've never given a second thought about checking the piston length.
fwiw, if I was PorKen, I'd probably change the text on page 7 to something like "Periodically check the extension of the piston using the instructions on page 5. If it ever exceeds 11 mm, immediately... " http://liftbars.com/docs/PKsnr.pdf
fwiw, if I was PorKen, I'd probably change the text on page 7 to something like "Periodically check the extension of the piston using the instructions on page 5. If it ever exceeds 11 mm, immediately... " http://liftbars.com/docs/PKsnr.pdf
05-30-2016, 07:46 AM
#66
Rennlist Member
I think the best idea is for everyone with a PKT to take some time and measure the extension. This is the only way that we can get the big picture. Will need to record all the data. ie: date of install, milage, belt type, any engine mods, climate factors. etc.
Pics would be great too.
I also believe that there is a way to measure extension by using a picture. as long as everyone takes it from the same angle.
Ken can post a procedure so that everyone is getting results based on a set procedure.
Pics would be great too.
I also believe that there is a way to measure extension by using a picture. as long as everyone takes it from the same angle.
Ken can post a procedure so that everyone is getting results based on a set procedure.
05-30-2016, 08:28 AM
#67
Rennlist Member
Thread Starter
I think the best idea is for everyone with a PKT to take some time and measure the extension. This is the only way that we can get the big picture. Will need to record all the data. ie: date of install, milage, belt type, any engine mods, climate factors. etc.
Pics would be great too.
I also believe that there is a way to measure extension by using a picture. as long as everyone takes it from the same angle.
Ken can post a procedure so that everyone is getting results based on a set procedure.
Pics would be great too.
I also believe that there is a way to measure extension by using a picture. as long as everyone takes it from the same angle.
Ken can post a procedure so that everyone is getting results based on a set procedure.
05-30-2016, 11:47 AM
#69
Rennlist Member
i wasn't aware of the Aussie race car...but good to know those two instances resulted in a change.
Agreed, on that initial measurement issue. That seems weird.
Agreed, on that initial measurement issue. That seems weird.
Two that I know of, plus Hai's however you want to count it. (The belt jumped a bunch of teeth, clearly a tension issue, with a PKT doing the tensioning... Call it what you want).
One was Jim M's GTS, the PKT dismounted itself from the block with a fractured M8 flathead, the two M8 flange-heads that unscrewed themselves (one completely, one partially), and the two plates that make up the bracket separated. There is no definitive evidence for which happened first.
The second was the tension pulley leaving the bracket on an Aussie race car, on the track. The M8 fastener fractured.
These two events led to the "black" version.
Whatever issues there might be with the PKT, I don't think that is one of them. Gates belts tend to stretch a bit during the first 1000-2000 miles, then settle down-- you can see this clearly when checking belt tension on a stock tensioner. So clearly if the limit is 9mm for a run-in belt then some margin is needed when new, but what that is will have to come from Ken. He originally said 2 - 7mm for a new belt, and 2 - 9mm for a used belt.
We put 70K on an early PKT on our GT: 50K then a belt change and a new roller/lever, then another 20K before swapping back to stock in late 2013. The initial extension was over 7mm (around 7.5 mm) for new belts, so I queried Ken and he said "fuggetaboutit" so we did. It didn't change appreciably further but I also did not make careful measurements after that-- it was billed as a install-and-forget-about-it device.
The concern is the initial measurement. Why would an engine with new/good gears and pulleys, and absent machined heads, be any different than whatever Ken's engine was?
One was Jim M's GTS, the PKT dismounted itself from the block with a fractured M8 flathead, the two M8 flange-heads that unscrewed themselves (one completely, one partially), and the two plates that make up the bracket separated. There is no definitive evidence for which happened first.
The second was the tension pulley leaving the bracket on an Aussie race car, on the track. The M8 fastener fractured.
These two events led to the "black" version.
Whatever issues there might be with the PKT, I don't think that is one of them. Gates belts tend to stretch a bit during the first 1000-2000 miles, then settle down-- you can see this clearly when checking belt tension on a stock tensioner. So clearly if the limit is 9mm for a run-in belt then some margin is needed when new, but what that is will have to come from Ken. He originally said 2 - 7mm for a new belt, and 2 - 9mm for a used belt.
We put 70K on an early PKT on our GT: 50K then a belt change and a new roller/lever, then another 20K before swapping back to stock in late 2013. The initial extension was over 7mm (around 7.5 mm) for new belts, so I queried Ken and he said "fuggetaboutit" so we did. It didn't change appreciably further but I also did not make careful measurements after that-- it was billed as a install-and-forget-about-it device.
The concern is the initial measurement. Why would an engine with new/good gears and pulleys, and absent machined heads, be any different than whatever Ken's engine was?
05-30-2016, 01:15 PM
#70
Inventor
Rennlist Member
Rennlist Member
I know it is human nature to be anxious but it bears reminding that PKTs have been run for hundreds of thousands of combined miles without issue if the recommendations were followed. (Millions if you include the native Audi installations.)
I have no idea why some engines are smaller from the factory. Casting differences, factory head machining, line boring...I don't know. Y'all figure it out. AFAIK, the T/D modification has worked for the handful of people who are 'lucky' enough to have these engines.
The current T/D spacing was made to allow stringing the belt with the T/D installed on most engines. This is easy enough to change. What is interesting is the PKT-B revision and this one, if it happens, would bring the bracket design back to that of the prototypes, which had through-bolts and a tight extension, but these features were changed to make it easier to install. Which is the whole point, really. I made a product in good faith that was meant to make 928 ownership a little easier. I would say it has worked extremely well given the limitations, both of the installation constraints and the designer's budget, but for a few isolated cases. There may well be a PKT-B1 or C with less initial T/D extension but only if there is demand for it.
I will not be posting much if anything in these threads going forward. There is a limit to how time I can spend reading the same topics over and over, I have nothing more to add, and there is only so much that can be done to improve the PKT to everyone's satisfaction.
I have no idea why some engines are smaller from the factory. Casting differences, factory head machining, line boring...I don't know. Y'all figure it out. AFAIK, the T/D modification has worked for the handful of people who are 'lucky' enough to have these engines.
The current T/D spacing was made to allow stringing the belt with the T/D installed on most engines. This is easy enough to change. What is interesting is the PKT-B revision and this one, if it happens, would bring the bracket design back to that of the prototypes, which had through-bolts and a tight extension, but these features were changed to make it easier to install. Which is the whole point, really. I made a product in good faith that was meant to make 928 ownership a little easier. I would say it has worked extremely well given the limitations, both of the installation constraints and the designer's budget, but for a few isolated cases. There may well be a PKT-B1 or C with less initial T/D extension but only if there is demand for it.
I will not be posting much if anything in these threads going forward. There is a limit to how time I can spend reading the same topics over and over, I have nothing more to add, and there is only so much that can be done to improve the PKT to everyone's satisfaction.
05-30-2016, 01:49 PM
#71
Rennlist Member
I know it is human nature to be anxious but it bears reminding that PKTs have been run for hundreds of thousands of combined miles without issue if the recommendations were followed. (Millions if you include the native Audi installations.)
I have no idea why some engines are smaller from the factory. Casting differences, factory head machining, line boring...I don't know. Y'all figure it out. AFAIK, the T/D modification has worked for the handful of people who are 'lucky' enough to have these engines.
The current T/D spacing was made to allow stringing the belt with the T/D installed on most engines. This is easy enough to change. What is interesting is the PKT-B revision and this one, if it happens, would bring the bracket design back to that of the prototypes, which had through-bolts and a tight extension, but these features were changed to make it easier to install. Which is the whole point, really. I made a product in good faith that was meant to make 928 ownership a little easier. I would say it has worked extremely well given the limitations, both of the installation constraints and the designer's budget, but for a few isolated cases. There may well be a PKT-B1 or C with less initial T/D extension but only if there is demand for it.
I will not be posting much if anything in these threads going forward. There is a limit to how time I can spend reading the same topics over and over, I have nothing more to add, and there is only so much that can be done to improve the PKT to everyone's satisfaction.
I have no idea why some engines are smaller from the factory. Casting differences, factory head machining, line boring...I don't know. Y'all figure it out. AFAIK, the T/D modification has worked for the handful of people who are 'lucky' enough to have these engines.
The current T/D spacing was made to allow stringing the belt with the T/D installed on most engines. This is easy enough to change. What is interesting is the PKT-B revision and this one, if it happens, would bring the bracket design back to that of the prototypes, which had through-bolts and a tight extension, but these features were changed to make it easier to install. Which is the whole point, really. I made a product in good faith that was meant to make 928 ownership a little easier. I would say it has worked extremely well given the limitations, both of the installation constraints and the designer's budget, but for a few isolated cases. There may well be a PKT-B1 or C with less initial T/D extension but only if there is demand for it.
I will not be posting much if anything in these threads going forward. There is a limit to how time I can spend reading the same topics over and over, I have nothing more to add, and there is only so much that can be done to improve the PKT to everyone's satisfaction.
05-30-2016, 03:24 PM
#72
Rennlist Member
Hi Jim,
I feel sorry for the OP but also for Ken. Maybe he's sold 1000 PK systems and 2 or 3 or so give out of spec extensions at time of install. I wouldn't know how to explain the outlying measurement either. I would offer to inspect the tensioner bracket for the customer (have him sign if first) and report the results. Due to the CNC laser cutting procedure, my guess is that is not the problem, but that should be verified. Then it would be the end user's responsibility to verify his motor's dimensions, somehow.
Since the PK system seems to work fine when installed with in spec extension, I would devise a strategy to deal with the few that fall out of spec. I really don't think that overbored holes and fastener friction to maintain eccentric position is adequate. Either provide an adjusted bracket or other method that will be just as durable for these outliers as for the majority of users. Or provide a refund for outliers, and recommend the stock system.
My own reaction might well be similar to Ken's, where I would emphasize how rare this problem is. After some thought, I would realize how bad it is for those who suffer from it, and try to deal with that with extra TLC.
Good luck,
Dave
I feel sorry for the OP but also for Ken. Maybe he's sold 1000 PK systems and 2 or 3 or so give out of spec extensions at time of install. I wouldn't know how to explain the outlying measurement either. I would offer to inspect the tensioner bracket for the customer (have him sign if first) and report the results. Due to the CNC laser cutting procedure, my guess is that is not the problem, but that should be verified. Then it would be the end user's responsibility to verify his motor's dimensions, somehow.
Since the PK system seems to work fine when installed with in spec extension, I would devise a strategy to deal with the few that fall out of spec. I really don't think that overbored holes and fastener friction to maintain eccentric position is adequate. Either provide an adjusted bracket or other method that will be just as durable for these outliers as for the majority of users. Or provide a refund for outliers, and recommend the stock system.
My own reaction might well be similar to Ken's, where I would emphasize how rare this problem is. After some thought, I would realize how bad it is for those who suffer from it, and try to deal with that with extra TLC.
Good luck,
Dave
05-30-2016, 03:38 PM
#73
Nordschleife Master
Hi Jim,
I feel sorry for the OP but also for Ken. Maybe he's sold 1000 PK systems and 2 or 3 or so give out of spec extensions at time of install. I wouldn't know how to explain the outlying measurement either. I would offer to inspect the tensioner bracket for the customer (have him sign if first) and report the results. Due to the CNC laser cutting procedure, my guess is that is not the problem, but that should be verified. Then it would be the end user's responsibility to verify his motor's dimensions, somehow.
Since the PK system seems to work fine when installed with in spec extension, I would devise a strategy to deal with the few that fall out of spec. I really don't think that overbored holes and fastener friction to maintain eccentric position is adequate. Either provide an adjusted bracket or other method that will be just as durable for these outliers as for the majority of users. Or provide a refund for outliers, and recommend the stock system.
I feel sorry for the OP but also for Ken. Maybe he's sold 1000 PK systems and 2 or 3 or so give out of spec extensions at time of install. I wouldn't know how to explain the outlying measurement either. I would offer to inspect the tensioner bracket for the customer (have him sign if first) and report the results. Due to the CNC laser cutting procedure, my guess is that is not the problem, but that should be verified. Then it would be the end user's responsibility to verify his motor's dimensions, somehow.
Since the PK system seems to work fine when installed with in spec extension, I would devise a strategy to deal with the few that fall out of spec. I really don't think that overbored holes and fastener friction to maintain eccentric position is adequate. Either provide an adjusted bracket or other method that will be just as durable for these outliers as for the majority of users. Or provide a refund for outliers, and recommend the stock system.
05-30-2016, 03:44 PM
#74
Rennlist Member
Sorry,
Dave
05-30-2016, 03:53 PM
#75
Nordschleife Master
In a standard bolted interface, the hole is not supposed to tight for the bolt, it's supposed to be loose. Only "shoulder bolt" is tight in the hole and that's a different design from standard bolt.
That's why I believe precision located standard bolted interfaces have two dowels to locate the component in the x-y plane and then bolts in relatively loose holes to clamp the parts together. Dowels just make sure that the part is installed in the correct position and do zero percent of the holding once the bolts are tightened. For example, think of the early girdle to block interface, which was located by two dowel sleeves and the holes on studs were otherwise loose. (Later they dropped one dowel sleeve from the front when the revised nose main bearing locates one degree of freedom.) The dowel sleeve does nothing after the nuts have been tightened on the studs.
Now, this is just from my self education starting from the base of high school physics, so I may be wrong, but I think I'm not. So what's the problem with enlarging the hole, too little clamping surface? Or what?
