'87 S4 Timing Death
05-27-2016, 02:39 PM
#331
Rennlist Member
I think it is the perfect metaphor. It is often said the stock system is so robust. Never has a problem when adjusted properly. Runs without oil. This is because the stock tensioner does not do anything except to limit the expected total length of the timing belt. Once the engine is running (and warm), the belt and the guide pulleys run the show.
With the arrival of the 32V, the increased load makes for an even longer belt at times so the pre-tension level was raised in order to further reduce the possible stretched length of the belt at the cost of higher parasitic losses and wear.
In comparison, the PKT actively manages the belt so it does not need to pre-stretch the belt in order to control its length.
I should have said 'and warm', but inaccurate, no. When the engine is cold the uneven torque pulses are somewhat dampened by the extended washer stack and the hydraulic system. By design, once the stack has flattened the tensioner is fixed. There is no spring to rebound and consequently no dampening.
This cold dampening may explain the thinking behind the 3 minute tension light delay at startup. The process of dampening may have caused the light to come on in testing.
In the beginning...this may have been partially true. I have come to understand the stock system and while I still think it is crude, apparently it does work if adjusted well enough. Of course this is because of how strong timing belts are, not by virtue of the stock system.
I 'admitted' the shortcoming of the PKT in a previous post. The obvious problem of being too far extended to do it's job. This is a rare event and I imagine there were other factors, but I will change the specs in the manual to recommend always being on the lower end of piston travel when installing.
With the arrival of the 32V, the increased load makes for an even longer belt at times so the pre-tension level was raised in order to further reduce the possible stretched length of the belt at the cost of higher parasitic losses and wear.
In comparison, the PKT actively manages the belt so it does not need to pre-stretch the belt in order to control its length.
I should have said 'and warm', but inaccurate, no. When the engine is cold the uneven torque pulses are somewhat dampened by the extended washer stack and the hydraulic system. By design, once the stack has flattened the tensioner is fixed. There is no spring to rebound and consequently no dampening.
This cold dampening may explain the thinking behind the 3 minute tension light delay at startup. The process of dampening may have caused the light to come on in testing.
In the beginning...this may have been partially true. I have come to understand the stock system and while I still think it is crude, apparently it does work if adjusted well enough. Of course this is because of how strong timing belts are, not by virtue of the stock system.
I 'admitted' the shortcoming of the PKT in a previous post. The obvious problem of being too far extended to do it's job. This is a rare event and I imagine there were other factors, but I will change the specs in the manual to recommend always being on the lower end of piston travel when installing.
with that said, the PK tensioner maybe reduces cold start up wear.
Ken, I haven't studied the internals of the Audi piston assembly. Is it coil-spring with hydraulic dampening, or is there something else that adds hydraulic pressure to pressure the piston?
We continue to refer to the Audi piston as "hydraulic"; I suspect its a coil spring to tension with hydraulic dampening. You've studied this a lot obviously a lot more than I have (none...). I'm much more familiar with chain tensioners, which have a hydraulic piston, a latching mechanism to limit retraction as the chain ages, with the piston supplied engine oil pressure via a restriction orifice. Many hydraulic belt tensioning systems have used this method.
Anyway, what provides the piston pressure in the Audi tensioner?
We continue to refer to the Audi piston as "hydraulic"; I suspect its a coil spring to tension with hydraulic dampening. You've studied this a lot obviously a lot more than I have (none...). I'm much more familiar with chain tensioners, which have a hydraulic piston, a latching mechanism to limit retraction as the chain ages, with the piston supplied engine oil pressure via a restriction orifice. Many hydraulic belt tensioning systems have used this method.
Anyway, what provides the piston pressure in the Audi tensioner?
Stock tensioner + lower rollers + stock Gates belt = good
Stock tensioner - lower rollers + racing belt = good
Stock tensioner + lower rollers + racing belt = questionable(rubs)
Pkentioner + lower rollers + stock Gates belt = good
Pkentioner - lower rollers + any belt = bad
Pkentioner + lower rollers + racing belt = bad(still rubs)
For someone who has never even seen a PKT or used a Gates Racing TB you sure are full of S**t.
Stock tensioner - lower rollers + racing belt = good
Stock tensioner + lower rollers + racing belt = questionable(rubs)
Pkentioner + lower rollers + stock Gates belt = good
Pkentioner - lower rollers + any belt = bad
Pkentioner + lower rollers + racing belt = bad(still rubs)
For someone who has never even seen a PKT or used a Gates Racing TB you sure are full of S**t.
never had any issues at all......
And has a zero failure potential!
The stock tensioner isn't going to fail....unless it falls off the front of the engine.
You keep (conveniently) skipping over this point.
You can rationalize what you built all you want...how you think it works better as the engine warms up. How you think it better controls the belt.
But the reality is that the OP wouldn't have a pile of scrap metal if he had installed the original tensioner.
The stock tensioner isn't going to fail....unless it falls off the front of the engine.
You keep (conveniently) skipping over this point.
You can rationalize what you built all you want...how you think it works better as the engine warms up. How you think it better controls the belt.
But the reality is that the OP wouldn't have a pile of scrap metal if he had installed the original tensioner.
on think I mentioned a long time ago to provide a simple tension test that would ball park the tension in the 3-6 tension setting range, was a small hole drilled in the removable timing belt upper cover. this small hole i pushed a small metal dowel into the hole and pressed on the belt. as hard as i could push it, I made a mark on the dowel (or drill bit put in dull side in). I just did this the other day with my new stock conti belt after a race weekend laguna , before i went to willow springs.. it felt good, but a little questionable past the mark i made... so i pulled the cover.... the Kempf tensioner said "all go" right in the middle of the window, but the 9201 tool, said 3.2.... so, a .25 turn and it was at 5 and off i went to the races. Point is, checking this way to make sure you dont have a real problem is easy and effective.
05-27-2016, 02:46 PM
#332
Former Sponsor
The problem with the stock tensioner system is that in order for it to keep the belt wrapped around the gears in the worst case geometry change scenario it needs so much extension and pre-tension that in the other end of the geometry change scenarios the belt is over tensioned and wears out cam gears, breaks cams, snaps belts, and seizes water pumps. Although the stupid warning light in the stock system combined with bad choices by people is responsible for many of the catastrophic failures, it's still the case that even when maintained exactly optimally the stock system wears out expensive components and requires frequent replacement of parts (or risking catastrophic failure). The reputation of the 928 engine timing belt system as the Achilles's heel of the car didn't just appear from thin air.
I think you are correct about improving the PKT-B instructions. There should be instructions about what exactly to do if the tensioner extension is not within the tolerance range. How much can the bracket be adjusted and how should it be done? I'm sure that Ken will respond to honest and constructive criticism, in contrast to just spreading FUD or calling his product names.
Considering the forces acting on this tensioner system and taking a look at the hardware (http://liftbars.com/docs/PKT-B_bolts.pdf), I think that if the tensioner is not pegging at the minimum extension it will be very hard for the braket or fasteners to break. Just my opinion.
I think you are correct about improving the PKT-B instructions. There should be instructions about what exactly to do if the tensioner extension is not within the tolerance range. How much can the bracket be adjusted and how should it be done? I'm sure that Ken will respond to honest and constructive criticism, in contrast to just spreading FUD or calling his product names.
Considering the forces acting on this tensioner system and taking a look at the hardware (http://liftbars.com/docs/PKT-B_bolts.pdf), I think that if the tensioner is not pegging at the minimum extension it will be very hard for the braket or fasteners to break. Just my opinion.
I offer this as a contrary opinion....purely to "counteract" statements which become "Internet Myths" if not corrected.
Cam gear wear is a natural occurrence, due to the original design and coating. With a correctly adjusted, well maintained belt, they will last about 80,000 miles. With a loose belt, they will last about 80,000 miles.
Water pump failures from bearing failures are extremely low in number....I can **** them on one hand, in all the years I've worked on these cars....and that number is certainly no higher than people experience with the new water cooled Porsches. Water pump seals fail and the hot steaming water cleans the grease out of the bearing in mere minutes.....it's the nature of the beast.
I've never, ever seen a snapped belt....even with all the idiots that have installed the belts.
I've never, ever seen a snapped off cam on a 32 valve engine from a timing belt being over tightened. I've seen two broken cam drive hubs cracking and failing, from the cam bolt not being properly torqued.
I've seen hundreds of cars with the original cam belts installed on them, with over 60,000 miles....performing flawlessly. I've seen hundreds of cars with an original belt that was 25+ years old. Literally hundreds of each.
I've seen dozens of cars with the cam gears worn through so far that you can literally see air through them....dozens. Without a single belt failure resulting in engine damage.
I'd submit that the "bad design belt problems" with the 928 models came after the first belt change was performed....by an idiot.
05-27-2016, 02:55 PM
#333
Former Sponsor
And that has what exactly to do with this thread? You and the other folks that keep posting about the stock tensioner only clog up this thread.
I never sent a sample PKT to Mark (but I did send a PK32V'r). He asked me about selling them and directed me to talk to you.
It was only later that I realized that this request was done at your behest, just so that you could try to gather information to trash the PKT.
It writes itself. You show your ignorance each time you post, even when you are not making stuff up.
I never sent a sample PKT to Mark (but I did send a PK32V'r). He asked me about selling them and directed me to talk to you.
It was only later that I realized that this request was done at your behest, just so that you could try to gather information to trash the PKT.
It writes itself. You show your ignorance each time you post, even when you are not making stuff up.
I'm not the one with a customer that just trashed his engine with my product....
I'm not the one looking at my third major engine failure in a very small sample of units sold....
I am the one that has installed thousands of stock belts with stock tensioners and stock pieces.....who has never, ever, had a single one of those engines come back for a failure. Zero. Nada.
If that is me being ignorant, I'm fantastic with it!
05-27-2016, 03:07 PM
#334
Inventor
Rennlist Member
Rennlist Member
The point is you are clogging up this thread with your blustering and spreading misinformation.
An engine that may have bent valves that has a PKT installed. As yet, correlation, not causation.
That is your native enviroment (to both statements). You are allegedly a great mechanic. Plenty of experience. Unfortunately you have repeatably shown that you have no capacity for original thought. And, what you don't understand you trash and bully. Witness the PKT, the PK32V'r, or any other person's products.
One confirmed engine with bent valves, due to hardware, not the Audi parts. This engine was repaired and a PKT refitted.
One confirmed engine with bent valves, due to hardware, not the Audi parts. This engine was repaired and a PKT refitted.
05-27-2016, 03:41 PM
#335
Former Sponsor
With respect to my customer requests for the replacement lower roller/rollers - most call and say that the roller/rollers are seized. Once I quote the replacement $250 - large intake of breath - I offer the bearing for $9.95 each.
Checking sales of that bearing and I have sold 66 in the last 12 months. Some of those would have been a two bearing sale. So rough guess 50 cars. Tells me my own experience with seized bearings is echoed out there in 928 land as well.
Checking sales of that bearing and I have sold 66 in the last 12 months. Some of those would have been a two bearing sale. So rough guess 50 cars. Tells me my own experience with seized bearings is echoed out there in 928 land as well.
Responce to your ideas about the lower roller:
Here's a picture of a very typical double roller....I just removed this from an engine I'm rebuilding, yesterday.
I talked about the operation of the second roller in post 227.....and the problems of why they discontinued it. (Noise.)
You can clearly see that the right hand roller touches the belt....often.
And the left hand roller touches the belt infrequently.
The left hand roller always has "skid marks' where the has contacted it very hard....but since it doesn't touch the belt on an everyday basis, it does collect dirt and does get gummed up. I'd submit that this roller is there for one reason....to prevent the "Perfect Storm".....to keep the belt from jumping cam timing. Yes, these rollers are frequently "gummed up" and may not turn because the grease is hard, but almost every single one will turn and feel perfect, with just a tiny bit of "exercise"....and every single one will have those "significant" hit marks when it was needed to keep the engine from skipping cam timing.
The right hand roller, in my opinion, was put there to help control the slight "flopping" of the belt on the non-tensioned side of the belt to better feed the belt into the crankshaft drive hub. The problem with this roller is that it contacted the belt way too much and was noisy, in many vehicles....so they went back to the primary purpose...to keep the cam belt from jumping on the crank drive gear, with the single roller.
A cam belt without a lower roller may not instantly spell disaster....having to wait until the conditions are just perfect for failure....but it is certainly "playing against the odds" way more than anyone should do.
Put those rollers back in place....very bad advice.
05-27-2016, 04:16 PM
#337
Pro
Thread Starter
When I explained what seems to have happened (belt came out of crank gear) and told him about the tensioner extension issue, he immediately suggested a lash cap for the tensioner rod. He was then distraught that I had removed the safety mechanism of the rollers below the crank gear.
05-27-2016, 04:22 PM
#338
Inventor
Rennlist Member
Rennlist Member
The trouble with a lash cap is that the T/D piston rounded because it is only perpendicular to the lever in one position.
Last edited by PorKen; 05-27-2016 at 04:40 PM. Reason: perpendicular
05-27-2016, 04:38 PM
#339
Rennlist Member
05-27-2016, 04:38 PM
#340
Rennlist Member
Roger:
Responce to your ideas about the lower roller:
Here's a picture of a very typical double roller....I just removed this from an engine I'm rebuilding, yesterday.
I talked about the operation of the second roller in post 227.....and the problems of why they discontinued it. (Noise.)
You can clearly see that the right hand roller touches the belt....often.
And the left hand roller touches the belt infrequently.
The left hand roller always has "skid marks' where the has contacted it very hard....but since it doesn't touch the belt on an everyday basis, it does collect dirt and does get gummed up. I'd submit that this roller is there for one reason....to prevent the "Perfect Storm".....to keep the belt from jumping cam timing. Yes, these rollers are frequently "gummed up" and may not turn because the grease is hard, but almost every single one will turn and feel perfect, with just a tiny bit of "exercise"....and every single one will have those "significant" hit marks when it was needed to keep the engine from skipping cam timing.
The right hand roller, in my opinion, was put there to help control the slight "flopping" of the belt on the non-tensioned side of the belt to better feed the belt into the crankshaft drive hub. The problem with this roller is that it contacted the belt way too much and was noisy, in many vehicles....so they went back to the primary purpose...to keep the cam belt from jumping on the crank drive gear, with the single roller.
A cam belt without a lower roller may not instantly spell disaster....having to wait until the conditions are just perfect for failure....but it is certainly "playing against the odds" way more than anyone should do.
Put those rollers back in place....very bad advice.
Responce to your ideas about the lower roller:
Here's a picture of a very typical double roller....I just removed this from an engine I'm rebuilding, yesterday.
I talked about the operation of the second roller in post 227.....and the problems of why they discontinued it. (Noise.)
You can clearly see that the right hand roller touches the belt....often.
And the left hand roller touches the belt infrequently.
The left hand roller always has "skid marks' where the has contacted it very hard....but since it doesn't touch the belt on an everyday basis, it does collect dirt and does get gummed up. I'd submit that this roller is there for one reason....to prevent the "Perfect Storm".....to keep the belt from jumping cam timing. Yes, these rollers are frequently "gummed up" and may not turn because the grease is hard, but almost every single one will turn and feel perfect, with just a tiny bit of "exercise"....and every single one will have those "significant" hit marks when it was needed to keep the engine from skipping cam timing.
The right hand roller, in my opinion, was put there to help control the slight "flopping" of the belt on the non-tensioned side of the belt to better feed the belt into the crankshaft drive hub. The problem with this roller is that it contacted the belt way too much and was noisy, in many vehicles....so they went back to the primary purpose...to keep the cam belt from jumping on the crank drive gear, with the single roller.
A cam belt without a lower roller may not instantly spell disaster....having to wait until the conditions are just perfect for failure....but it is certainly "playing against the odds" way more than anyone should do.
Put those rollers back in place....very bad advice.
05-27-2016, 04:44 PM
#341
Inventor
Rennlist Member
Rennlist Member
Meant to say perpendicular in one position only. The lever contacts the piston at different points on the tip of the piston as it moves.
Plus, obviously the lash cap has to be wider than the piston to fit over it so it would change the contact point to the inside changing the ratio.
Plus, obviously the lash cap has to be wider than the piston to fit over it so it would change the contact point to the inside changing the ratio.
05-27-2016, 04:50 PM
#342
Inventor
Rennlist Member
Rennlist Member
Snake Plissken. I thought you were dead!
Gawd. Now Kibort?
Sigh. All of that is incorrect wrong.
Yes, i dont run any oil. (just a coating of the parts internal to prevent rust. i think the only function of the oil is for distributing heat to the discs for tension adjustment so that when you are running "flat out" the tension is correct. i just wait a little longer before i do this with my engine . the heat transfers, just takes a little longer.
with that said, the PK tensioner maybe reduces cold start up wear.
with that said, the PK tensioner maybe reduces cold start up wear.
05-27-2016, 04:53 PM
#343
Rennlist Member
Meant to say perpendicular in one position only. The lever contacts the piston at different points on the tip of the piston as it moves.
Plus, obviously the lash cap has to be wider than the piston to fit over it so it would change the contact point to the inside changing the ratio.
Plus, obviously the lash cap has to be wider than the piston to fit over it so it would change the contact point to the inside changing the ratio.
05-27-2016, 04:56 PM
#344
Captain Obvious
Super User
Super User
05-27-2016, 04:56 PM
#345
Inventor
Rennlist Member
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