'87 S4 Timing Death
05-20-2016, 01:19 PM
#76
Captain Obvious
Super User
Super User
I used a very short aluminium pipe with the allen key and slowly compressed it. Made it easier on my hands since I had to re do a few times.
05-20-2016, 01:20 PM
#77
Team Owner
Put a regular belt on it and do a compression test
05-20-2016, 01:26 PM
#78
Former Sponsor
I'm going to go out on a limb and disagree a bit with Greg vis-a-vis the Belleville stack design.
First, the way I understand the Belleville stack is that it will maintain nearly constant tension under differing temp conditions. As the engine grows, the stock belt remains basically the same length(non-racing). The Belleville stack should compress slightly as the fluid in it heats up. This would be consistent with the known properties of the metal used(Inconel 7xx series?). It would also fit the application, as the tension generally goes up as the engine grows under increased temp. However, I agree that the stock tensioner does have a metal short-limiting length that cannot be shortened unless the adjustment pin is backed out.
Next, I think and am pretty sure that the hydraulic tensioners operate basically the same in that they are designed to compress gradually as the engine grows, and just the opposite, in that they will expand or more accurately extend fairly rapidly to take up any slack under differing throttle loads where slack would tend to build up. This is consistent with where the tensioner is located at the end of the driven loop of the circuit and just before the drive end(crank). So it operates kind of like a shock absorber with a high deflect ratio for off road use.
I removed the small roller cartridge off both of my 928s, but retained the stock tensioner. My decision was based primarily on the extremely low failure rate of a properly maintained and adjusted stock tensioner.
First, the way I understand the Belleville stack is that it will maintain nearly constant tension under differing temp conditions. As the engine grows, the stock belt remains basically the same length(non-racing). The Belleville stack should compress slightly as the fluid in it heats up. This would be consistent with the known properties of the metal used(Inconel 7xx series?). It would also fit the application, as the tension generally goes up as the engine grows under increased temp. However, I agree that the stock tensioner does have a metal short-limiting length that cannot be shortened unless the adjustment pin is backed out.
Next, I think and am pretty sure that the hydraulic tensioners operate basically the same in that they are designed to compress gradually as the engine grows, and just the opposite, in that they will expand or more accurately extend fairly rapidly to take up any slack under differing throttle loads where slack would tend to build up. This is consistent with where the tensioner is located at the end of the driven loop of the circuit and just before the drive end(crank). So it operates kind of like a shock absorber with a high deflect ratio for off road use.
I removed the small roller cartridge off both of my 928s, but retained the stock tensioner. My decision was based primarily on the extremely low failure rate of a properly maintained and adjusted stock tensioner.
Regardless of what the Belleville washers do, the stock tensioner can't be compressed much...if any.
However, if the Audi design tensioner fails internally and the plunger returns, the "gig" is instantly over.
05-20-2016, 01:37 PM
#79
Pro
Thread Starter
Which brings me to the "what do I do now" point.
I like the idea of sourcing a stock Gates belt, installing it, and checking compression (and observing how far the Audi tensioner extends). Costs me a belt and some time.
I am a lucky SOB, though it seems ridiculous to think valves aren't bent and this thing will have good compression/run. I had a later 9-3 come in with the intake came nearly 180 degrees off thanks to the power steering pump it drives...replaced the broken pump, reset the cam timing, and it ran perfectly. Yes they are interference engines.
I like the idea of sourcing a stock Gates belt, installing it, and checking compression (and observing how far the Audi tensioner extends). Costs me a belt and some time.
I am a lucky SOB, though it seems ridiculous to think valves aren't bent and this thing will have good compression/run. I had a later 9-3 come in with the intake came nearly 180 degrees off thanks to the power steering pump it drives...replaced the broken pump, reset the cam timing, and it ran perfectly. Yes they are interference engines.
05-20-2016, 01:40 PM
#80
Inventor
Rennlist Member
Rennlist Member
"With a new belt, extension must be > 2mm, and < 7mm. A used belt must be > 2mm and < 9mm. Maximum extension is 11mm. An engine with machined heads may be close to 9mm. With a used belt on a cold engine, on a cold day, extension must never be more than 11mm!"
The Racing belt does eventually stretch a little bit, so when the engine was cold there was no range left, unfortunately.
05-20-2016, 01:46 PM
#81
Captain Obvious
Super User
Super User
The last page of the PKT manual has a procedure for dealing with an installed measurement of 9mm (machined heads).
"With a new belt, extension must be > 2mm, and < 7mm. A used belt must be > 2mm and < 9mm."
I concur.
Too much initial extension. The Racing belt does eventually stretch a little bit, so when the engine was cold there was no range left (max 11).
"With a new belt, extension must be > 2mm, and < 7mm. A used belt must be > 2mm and < 9mm."
I concur.
Too much initial extension. The Racing belt does eventually stretch a little bit, so when the engine was cold there was no range left (max 11).
05-20-2016, 01:50 PM
#83
Team Owner
I was also wondering since this is a 5 speed car since just before the failure,
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
05-20-2016, 01:54 PM
#84
Rennlist Member
Wow, figure I'd add this as I see some have asked the question.
I have been running the Gates Racing belt w. PkTensioner and no lower rollers on 2 cars.
One has 150 hp power added via N02 and has had no issues over 5k miles ad a few years now, another has run several track events and has Ken's S300's and about 2k street miles.
There is also a Murf SC car (over 500 whp) w/ the Pk Tensioner and no lower rollers that I put together over 4 years ago w/ no T-belt issues. Many long trips to WV and NC and lots of
I always remove the lower rollers as w/ the Audi tensioner they are just a place to gum up the belt travel IMO, no longer needed/required and were put there to support the short comings of the Stock Tensioner.
Has anyone looked at the Cam Chains and those tensioners yet?
Also I agree that belt is tracking too far rearward and the WP would do that IIRC.
Dave
Edit: just read about over extension, so was that proven to be the cause and the belt got too loose?
I have been running the Gates Racing belt w. PkTensioner and no lower rollers on 2 cars.
One has 150 hp power added via N02 and has had no issues over 5k miles ad a few years now, another has run several track events and has Ken's S300's and about 2k street miles.
There is also a Murf SC car (over 500 whp) w/ the Pk Tensioner and no lower rollers that I put together over 4 years ago w/ no T-belt issues. Many long trips to WV and NC and lots of
I always remove the lower rollers as w/ the Audi tensioner they are just a place to gum up the belt travel IMO, no longer needed/required and were put there to support the short comings of the Stock Tensioner.
Has anyone looked at the Cam Chains and those tensioners yet?
Also I agree that belt is tracking too far rearward and the WP would do that IIRC.
Dave
Edit: just read about over extension, so was that proven to be the cause and the belt got too loose?
05-20-2016, 02:06 PM
#85
Inventor
Rennlist Member
Rennlist Member
I should have been more forceful in recommending that the tensioner/damper be modified because of the milled heads. I did not know at the time that the Racing belt does stretch slightly but it takes much longer to do so.
https://rennlist.com/forums/928-foru...l#post10585389
05-20-2016, 02:11 PM
#86
Pro
Thread Starter
I was also wondering since this is a 5 speed car since just before the failure,
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
05-20-2016, 02:14 PM
#87
Rennlist Member
My concern is that if you park it hot, then let it sit and cool off, the belt goes slack. The spring pressure in the tensioner is not strong enough to rotate the cams, all it can do (with the engine stopped) is take up the slack that develops between the crank and the 1/4 cam.
In theory, as soon as the starter begins cranking on a cold start then the crank gear moves the slack to the tensioner side where it gets taken up. But without tension on the "upstream" part of the belt, what's to keep the belt from popping out of the gear and riding on top of the gear teeth for a while?
No.
05-20-2016, 02:18 PM
#88
Pro
Thread Starter
I was also wondering since this is a 5 speed car since just before the failure,
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
any chance it was parked on a slight hill tail down when it was hot,
and just the transmission was used to hold it in park.
This could have let the crank turn backwards thus compressing the tensioner to its full compression and then when it was started the belt teeth being more loose than a regular belt simply slipped off the crank till the tensioner caught up with the belt
OR do you use the e brake every time and is it adjusted properly and used without fail?
Maybe a better question how do you park your car?
The aged crank gear may have played a minor role. Not sure that the rollers would have helped.
I should have been more forceful in recommending that the tensioner/damper be modified because of the milled heads. I did not know at the time that the Racing belt does stretch slightly but it takes much longer to do so.
https://rennlist.com/forums/928-foru...l#post10585389
I should have been more forceful in recommending that the tensioner/damper be modified because of the milled heads. I did not know at the time that the Racing belt does stretch slightly but it takes much longer to do so.
https://rennlist.com/forums/928-foru...l#post10585389
05-20-2016, 02:19 PM
#89
Rennlist Member
The aged crank gear may have played a minor role. Not sure that the rollers would have helped.
I should have been more forceful in recommending that the tensioner/damper be modified because of the milled heads. I did not know at the time that the Racing belt does stretch slightly but it takes much longer to do so.
https://rennlist.com/forums/928-foru...l#post10585389
I should have been more forceful in recommending that the tensioner/damper be modified because of the milled heads. I did not know at the time that the Racing belt does stretch slightly but it takes much longer to do so.
https://rennlist.com/forums/928-foru...l#post10585389
05-20-2016, 02:20 PM
#90
Addict
Rennlist Member
Rennlist Member
In theory, as soon as the starter begins cranking on a cold start then the crank gear moves the slack to the tensioner side where it gets taken up. But without tension on the "upstream" part of the belt, what's to keep the belt from popping out of the gear and riding on top of the gear teeth for a while?
That's essentially my theory. The engine is stopped with the valvesprings tugging on the tensioner side of the belt. The tensioner slowly retracts and more slack collects on the drive side. Upon start, the slack causes some belt whip at the crank sprocket and jumped time.