Things everyone should know about 928 Engine Thrust Bearing Failure
05-27-2010, 02:33 AM
#31
Former Sponsor
I had that block surfaced and then align bored back to standard size. Keep in mind that when doing this to one of these blocks, the oil pump bore, the front seal bore, and the rear seal bore also have to be bored back to original dimensions.
In short, you are not likely to never see a block that can be salvaged and if you do decide to salvage it, it will cost a ton to fix.
05-27-2010, 02:38 AM
#32
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Hi Everyone,
I am new to this forum but not the 928.
I have just bought a '87 928 S4 with a dead engine and here is what has happened:
Problem= The crankshaft has a failed thrust bearing.
Cause= It appears that virtually all 928's, particularly automatics, have the driveshaft within the torque tube put excessive pressure on the flywheel/drive plate and this wears away the thust bearings inside the engine. In my case the wear was so excessive the crankshaft has worn into the internal faces of the block casting, and wrecked the engine! Please read this: http://members.rennlist.com/v1uhoh/cranksha.htm
My question is WHY does the driveshaft have a force pushing it into the engine, or WHAT IS GOING ON WITHIN THE GEARBOX THAT CREATES THIS??
Can anyone elaborate on the exact sequence of events that cause this problem??
PLEASE if you want to keep your engine safe CHECK THE PRESSURE ON YOUR DRIVE PLATE, it's a quick check and it may save you a new engine!!!
I am new to this forum but not the 928.
I have just bought a '87 928 S4 with a dead engine and here is what has happened:
Problem= The crankshaft has a failed thrust bearing.
Cause= It appears that virtually all 928's, particularly automatics, have the driveshaft within the torque tube put excessive pressure on the flywheel/drive plate and this wears away the thust bearings inside the engine. In my case the wear was so excessive the crankshaft has worn into the internal faces of the block casting, and wrecked the engine! Please read this: http://members.rennlist.com/v1uhoh/cranksha.htm
My question is WHY does the driveshaft have a force pushing it into the engine, or WHAT IS GOING ON WITHIN THE GEARBOX THAT CREATES THIS??
Can anyone elaborate on the exact sequence of events that cause this problem??
PLEASE if you want to keep your engine safe CHECK THE PRESSURE ON YOUR DRIVE PLATE, it's a quick check and it may save you a new engine!!!
you don't say....
..... 
05-27-2010, 09:28 PM
#34
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My own block did have a hairline crack but I decided to attempt a repair anyway. The refacing and line boring for the main bearings together with the additional boring for the oil pump and seals seemed to be a very big deal and quite expensive. Most shops would not even touch the job.
Instead, I had a shop just machine the damaged bearing bore until it was clean. The bore was now 0.018" oversize so I cut a pair of 0.009" steel shims to take up the difference (with suitable oil holes of course).
It was a little fiddly to reassemble but it worked.
To date I have over 5000 miles since the rebuild with many trips into the red zone on the tach and it is still holding together. Oh yes, one more thing - my TT shaft had the circlip groove so I installed the correct shims and clip etc to stop the flex plate from moving again. One TBF is enough for anyone!
Brian
Instead, I had a shop just machine the damaged bearing bore until it was clean. The bore was now 0.018" oversize so I cut a pair of 0.009" steel shims to take up the difference (with suitable oil holes of course).
It was a little fiddly to reassemble but it worked.
To date I have over 5000 miles since the rebuild with many trips into the red zone on the tach and it is still holding together. Oh yes, one more thing - my TT shaft had the circlip groove so I installed the correct shims and clip etc to stop the flex plate from moving again. One TBF is enough for anyone!
Brian
05-27-2010, 10:56 PM
#35
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I drive my car like the daily driver that it is. I had my thrust bearing pressure checked last fall while I was down in Panama City, FL by a very reputable shop. They saw no issue with it. That said, would a daily driver be as suseptible to TBF as the every weekend "drive it like you stole it" driver?
05-28-2010, 12:36 AM
#36
Captain Obvious
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This was done on an '87 S4. The face of the damaged area was machined down and a spacer (looked like a big washer) was cut in half and intalled behind a new thrust bearing. The new bearing was an early 32V thrust bearings, as they apperanlty have a much larger face than the S4-up ones. This was done by a lister that was local to me and I've seen the engine a part and the machine work and spacer before it was installed. Then a few months later saw the finished product and it ran butifully. However I think he sold the car since, about a year or so after it was all back together, but not before putting at least a few thousand miles on it. He was an aircraft engineer so the repair and re assembly was very detailed.
05-28-2010, 01:26 AM
#37
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My friend the Immortal Mongo:
https://rennlist.com/forums/928-foru...g-failure.html
even though i walk through the valley of the shadow of death...
Okay to get some things straight about thrust bearing failure (yet again) or TBF. Please read below:
1. Thrust Bearing Failure is Possible on 928s.
-True
2. Thrust Bearing Failure happens on ALL 928s.
-False
3. There is a chance TBF will happen on a 928 that has had the torque tube replaced if torquing procedures of the pinch collar weren't adhered to.
-True
4. It takes 1-2 hours depending on how slow, drunk, lazy, tired, or any other chronic or hypochondric condition you are in to check and release the end play of the flex plate by dropping the exhaust and belly pans ONCE A YEAR.
-True
5. There is way too much SCARE about thrust bearing failure on 928s in this forum.
TRUE, TRUE, and TRUE.
Thank you for reading
1. Thrust Bearing Failure is Possible on 928s.
-True
2. Thrust Bearing Failure happens on ALL 928s.
-False
3. There is a chance TBF will happen on a 928 that has had the torque tube replaced if torquing procedures of the pinch collar weren't adhered to.
-True
4. It takes 1-2 hours depending on how slow, drunk, lazy, tired, or any other chronic or hypochondric condition you are in to check and release the end play of the flex plate by dropping the exhaust and belly pans ONCE A YEAR.
-True
5. There is way too much SCARE about thrust bearing failure on 928s in this forum.
TRUE, TRUE, and TRUE.
Thank you for reading
https://rennlist.com/forums/928-foru...g-failure.html
even though i walk through the valley of the shadow of death...
05-28-2010, 04:41 AM
#38
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Idea that releasing clamp once a year will solve entire problem is simply stupid. If clamp moves back to 1-2mm preload next day after reseting it will mean bearing will be loaded next 364 days. TBF will follow soon enough.
05-28-2010, 06:32 AM
#39
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Thank you Erkka! Been saying this for a long time but not as direct.
And about there being too much "scare" about TBF, anyone who has been through it or been bitten by TBF will not have that same opinion.
By the time one calculates the cost of rebuilding their TBF'd engine/928, they are either married to it for life or are divorced with a bad taste in their mouths about the whole 928 automatic experience.
The more this information is circulated, the better it is for everyone who owns or wants a automatic 928!
05-28-2010, 07:06 AM
#40
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Releasing yearly is better than nothing but should not be used as permanent solution same way as custom clamp, factory shim setup or glue. Releasing few times and always finding preload should quickly lead to these other solutions. If not, owner better not complain about TBF which will definitelly happen.
TBF is one of those cases where some people simply refuse to believe faultless logic and eventually will cause themselves problems. They can't be helped and turned around no matter what evidence is shown to them. I have explainded it to few people over the years. Some still test their luck no matter what.
TBF is one of those cases where some people simply refuse to believe faultless logic and eventually will cause themselves problems. They can't be helped and turned around no matter what evidence is shown to them. I have explainded it to few people over the years. Some still test their luck no matter what.
05-28-2010, 08:51 AM
#41
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Hi Erkka,
Agreed with your statements except for using "glue" to stop this movement. It's a bad idea and gives owners more problems in the long run. It should not be viewed as an acceptable solution.
Kind regards,
Agreed with your statements except for using "glue" to stop this movement. It's a bad idea and gives owners more problems in the long run. It should not be viewed as an acceptable solution.
Kind regards,
05-28-2010, 02:33 PM
#42
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Its not best possible idea but it works until TT needs to com down. I would do it but to many its only cheap option as its at limit of their DIY capabilities if PKClamp is not counted.
05-30-2010, 10:12 PM
#43
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Constantine.....Does your 928 Super clamp allow the driveshaft free axial (sliding) movement of the driveshaft with respect to the driveplate/flywheel/crank?
If it does, it seems a logical and excellent solution, assuming it is well lubricated for wear.
Also, several people have asked if i bought the car knowing it had TBF failure. The answer is no, but i knew the car had lost oil, and had an engine failure, which i was told was a damaged crankshaft, but not specifically a thrust bearing problem. I did not know how expensive parts were, or even if oversize bearings are an option. I was aware that a used engine can cost £3000 as an exchange item. I did not know how much fun it was to remove the wiring through the bulkhead, or was i was in for, in removing the flywheel housing bolts in the back of the engine!! Oh yes, and here in the UK it's a nightmare to find a engine shop that can machine the block properly. I am an engineer, and it is a shame my CNC mill is to small for this motor. I may make custom shells and or thrust bearings to fix it, if the bores and pistons are still ok from being tipped sideways!
If it does, it seems a logical and excellent solution, assuming it is well lubricated for wear.
Also, several people have asked if i bought the car knowing it had TBF failure. The answer is no, but i knew the car had lost oil, and had an engine failure, which i was told was a damaged crankshaft, but not specifically a thrust bearing problem. I did not know how expensive parts were, or even if oversize bearings are an option. I was aware that a used engine can cost £3000 as an exchange item. I did not know how much fun it was to remove the wiring through the bulkhead, or was i was in for, in removing the flywheel housing bolts in the back of the engine!! Oh yes, and here in the UK it's a nightmare to find a engine shop that can machine the block properly. I am an engineer, and it is a shame my CNC mill is to small for this motor. I may make custom shells and or thrust bearings to fix it, if the bores and pistons are still ok from being tipped sideways!
05-31-2010, 02:58 AM
#44
Imo000,
Thanks for the update, very interesting.
I have had bearing failures in larger engines and cracks around the bearing pockets and these were repaired by "metalock". This is a drilling, tapping and metal stiching process across the crack.
It will depend on the failure and the consequences as to weather the block is salvagable.
Thanks for the details, an I hope I never have to worry about it. No movement in my flexplate in nearly 4 year or so "Locltite"
Tails 1990 928S4 Auto
Thanks for the update, very interesting.
I have had bearing failures in larger engines and cracks around the bearing pockets and these were repaired by "metalock". This is a drilling, tapping and metal stiching process across the crack.
It will depend on the failure and the consequences as to weather the block is salvagable.
Thanks for the details, an I hope I never have to worry about it. No movement in my flexplate in nearly 4 year or so "Locltite"
Tails 1990 928S4 Auto
05-31-2010, 08:19 AM
#45
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Constantine.....Does your 928 Super clamp allow the driveshaft free axial (sliding) movement of the driveshaft with respect to the driveplate/flywheel/crank?
If it does, it seems a logical and excellent solution, assuming it is well lubricated for wear.
Also, several people have asked if i bought the car knowing it had TBF failure. The answer is no, but i knew the car had lost oil, and had an engine failure, which i was told was a damaged crankshaft, but not specifically a thrust bearing problem. I did not know how expensive parts were, or even if oversize bearings are an option. I was aware that a used engine can cost £3000 as an exchange item. I did not know how much fun it was to remove the wiring through the bulkhead, or was i was in for, in removing the flywheel housing bolts in the back of the engine!! Oh yes, and here in the UK it's a nightmare to find a engine shop that can machine the block properly. I am an engineer, and it is a shame my CNC mill is to small for this motor. I may make custom shells and or thrust bearings to fix it, if the bores and pistons are still ok from being tipped sideways!
If it does, it seems a logical and excellent solution, assuming it is well lubricated for wear.
Also, several people have asked if i bought the car knowing it had TBF failure. The answer is no, but i knew the car had lost oil, and had an engine failure, which i was told was a damaged crankshaft, but not specifically a thrust bearing problem. I did not know how expensive parts were, or even if oversize bearings are an option. I was aware that a used engine can cost £3000 as an exchange item. I did not know how much fun it was to remove the wiring through the bulkhead, or was i was in for, in removing the flywheel housing bolts in the back of the engine!! Oh yes, and here in the UK it's a nightmare to find a engine shop that can machine the block properly. I am an engineer, and it is a shame my CNC mill is to small for this motor. I may make custom shells and or thrust bearings to fix it, if the bores and pistons are still ok from being tipped sideways!
To make this a sliding coupler connection would be much more costly than our Super Clamp, it would require the drive shaft to be made of a different material or at least treated differently to handle this type of wear and the coupler system would be a bit more involved than what is initially thought.
We did try a sliding coupler system initially but it did not work since the vibrations caused the coupler to rattle within itself since the drive shaft would have to be pinned to the back of the crankshaft as are the 5 speed drive lines.
Good luck with your engine build!
Last edited by Black Sea RD; 05-31-2010 at 02:59 PM.