28 vs 25mm shafts
02-21-2020, 05:54 AM
#16
Burning Brakes
Thread Starter
As Greg says.
shims can also be added / deleted and the circlip installed and removed with the shaft and engine both in situ. In this case the required at rest rear thrust (is it 0.3mm by memory?) can be set by ensuring that, with the shims and circlip in place, rear bolt tightened (so shaft is in correct fore / aft position) and with front clamp tight and holding flex plate hard up as forward as possible against shim arrangement and with flexplate UNBOLTED from flywheel, that there is the required rear thrust clearance between flex blare bolt position and flywheel - feeler gauges can be used for this. Thus when flex plate is then bolted to flywheel the required rearward thrust us exerted on the crank thrust bearing as per spec - to yield the same outcome as per Greg’s comment above.
not sure now in retrospect why we adopted the above method foe one car we did - maybe because it was altogether more simple - much like adjusting tappets with feeler gauges (no maths required or opportunity for bearing destroying mathematical errors).
shims can also be added / deleted and the circlip installed and removed with the shaft and engine both in situ. In this case the required at rest rear thrust (is it 0.3mm by memory?) can be set by ensuring that, with the shims and circlip in place, rear bolt tightened (so shaft is in correct fore / aft position) and with front clamp tight and holding flex plate hard up as forward as possible against shim arrangement and with flexplate UNBOLTED from flywheel, that there is the required rear thrust clearance between flex blare bolt position and flywheel - feeler gauges can be used for this. Thus when flex plate is then bolted to flywheel the required rearward thrust us exerted on the crank thrust bearing as per spec - to yield the same outcome as per Greg’s comment above.
not sure now in retrospect why we adopted the above method foe one car we did - maybe because it was altogether more simple - much like adjusting tappets with feeler gauges (no maths required or opportunity for bearing destroying mathematical errors).
02-21-2020, 10:24 AM
#17
The circlip, bearing and shims was a design initially used by Porsche and then abandoned. Why, no one really knows.
The Ritech clamp is one you should consider since it is much easier to put on and adjust to stop this drive shaft migration. It can also be removed if needed very easily for other maintenance.
I understand you doubt the need for anything more than just releasing the front flex plate pressure periodically. However just imagine if you have to get one of your 928 engine's rebuilt if TBF does happen.
The Ritech clamp is extremely cheap insurance in comparison.
The Ritech clamp is one you should consider since it is much easier to put on and adjust to stop this drive shaft migration. It can also be removed if needed very easily for other maintenance.
I understand you doubt the need for anything more than just releasing the front flex plate pressure periodically. However just imagine if you have to get one of your 928 engine's rebuilt if TBF does happen.
The Ritech clamp is extremely cheap insurance in comparison.
02-21-2020, 10:45 AM
#18
Rennlist Member
There never is an issue until there is and then it is too late. You may be lucky- you may not but why chance it?
TBF is not one of those things one "feels" is about to happen- it happens and invariably the first the owner knows about it is when the motor is seized the next time a start is attempted following the event. Someone with your awareness may just feel something is not right but...? Further, the mileage your GTS has covered is right in the "drop zone" for when it seems to happen on the examples we typically see [apologies- not trying to put the ******* up you].
For those who do not want to disassemble things there is the Ritech clamp. If you have yours out it really is a no brainer- Constantine's clamp. Not sure what the latest pricing is but last I heard they were very reasonably priced. Just leaving it to chance is Russian Roulette 928 style. Is it really worth risking a GTS motor?
02-21-2020, 12:58 PM
#19
Former Vendor
Once you attempt to install some shims, the washer, and the circlip on a 4 speed flywheel (in situ), measure everything up, remove everything to install the correct shims, and then re-assemble it again, you will understand.
While it's not impossible, it's a terribly "fumbly" job that can take hours...just "chasing" the pieces you drop, trying to get them onto the end of the shaft.
What might have been helpful, was a custom Porsche tool of a set of circlip players, about a foot long, with 3-4 bends along the way.
I sincerely doubt that this was possible, on any sort of an "assembly line". The guy doing this would be standing in a "sea" of dropped pieces, with other assembly workers yelling at him, all day long.
02-21-2020, 04:13 PM
#20
Yes. Agree. In an assembly line the Porsche advised method is the only sensible method.
one off - doing it oneself (ie at no labour cost) the in situ method was surprisingly easy.
not trying to advocate the in situ method - just saying it can be done quite easily - if needs / wants be.
one off - doing it oneself (ie at no labour cost) the in situ method was surprisingly easy.
not trying to advocate the in situ method - just saying it can be done quite easily - if needs / wants be.
02-21-2020, 04:42 PM
#21
Former Vendor
Yes. Agree. In an assembly line the Porsche advised method is the only sensible method.
one off - doing it oneself (ie at no labour cost) the in situ method was surprisingly easy.
not trying to advocate the in situ method - just saying it can be done quite easily - if needs / wants be.
one off - doing it oneself (ie at no labour cost) the in situ method was surprisingly easy.
not trying to advocate the in situ method - just saying it can be done quite easily - if needs / wants be.
My hands are too old, too fat, too big to get in there!
02-22-2020, 06:42 AM
#22
Burning Brakes
Thread Starter
02-22-2020, 06:47 AM
#23
Burning Brakes
Thread Starter
There never is an issue until there is and then it is too late. You may be lucky- you may not but why chance it?
TBF is not one of those things one "feels" is about to happen- it happens and invariably the first the owner knows about it is when the motor is seized the next time a start is attempted following the event. Someone with your awareness may just feel something is not right but...? Further, the mileage your GTS has covered is right in the "drop zone" for when it seems to happen on the examples we typically see [apologies- not trying to put the ******* up you].
For those who do not want to disassemble things there is the Ritech clamp. If you have yours out it really is a no brainer- Constantine's clamp. Not sure what the latest pricing is but last I heard they were very reasonably priced. Just leaving it to chance is Russian Roulette 928 style. Is it really worth risking a GTS motor?
TBF is not one of those things one "feels" is about to happen- it happens and invariably the first the owner knows about it is when the motor is seized the next time a start is attempted following the event. Someone with your awareness may just feel something is not right but...? Further, the mileage your GTS has covered is right in the "drop zone" for when it seems to happen on the examples we typically see [apologies- not trying to put the ******* up you].
For those who do not want to disassemble things there is the Ritech clamp. If you have yours out it really is a no brainer- Constantine's clamp. Not sure what the latest pricing is but last I heard they were very reasonably priced. Just leaving it to chance is Russian Roulette 928 style. Is it really worth risking a GTS motor?
But, then again, Im one of those who also think the original cam belt tensioner works perfectly fine when set up correctly. Never had an issue. :-)
02-22-2020, 08:31 AM
#24
Rennlist Member
Thanks for your input. I’ve been wrenching on these 928’s for some time. I’ve released quite a few flex plates and measured the end float on a lot of them. When setting this up per factory specs and releasing the flex plate at the the yearly oil change I have seen no issues. No visible movement on the flexplate when releasing.
But, then again, Im one of those who also think the original cam belt tensioner works perfectly fine when set up correctly. Never had an issue. :-)
But, then again, Im one of those who also think the original cam belt tensioner works perfectly fine when set up correctly. Never had an issue. :-)
02-22-2020, 09:38 AM
#25
Team Owner
FWIW before releasing the front pinch bolt see if the flywheel is free from forwards thrust,
gently pry the flywheel to the front of the car,
then pry rearwards,
if you hear the dull thunk and the flywheel doesn't spring forwards again,
then the thrust bearing is not preloaded
gently pry the flywheel to the front of the car,
then pry rearwards,
if you hear the dull thunk and the flywheel doesn't spring forwards again,
then the thrust bearing is not preloaded
02-22-2020, 03:30 PM
#26
Burning Brakes
Thread Starter
FWIW before releasing the front pinch bolt see if the flywheel is free from forwards thrust,
gently pry the flywheel to the front of the car,
then pry rearwards,
if you hear the dull thunk and the flywheel doesn't spring forwards again,
then the thrust bearing is not preloaded
gently pry the flywheel to the front of the car,
then pry rearwards,
if you hear the dull thunk and the flywheel doesn't spring forwards again,
then the thrust bearing is not preloaded