928 Crank Thrust bearing, The Weakest Link
#1
Three Wheelin'
Thread Starter
Join Date: May 2001
Location: Hudson Valley NY
Posts: 1,641
Likes: 0
Received 0 Likes
on
0 Posts
928 Crank Thrust bearing, The Weakest Link
There have been many excellent threads on 928 engine rebuilding and modifications, by many talented Rennlist members, none of which have addressed what I think is the weakest link in a 928 engine, the crank thrust bearing.
Below are excerpts of a crank thrust bearing failure article.
http://www.aa1car.com/library/2003/eb50331.htm
“The crankshaft can be installed with standard bearings or oversize thrust bearings. But if oversized bearings are used, the crankshaft thrust surface must be remachined to compensate for the increased thickness of the bearing. If not, the crank may not have the proper amount of end play”.
“Overloading
AERA says a number of factors may contribute to wear and overloading of a thrust bearing:
• Poor crankshaft surface finish;
• Poor crank surface geometry;
• External overloading due to:
a) Excessive torque converter pressure;
b) Improper throw out bearing adjustment;
c) Riding the clutch pedal;
d) Excessive rearward crankshaft load pressure due to a malfunctioning front-mounted accessory drive.”
I often wondered if an over sized / heavy crank pulley in super charged engines would overload the thrust bearing.
Below are excerpts of a crank thrust bearing failure article.
http://www.aa1car.com/library/2003/eb50331.htm
“The crankshaft can be installed with standard bearings or oversize thrust bearings. But if oversized bearings are used, the crankshaft thrust surface must be remachined to compensate for the increased thickness of the bearing. If not, the crank may not have the proper amount of end play”.
“Overloading
AERA says a number of factors may contribute to wear and overloading of a thrust bearing:
• Poor crankshaft surface finish;
• Poor crank surface geometry;
• External overloading due to:
a) Excessive torque converter pressure;
b) Improper throw out bearing adjustment;
c) Riding the clutch pedal;
d) Excessive rearward crankshaft load pressure due to a malfunctioning front-mounted accessory drive.”
I often wondered if an over sized / heavy crank pulley in super charged engines would overload the thrust bearing.
#3
Three Wheelin'
Thread Starter
Join Date: May 2001
Location: Hudson Valley NY
Posts: 1,641
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Charley B
I wasn't aware there had been any incidence of 5spd TBF.
#4
Instructor
Join Date: Aug 2006
Location: New Berlin, WI
Posts: 232
Likes: 0
Received 0 Likes
on
0 Posts
According to Jaguar "hot rod" books, the well known old XKE 6 is subject to thrust bearing failure which is attributed to racing clutches with heavy PP's. The fear was the dreaded 'clutch change' which is a big deal on an XKE (can't be worse than a 951). Guys over did the clutch hoping to never replace it and ruined their thrust face. The big warning the Jag guys give is it is hard to get someone to grind the face good enough. This operation must be super duper and most hacks these days can't get it smooth enough or at 90 degrees to the axis.
#5
Steve,
Thanks for starting this thread, I didn't know you could modify the crank for oversize thrust bearings.
I'm in the middle of a motor build right now so this is perfect timing for me -- Thanks
P.S. can the MBZ 5spd auto be retrofitted to a late model S-4 trans axel ? Is there enough info on
that to start another thread, I definatly want to keep this thread moving full speed ahead... Yes there
are some really talented engine guys in this 928 community these days, but your the only really
knowledgeable trans guy -- thanks for looking after us.
Thanks for starting this thread, I didn't know you could modify the crank for oversize thrust bearings.
I'm in the middle of a motor build right now so this is perfect timing for me -- Thanks
P.S. can the MBZ 5spd auto be retrofitted to a late model S-4 trans axel ? Is there enough info on
that to start another thread, I definatly want to keep this thread moving full speed ahead... Yes there
are some really talented engine guys in this 928 community these days, but your the only really
knowledgeable trans guy -- thanks for looking after us.
#7
Race Director
Very interesting read......so lets see we have Timing belt failures, thrust bearing failures & 2-6 rod bearing failures (in track cars) to worry about......so for the ultimate in 928 worrying have an automatic track car!!!
Trending Topics
#9
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,572
Received 1,690 Likes
on
1,099 Posts
I'm having difficulty in visualizing TBF for a 5-speed 928 due to:
The t/o bearing isn't "adjustable." I suppose that it could be improperly installed, but I would think the clutch assembly would disintegrate before TBF.
The same goes for riding the pedal. Assuming that the clutch assembly is correctly installed, when you depress the clutch pedal the release arm levers towards the rear and releases the pressure on the disc. The intermediate shaft slides freely in the guide tube, is clamped to the shaft in the TT and cannot move relative to the flywheel?
How can either of the above conditions cause forward pressure on the crank (assuming a correctly installed clutch assembly)? I know you know a hell of a lot more about this than I do....
Originally Posted by Steve Cattaneo
b) Improper throw out bearing adjustment;
c) Riding the clutch pedal;
c) Riding the clutch pedal;
The same goes for riding the pedal. Assuming that the clutch assembly is correctly installed, when you depress the clutch pedal the release arm levers towards the rear and releases the pressure on the disc. The intermediate shaft slides freely in the guide tube, is clamped to the shaft in the TT and cannot move relative to the flywheel?
How can either of the above conditions cause forward pressure on the crank (assuming a correctly installed clutch assembly)? I know you know a hell of a lot more about this than I do....
#12
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,572
Received 1,690 Likes
on
1,099 Posts
Originally Posted by SharkSkin
Dave, the crank is pulled rearward, wearing the front thrust face of the bearing when riding the clutch.
Duh.
Some days I'm decidedly half-dimensional. I'm all concerned about forward pressure on the bearing and forget that it can move the other way too.
Ok. That 'splains riding the clutch pedal and monster-strong clutch.
How about 't/o bearing adjustment' Obi-wan?
#13
Three Wheelin'
Thread Starter
Join Date: May 2001
Location: Hudson Valley NY
Posts: 1,641
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Larry Velk
According to Jaguar "hot rod" books, the well known old XKE 6 is subject to thrust bearing failure which is attributed to racing clutches with heavy PP's. The fear was the dreaded 'clutch change' which is a big deal on an XKE (can't be worse than a 951). Guys over did the clutch hoping to never replace it and ruined their thrust face. The big warning the Jag guys give is it is hard to get someone to grind the face good enough. This operation must be super duper and most hacks these days can't get it smooth enough or at 90 degrees to the axis.
#14
Three Wheelin'
Thread Starter
Join Date: May 2001
Location: Hudson Valley NY
Posts: 1,641
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by 90 S-4
Steve,
Thanks for starting this thread, I didn't know you could modify the crank for oversize thrust bearings.
I'm in the middle of a motor build right now so this is perfect timing for me -- Thanks
P.S. can the MBZ 5spd auto be retrofitted to a late model S-4 trans axel ? Is there enough info on
that to start another thread, I definatly want to keep this thread moving full speed ahead... Yes there
are some really talented engine guys in this 928 community these days, but your the only really
knowledgeable trans guy -- thanks for looking after us.
Thanks for starting this thread, I didn't know you could modify the crank for oversize thrust bearings.
I'm in the middle of a motor build right now so this is perfect timing for me -- Thanks
P.S. can the MBZ 5spd auto be retrofitted to a late model S-4 trans axel ? Is there enough info on
that to start another thread, I definatly want to keep this thread moving full speed ahead... Yes there
are some really talented engine guys in this 928 community these days, but your the only really
knowledgeable trans guy -- thanks for looking after us.
#15
Three Wheelin'
Thread Starter
Join Date: May 2001
Location: Hudson Valley NY
Posts: 1,641
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Fabio421
Is there enough material there to retrofit with a roller bearing?