Thurst bearing failure?
 

Purchased the 928 with a problem of turning over slowly and sounds tight.



Difficulty turning over on starter motor

I have fitted new bosch starter motor, new battery and leads,

So the engine down and found marks on mains bearing and thrust bearings, what your opinion?

https://cimg6.ibsrv.net/gimg/rennlis...05a0323b13.jpg
https://cimg7.ibsrv.net/gimg/rennlis...91c3a8566c.jpg
https://cimg8.ibsrv.net/gimg/rennlis...57ae5ae3c9.jpg
https://cimg9.ibsrv.net/gimg/rennlis...e4203aae0e.jpg

Could you provide more information about the 928 in question like model, year, miles on the motor, etc.

Based on the report it sounds like you should have performed a crank end play check before you pulled and disassembled the engine
if your thrust bearing has the worst wear on the face pictured it still looks ok
otherwise the marks on the bearing web in the engine are also normal looking machining marks

But we also need more info year trans type miles

Thanks for reply never thought about end play it;s an auto how can you check the float / end play if i rebuild the crank back up it was tight to turn over by hand with wrench on crank end should i be able to turn by hand gripping the end of crank by hand no wrench ? .what shoul the end play / float be , engine supposedly rebuilt by the guy i bought from some 4/5 k

Not sure which way round your thrust baring photo was taken from but I would say you have not experienced thrust bearing failure in the catastrophic context we expect to see albeit you may have some excessive wear.

From the thrust bearing photo it seems you have [premature?] wear on one of the thrust faces and it would have been useful to know what the crank end float was before you stripped the motor. In the case of TBF it is the rear thrust face that gets hammered. fortunately no signs of the thrust bearing seizing or spinning.

What condition was the 2/6 big end bearing in?

Should be interesting to see how this thread opens up- we usually get questions before actions are taken. Is it my eyesight or did I spot copper showing through on a main journal or two?

End float should be in the region of 0.15mm to 0.2mm on a healthy motor.

It usually takes a 22mm long socket and a decent crank moment to turn the motor- I usually crank mine with my old torque wrench wound tight in more for the lever arm. Have never checked the actual torque needed to crank the motor but you are not going to do that with a short stubby 1/2 inch drive ratchet unless you have forearms like King Kong.

What other clues did you find that suggested an engine dismantle was required?
Who was the mechanic that rebuilt the engine?
How long was it running before the engine began to be hard to turn?

IIRC the thrust bearing must be set prior to torquing the girdle,
read the WSM for the particulars .

What other particulars did you find on taking it apart?
Did you turn the engine with the flex plate disconnected?

From the looks of things you did not need to split the block,
as nothing shows abnormal wear from what I see.
Were the cams hard to turn?

most end play checks I see show between .007 in and .010 in.
max is .016 in.

https://rennlist.com/forums/928-foru...crank+end+play

Cylinder walls don’t look right.

Ahh good point Dave,
they appear to have been honed,
but also appear to have been sleeved
OP says the engine was rebuilt so maybe the bores are whats causing the friction

Yup.

Yup.

If the walls have been honed and/or sleeved then all bets are off since we know that anything other than Alusil, Porsche rings and Mahle (not Mahle Motorsport) pistons is an experiment.

I could have measured crank turning torque on two GT long blocks (one with 100% new bearings, rings, pistons etc. all-through and the other not) I have on stands right now. But, since the OP has crossed the Rubicon at Warp 9 and has the crank on the bench I've got nothing.

But, the crank bearing surfaces look fine-enough to me.

Well, the thrust bearing doesn't look great. But, without knowing anything at all except that the motor was rebuilt, it's kind of hard to point fingers. If that's a "2-hour" bearing then yeah there's a problem. If automatic then one would naturally assume ridiculous preload from the TT shaft. Wear does appear to be on the trailing thrust surface.

The OP probably saved himself a lot of grief ($$,$$$) by doing this instead of guessing what might be wrong with the engine, meanwhile dumping money into it only to have a catastrophic failure from either a TBF incident or a blown motor from a prior poor rebuild.

At least now he can examine the engine in detail and plot a course of action for a proper rebuild.

It would be interesting to know the back story on this 928.

I concluded the same thoughts. I saw what appeared to be some copper looking breakthrough on one of the non thrust bearing mains. Even the pic of the thrust bearing seemed to indicate signs of light "scotch bright" marks not to mention some of the other astute observations.

I don’t see any copper. Where do you see copper?

On the first post first picture there is what seems to me to be a strange wear pattern. In the middle of the seemingly advanced wear pattern there is what to me looks like a shade of copper breaking through. Whether it is the lighting or strange reflection of optical effect I do not know but it caught my eye as did the wear pattern and it is not the thrust bearing journal either.

https://cimg0.ibsrv.net/gimg/rennlis...07a575b825.jpg