Hi all, got a problem I have never come across before. I did some searching of the forms and found a bit of info, but not exactly what I was looking for.

I have a 87 IROC that I swapped a 1974 350 block into, stroked to 383. I wanted to do internal balance, but the machine shop couldn't get the crank balanced neutral so they made a plate to bolt to the back side of the fly wheel (T5 transmission).

Everything seemed fine at the initial startup and the motor broke in with no issues. After about 1500 miles, the throw out bearing went bad. The alignment of the tranny was good and I couldn't identify any other problems so I assumed that I got a bad bearing and replaced it.

Fast forward to 5000 miles, I am putting in a WC T5, different headers, and new motor mounts (should have replaced the motor mounts at the initial build but didn't). When I dropped the transmission, I found to my disgust that the throw out bearing was ruined again. The pilot bearing is fine and again nothing else seems wrong. So now I think that I must not have the transmission aligned correctly and make a note to check that again. The motor mount and header swap goes fine and I am putting some things back together at the front of the motor. When I start to tighten the bolts on the lower pulley, I am horrified to see the crank slide back about 0.2 inches (the tranny is still off).

I can pull the crank back and forth by ~ 0.2 inches. I have never seen this kind of end play happen before. I didn't have any indications of a problem with the motor, no strange sounds, no oil pressure issues, the motor was actually running really well.

From what I have read in the forms, this could be due to bad assembly (the lower end was put together by TPIS), or high clutch pressure. I am hoping that TPIS knows what they are doing and since I installed the clutch (Ram powergrip), maybe I did something wrong. I have done clutches before but never in this year with a hydraulic actuator. I thought that the clutch was self adjusting, what could have been done wrong with the clutch installation to cause this?

So this really sucks because I suppose this means the crank is dead, but should I not even start the engine again? I would like to get the heat cycles into the headers (ceramic coated) before tearing it all apart again. It seems really weird that there were no indications of a problem with this much end play.

Sorry for such a long winded post, but I wanted to include as much info as I could. Any ideas?

 

Bad thrust bearing/crank thrust surface. You'll need to pull that crank out and have it turned with new bearings. I had a similar problem with the 327 in my '68, I had .043 end play and that was bad enough to make the clutch chatter. You should have .005 max. I don't think it would hurt anything more by running it unloaded for a while.

 

Bad thrust bearing/crank thrust surface. You'll need to pull that crank out and have it turned with new bearings. I had a similar problem with the 327 in my '68, I had .043 play end play and that was bad enough to make the clutch chatter. You should have .005 max.

 

So would you say that the throw out bearing also going bad is a symptom of the thrust bearing going bad, or could transmission alignment or clutch installation be contributing to both problems?

Thanks

 

Usually early TO bearing failure is due to the the clutch not fully releasing so the bearing is spinning all the time.

 

So with this clutch setup how would I verify whether the clutch is fully releasing? As far as I can tell there aren't any adjusments.

Thank you for the help.

 

You kinda have to go by feel. ie, how far the pedal moves before it hits resistance. I don't recall there being any adjustment either. The master or slave could be bad, or maybe you just got a crappy Chinese made bearing that failed. Not uncommon these days.

 

So the motor came out this last weekend and was taken apart tonight. It looks like the bearing actually machined the crank, so that's pretty cool. I'll take it to TPIS and see what they say, I have a feeling they won't be able to do anything for me but this seems like an assembly issue to me. I've never seen this happen before.





Can anyone tell based on the info in the initial post and these photos if it was related to the assembly? Should I push them if they say there's nothing they can do?

Thanks

 

The bearing should be soft compared to the crank. I doubt it's an assembly problem.

 

That's a new one on me. I've seen cranks (Scat? I don't remember) with poor surface finish on the thrust face that eats its way through the bearing, but I've never seen a bearing eat through the crank.

 

Interesting, this was a Scat crank. The bearing is definately worn away on that side also, but the crank lost this battle.

 

I'm with Apeiron- the bearing should have lost that battle. The crank will get chewed up too, but usually the bearing is worn right down to the steel shell before that happens as bad as yours looks.

Still, something is apparently pushing forward on your crank with considerable force, causing it to eat up the thrust surface. It doesn't take a lot of force, either. The thrust bearing area can't take anywhere near as much load as, say, the mains or rod bearings. They don't get near as much oil and they are fully open on one side- the side that centrifugal forces are trying to throw oil off the bearing. When I say it doesn't take much load I mean like only 100 lbs. of force or so, applied constantly, will dramatically shorten their life.

So, you heard it here first- I think your dead TO bearings and your chewed up thrust surfaces are related somehow. Possibly becuase the clutch is not releasing fully when you let it out. That right there might explain both problems.

 

This failure could easily have been an assembly issue. In assembly I mean not only installation, but also tolerances. Was the crank thrust surface smooth, and what was the runout on it? What was the crank end play, and was the rear main properly seated? Was the rear main modified to provide additional oil to the rear thrust surface?

A Centerforce clutch requires about 500 pounds of pressure to dis-engage it. A RAM 3,000 lb diaphragm clutch requires a whole lot more. This pressure is placed directly onto the rear main thrust surface. Lot of cars running both of these clutches without rear main issues.

RBob.