thrust bearing damage

[mylittlecj5]

what would cause a thrust bearing to wear on one face?
its been a while since ive rebuilt an engine, and this is my first Amc.
when i tore this one down over the weekend, i saw the crank had a lot of endplay. then i found metal slivers in the oil pickup screen. when i removed the number 3 main cap, the thrust bearing was visibly worn on the forward side, lower bearing half.
the others are worn, but not nearly as bad as this one.
What would cause this condition? driving habits, oiling problems, ect?
engine is a Amc 360 out of a late 80's wagoneer DD/off road truck.

 

[Cheepjeep85]

did it have a real stiff aftermarket clutch? driver abuse, poor maintenance, could be caused by a number of things.

 

[mylittlecj5]

I don't have any history on this other than it was a daily driver turned trails truck that got rolled. I picked up the engine about a year ago and its been sitting since.

 

[Cheepjeep85]

if i had my guess i would say it was run pretty hard, do you know if it had a manual tranny behind it.

 

[mylittlecj5]

No it had a auto, cause I had to buy a (really pretty, shiny) flywheel from member Derf when I decided to get it running...

I did see that the engine has been professionally rebuilt in the mid/late 90's. All the bearings are stamped with 12/94.
Other than the thrust bearing and a little carbon under the intake, the engine is in pretty good shape. Should be a easy rebuild.

 

[Old Dog]

This is just a shot in the dark, but if the crank has been ground they could have made the jurnals to wide, this would let the crank have more end play than it should.

 

[Cheepjeep85]

This is just a shot in the dark, but if the crank has been ground they could have made the jurnals to wide, this would let the crank have more end play than it should.

ah possible too. are the bearings stamped with an undersize?

 

[mylittlecj5]

the rods and mains are both .010 under, but I don't see why they would widen the journals any?

 

[mylittlecj5]

this was a crude attempt at measuring the endplay before I tore it apart. LOL, not extremely accurate, but it shows the idea.

 

[Old Dog]

the rods and mains are both .010 under, but I don't see why they would widen the journals any?

All you need is a crank grinder having a bad day. It wouldn't take to much to get it started eating the bearing.
Somewhere you should be able to find the specs on how wide they should be. Maybe call a shop that grinds cranks.

Found it, it should have .003 to .008 end play.

 

[mylittlecj5]

Hmm, and I'm showing around .011. maybe its not as bad as I thought? still off, just not that much.

 

[Old Dog]

actually 3 thou. over the high is quite a bit.

 

[mylittlecj5]

Yea I was thinking it was about .250 out tho! LOL