i pulled the rear main bearing and found GMM400 and 001 stamped on it. how do i know if its -.001 or +.001 ? these are the orginal bearings and i was thinking of replacing them without tearing the crank out of it.

do you own a micrometer?

can you catch your fingernail on any of the bearing journals?

if you answered no to the first question and yes to the second, dont bother. just take it to a machine shop to have it turned.

i have a micrometer and there arent any scratches on the journals but i can see a little copper on the side of the lower bearings.

i pulled the rear main bearing and found GMM400 and 001 stamped on it. how do i know if its -.001 or +.001 ? these are the orginal bearings and i was thinking of replacing them without tearing the crank out of it.

I'm thinking they didn't add ten thou to the crank....Get some .0010 bearings and green plastigage....In my head I can't think of the assembly for the rear main but I'm prety sure if it's a one piece you won't want to take it apart from underneath. Better make sure before you do that.

its the older two piece rear main, would those be +.001 bearings your referring too? i havent done this since highschool auto mechanics.

its the older two piece rear main, would those be +.001 bearings your referring too? i havent done this since highschool auto mechanics.

I don't know that they're identified by a + or - as there's only one way they can go, the crank only gets smaller. Maybe a engine builder can chime in?

No it would be 10 under, you can only grind a crank down not add to it....if your just going to replace the bearing defiantly make sure you plastigage it.

Cant the bearing go bigger od too. As in if you align bore the journals. Probably not the case on an original block though.

when you buy oversized bearings, +.001, +.002, +.003 etc is added to the bearing.

thanks for the info guys, much appreciated