Is it an acceptable practice to mix one half of an undersized bearing (.001) with one half of a normal bearing to reduce bearing clerarance?

I have just a little too much clearance on most of my mains but think the full .001 might be too much.

 

dude, ive done that on old beaters to get down the road but,i wouldnt on a nice car, as its to much trouble to sling those engines in and out of these camaros, and usally when that happens you need a new crank, rod bearings etcetra also so usally i wind up goin with a crank kit and a new rod for whichever is loose or total rebuild.

 

It's OK to do that; as long as you put the same kind of bearing in all the same places. Like, all the block halves std, and all the cap halves .001" under. Otherwise you create the same effect as the block needing align-bored.

Still, that's hair-splitting. Like I told somebody else the other day, "measure with micrometer, mark with chalk, cut with axe".

Your clearance should be .0015" - .0025" for a street motor. I like to build mine on the tight side (both rods and mains), and use thin oil. If it's out of that range, but .001" under is too much, then polish the crank with 600 grit and then 1500 grit to size it. Use an old V type fan belt wrapped twice around a strip of sandpaper wrapped around the journal; lube it with ATF; and bolt the crank REAL SECURELY to something. I usually bolt them to my engine stand when I polish them. If you want to take off ALOT of metal FAST, start with 320 grit.

 

My machinist suggested doing exactly that, in order to get clearances bang on, if needed. I didn't, and I think I had .0025-.0027" clearances on the mains (plastigauge measurements, so who really knows what they were).

the belt, wrapped around the sand paper, wrapped around the crank? I'm getting lost in that picture you painted there, come again?
Wouldn't you want to use a serp belt, since it's a bit wider? Then say, wrap the paper around the journal I guess, tape it on, put some ATF on the paper, then put the belt over it, and somehow move the belt to keep some pressure on, moving it around to put the pressure on the crank at different angles, and keep the rotating the belt to move the paper around?

 

A serpentine belt is too wide, you wouldn't be able to put a full wrap on it. You want the belt to go fully around the journal once to put even pressure everywhere.

 

Well I ordered a set of .001 undersized bearings so they should be here in a few days. I'm going to put them in and see what my plastigauge comes out to and go from there; polishing the crank if need be.

 

I thought your crank was .010" under already, wouldn't you need .011" undersize bearings?
Maybe I'm thinking of someone else..

 

Nah my crank is still stock. Its been polished though