what does undersized bearings mean??

[dusper4]

i am looking to rebuild my engine 4.0ohv and i was looking at bearing on ebay and they are like .020, .030 undersized. i was wondering what does this mean and do i have to get them all the same undersize or do i want actual size. this is my first engine rebuild and i wanted to do it myself so any help would be great.

 

[Rick]

If the crankshaft has been cut you need the undersized bearings to match the new dimensions of the crank journals. If the crank has never been machined you need standard bearings.