So you bought an EJ257 block to build on the side. The seller says it’s “good” and “was running.” I mean, they can say anything, right? That is until you pull the engine block apart and the crank suffered major rod bearing damage from either oil starvation or debris from other failing components.
Here we go to look at the bore housings of the main bearings on the engine block. They look perfectly round to the eye but only measuring tools will reveal how oval they really are. Heat isn’t your friend and is the major cause in warping the bore housings. Rod bearing failure will cause excessive heat if driven on. Even brand new blocks from Subaru can be out of round.
The pictures show the honing marks after a pass on the honing machine. You can see where the color is more dull and has minimal light reflection. There was no contact there with the honing stones. You can see the dark defining line, which was where the bearing sat. Half of the bore housing number 3 (middle) didn’t make contact while honing as with bore housing number 4, which did not make any contact except where the block halves met.
What do we do now? The issue here is you’ll have bearing clearances that are too small or too large. This will cause oiling issues to areas where they most need it. Also the warped mains will not be straight. This can cause bearing to crank journal contact. So when looking at a block to buy, ask about the block’s history. If the seller has the block apart, look for yourself before purchasing. An experienced machine shop that has an align hone machine will be able to straighten the bearing housings as long as they aren’t too out of round.