Why does the factory make oversized pistons? Are they for factory race engines?

 

say you blow your motor. either by bad rings, or throw a rod/break rods which may gouge the walls of the cylinders. you shouldnt put the same size pistons in there. even in a basic rebuild. alot of shops dont hone and bore and just stick stock bore pistons in there. it will hold but how accurate can it be. best bet is to bore and hone it out a bit bigger, the same size as the oversized pistons, to get the best seal possible.
cylinder walls may warp or get worn out in some ways after so many miles of driving.

 

That's the reason you hone. So, yeah.