Align HoneAs engines run, especially performance engines, the main caps can slip against its mating surfaces. This is called cap walk. After a while this surface can wear down, which decreases the main bearing oil clearance, to a point that the main bearing spins in the block. This why it is very important to check the main housing bore to make sure it is round and the correct size. Even if the bearings that came out look fine, when you retorque the caps on the block with new bearings you will loose some bearing clearance. This could put the clearance dangerously low. At Wells Racing Engines We will not assemble any engine until we have checked the housing bores!