Originally Posted by fishspeed

Knife-edging is a process that a machine shop will do to a crank that will basically remove a lot of material from the crank counterweights, which are the large cast portions of the crank that connect the main bearing journals to the rod bearing journals. The machinist will remove the material at an angle and the result looks similar to a knife's edge, hence the term. The overall result is the crank has less weight, so it will spin faster easier (but also lose revs faster) and the 'knife-edge' will also cut through the air and oil easier, in effect reducing the parasitic drag from these variables.