This is a machining process in which the bore in which the crankshaft journals are trued. Typically they are bored .020", .040", .060" or .080" over the standard bore size. Most machine shops will stamp this number at the top of the case under where the oil cooler mounts. Whenever this is done, you will need to use bearings with an over-sized O.D. to ensure a proper fit.

A procedure used to re-align main bearing or camshaft bearing bores to bring them back into alignment after warping of the block or alignment shifts due to long-term mechanical stresses. By securing the block and then passing a single boring tool through all the bores without changing the alignment of the tool, the bores are restored to proper position. Properly aligned bores ensure that each bearing will carry equal load.