Boring and honing isn't just about punching out the cylinder bores to a larger size. You have to make sure each cylinder is perfectly round and straight (perpendicular to the centerline of the crank). When boring the block, the machinist should use a fixture that locates the block on the crank saddles and another that locates the proper place for each cylinder (commonly a B-H-J Bor-Tru plate). This can help fix cylinder bore misalignment from the factory. Typically, the bores will be bored within approximately 0.005 or 0.006 inch of the final diameter.

Boring is the process of cutting away metal with a carbide cutting tool. Honing is much the same except a stone is used and you deal with much smaller increments.

The last bit of material is left on purpose to be removed by the honing process. Honing a bore, when properly done, leaves a fine crosshatch of valleys in which oil collects. A perfectly smooth cylinder wall wears rings very quickly. For racing, make sure your machinist attaches a torque plate before honing. A torque plate simulates the stretch caused by torquing a cylinder head in place. Also, you must use a head gasket between the block and torque plate to properly simulate the stress caused by a cylinder head. The head gasket should be the same type used on the final build. Guild says he has seen variances caused by honing with a standard composition head gasket and then building the engine with an MLS (multilayer steel) gasket. Usually, honing is done with a series of progressively finer stones (usually three) and takes some time. That's why the boring and honing process on the cylinders can cost an average of $300 if not more.

On a rebuild, if the engine has not been damaged, you can often get by with a light re-hone that removes as little as 0.0005 inch. This is enough to etch the cylinder walls, but removes so little that you don't have to increase the size of the piston.