Frank, on this forum and others common sense may be in very short supply with some posters. Anyone claiming today's machining process is cleaner than years ago is clueless, with plexiglass guards and wash tanks it may be cleaner for the operator and the working environment (which may help prevent metal trash getting into the engine when assembled) but the fact remains machining metal is a very dirty business.
The metal parts are still going to have very small machining marks that need to be mated as the engine runs regardless of how precise the initial fit is, the microinch surface rating is not going to be the optimal for a surface finish in mass produced engines due to the higher cost and machining time restraints, it may be a little finer than the old days but far from optimal.
The metal parts are still going to have very small machining marks that need to be mated as the engine runs regardless of how precise the initial fit is, the microinch surface rating is not going to be the optimal for a surface finish in mass produced engines due to the higher cost and machining time restraints, it may be a little finer than the old days but far from optimal.