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Understood. Before there were valve grinding machine tools, valve seating was accomplished by lapping the valve face>valve seat surface. Perfectly adequate for the level of engine performance in thos vintage times. Even when valve facing machines were in use, there were old school mechanics that did it by lapping. Even today, many techs still rely on some level of lapping to ensure a tight seal. Things is, if overdone, the lapping process can create a lapping rut that causes the valve face and seat to be uneven (I.e. no longer a flat, machined surface).
Will the customer know the difference? Probably not, maybe a loss of compression 50k miles down the road. More demanding engine performance goals might result in some premature power loss or power not realized due to some level of combustion chamber leakage.
Can someone quantify the power difference between a leak down difference of 2% vs 4%?
Sherwood
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