valve lapping

[Bentwings]

Yes , you are correct . The surface of the valve and my seat are similar
But I'm talking about scratches....caused by machining

The lapping valve and seat can be fast or slow, just one time or many times depending on the surface of the valve and seat when machining - of course concentricity is necessary.
(concentricity between valve and seat on my engines: I don't know how precise it is but it can be called enough)
With me, most of the leaks between the valve and the seat (between the needle and the nozzles in a diesel engine) are from scratches or the like due to surface machining - Lapping is my best choice

Almost all of my valve machining was don on with valve grinding equipment valves were easily regroups or checked for concentricity just by chucking them in the grinder seats were done with seat grinder and variety of stone wheels there were various grits available. I turned a few valve in the lathe but not many . Most automotive valve finishing today is done with special cutters in a milling machine or dedicated machine lapping is a final finishing process just to get the very best seal . Valves go everywhere but straight when they get hot . Spring pressures are so high today it’s a wonder there are not more dropped valves .