Do New Valves Need to Be Lapped?

New seats, with new valves should require no lapping to get a good seal - my machinist refuses to lap in the first place, considering it to be a half-baked solution.

Is lapping valves necessary?

Although some seats may need two or three times of lapping, it is not necessary or good to over-lap the valves. It is unlikely, but possible, to remove too much, and doing so will ruin the valve seat.

How long should you lap a valve?

The lapping process for each valve should take less than a minute if the valve seat and face were ground correctly.