Harley Davidson military motorcycle model 42 WLA-solo (civilian models WL & G 1940-1952). Operation and maintenance manual — page 3

Testing Valve Seating

If valve seats and valve faces have been smoothly and accurately refaced with grinders available for this purpose, very little grinding or lapping will be required to complete seating operation. Apply a light coat of fine compound to valve face, insert it in cylinder and give it a few oscillations with a screwdriver—just enough to give face and seat a lapped finish. Remove valve, wash valve face and seat thoroughly with clean gasoline and allow to dry, or dry with compressed air. If inspection shows an unbroken lapped finish around both valve face and seat, valve is well seated. If lapped finish is not complete around either valve or seat, further seating is required.