TM 10-3930-660-34 3-7. CYLINDER HEAD ASSEMBLY - REPLACE/REPAIR (Cont’d) b. Install exhaust valve service seats in the same manner described for the intake service seats, see STEPS 5b through 5j above. NOTE If it can not be accurately determined that service valve seats have been ground only once after initial installation, replace the seat. 7.   GRIND VALVE SERVICE SEAT(S).  GRIND SERVICE SEATS (15) FOR A FEW SECONDS ONLY TO AVOID MAKING THEM TOO WIDE. a. Valve seats marked with two X’s on the cylinder head have service seats installed.  Service seats, like the parent metal seats, can only be ground once after initial installation. b. Grind service seats in the same manner, and to the same tolerances, as used for grinding the integral seat in STEP 4 above. 3-47