ARMY TM 9-2815-259-24 AIR FORCE TO 38G1-125-2 MARINE CORPS 09249A/09246A-24 5-114 CAUTION Support weight of grinder to avoid excessive pressure on grinding stone.   Failure to comply could result in damage to valve seat. CAUTION Do not grind valve seat too long.  Only a few seconds are required to recondition the average valve seat.  Avoid tendency to grind off too much.   Do not apply excessive pressure.  Failure to comply could result in damage to valve seat. 4 While applying light pressure, carefully grind valve seat with grinding stone. 5 Remove arbor, grinding stone, and pilot from valve seat. CAUTION If valve seat width is too narrow, valve may burn or erode.  Use care when narrowing valve seat width. 6 Check valve seat width with vernier caliper.  Valve seat width should be 0.059 - 0.079 in. (1.50 - 2.00 mm).  If valve seat is too wide, reduce width by repeating steps 1 through 5 using a 45° grinding stone. 7 Position new or refaced valve in cylinder head and check contact between valve seat and valve face using blue bearing dye.  If necessary, lap valve onto valve seat using a lapping tool and lapping compound.  Replace valves and valve inserts as necessary. 8 Check valve recess in cylinder head, refer to step 4.7.4.(b). NOTE It is not necessary to replace valve seat inserts if valve seats were successfully ground. (m) Replace valve seat inserts as follows: CAUTION Do not use oxygen-acetylene torch to remove valve seat inserts.  Oxygen- acetylene torch will alter the hardness of cylinder head and could cause damage to engine. 1 Raise a burr on bottom of valve seat insert. 2 Protect surface of cylinder head with cardboard or cloth.