ARMY TM 9-2815-256-24 AIR FORCE TO 38G1-96-2 MARINE CORPS TM 2815-24/5 (1) Select a 0.  3125 inch (7.  9 mm) arbor that will extend approximately 2.  754 inches (6.  9 cm) above the valve seat.  Wipe the arbor stem with an oily cloth and insert into the valve stem guide. (2) Select a 30 degree angle, 1.  75 inch (4.  4 cm) grinding stone which is in good condition and install the stone in the hex drive. (3) Carefully lower the stone and hex drive unit on the arbor until the stone almost contacts the seat. NOTE Do  not  grind  too  long.    only  a  few  seconds  are  required  to  recondition  the  average  seat.    Avoid tendency to grind off too much.  Do not apply excessive pressure. (4) While holding the drive motor in line with the stone, grind the seat with a light tapping motion. (5) (5) Remove grinding unit and arbor from head. (6) Check valve recess, refer to paragraph 3-34.2. (7) Check valve seat width and contact pattern between seat and valve with blue bearing dye (HISPOTBLUE 107).  Maintain valve seat width within 0.059 to 0.079 inch (1.50 to 2.00 mm).  Use a vernier caliper or scale to measure seat width. CAUTION If valve seat width is too narrow, valve may burn or erode. (8) If necessary, reduce valve seat width by repeating steps (1) thru (5) using a 45 degree, 1.75 inch (4.4 cm) stone.  This reduces the width by increasing the smaller diameter of the valve seating area. (9) Remove arbor and recheck valve seat width, refer to step (7). n. Remove valve seat inserts as follows: CAUTION Be careful not to damage cylinder head when removing valve seats. (1) Valve seat inserts are made of sintered (powdered) metal.  To remove inserts: (a) Carefully heat insert(s) with an oxygen-acetylene torch at four opposite points until it becomes red hot. (b) Use a screwdriver or similar tool and carefully pry out insert(s) from bore. (2) After removal of inserts, thoroughly clean area around valve seat bore and inspect for damage or cracks. Replace cylinder head as necessary.  If valve with an oversize stem is to be used, an oversize valve seat insert must be installed. o. Measure valve seat bore in cylinder head as follows: (1) Compare dimensions of bore with valve seat insert.  Insert must have a press fit. (2) If bore dimensions are not within specification (or head has to be bored to accept a new insert when one was not previously used), machine head to specifications listed on FIGURE 3-122. 3-34.5. Assembly. a. Install valve inserts (10 and 11, FIGURE 3-119) as follows: 3-153