TM 55-1 930-209-14&P-21
(4) Exhaust Valves
(a) An exhaust valve which is to be reused may be refaced, if necessary. To provide sufficient valve
strength and spring tension, edge of valve must not be less than 1/32 inch thick.
(b) Before either a new or used valve is installed, inspect valve seat in cylinder head for proper valve
seating. The proper angle for the seating face of the valve is 30°, valve seat insert should be 31 °.
(c) When a new valve seat insert is installed or an old insert is reconditioned, valve inserts must be
ground.
(d) Refer to Figure 6-17 for exhaust valve seat insert grinding specifications.
CAUTION
Do not allow grinding wheel to touch cylinder head when grinding inserts.
(e) Grinding will reduce thickness of valve seat insert and cause valve to recede into cylinder head. If,
after several grinding operations, valve recedes beyond limits shown in Figure 6-17, replace valve seat insert.
(f) After grinding has been completed, clean valve seat thoroughly with cleaning solvent and dry. Set a
dial indicator in position and rotate dial indicator to check concentricity of each valve seat relative to valve guide. If
runout is excessive, check for a bent valve guide before regrinding insert.
(g) After a valve seat insert runout is obtained that is within desired limits, determine position of
contact area between valve and valve seat insert. Apply a light coat of Prussian Blue, or similar paste to valve seat
insert. Next, lower stem of valve in valve guide and bounce, but do not rotate valve on insert. This procedure will
indicate area of contact on valve face. The most desirable area of contact is center of valve face.
(h) After valve seat inserts have been ground and checked, thoroughly clean cylinder head before
installing valves.
(i) Apply a light coat of engine oil on valve stems and install valves in cylinder head. If reconditioned
valves are used, install in same port from which they were removed.
(j) Hold valves in place with masking tape and turn cylinder head right side up on work bench. Place a
board under head to support valves.
6-36
