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TM 5-4210-220-34
2-19.
ENGINE - Continued
2-19.7
Exhaust Valves - Continued
(4) Check the dimensions of the counterbore. Diameter should be 1.440 1.441 in. (36.58 36.60 mm) and a
depth of 0.3395 0.3505 in. (8.623 8.903 mm). The counter bores should be concentric with the valve guide
within 0.002 in. (0.051 mm). If necessary use a valve seat insert which is 0.010 in. (0.25 mm) oversize on
the outer diameter.
(5) Immerse cylinder head for 30 minutes in a hot water both at 200 deg. F (93 deg. C).
(6) Rest the cylinder head, bottom side up, on a bench and place a new insert in the counter bore. Check valve
seat side is up.
(7) Quickly, to avoid the insert heating up, drive the insert in place with tool J24357, until it seats solidly in the
cylinder.
(8) Grind the valve and check for concentricity as detailed in d following.
d.
Exhaust Valve And Valve Seat Regrind
NOTE
An exhaust valve may be refaced if necessary. However, to provide sufficient strength and spring tension,
the edge of the valve at the valve head must not be less than 0.031 in. (0.78 mm) inch thickness after
refacing.
When a new valve seat insert is installed or an old insert is reconditioned, using grinding set J7040 with
adaptor set J24566.
Do not permit any grinding wheel to contact the cylinder head. If the wheel will contact the head, install a
new insert.
(1) Install a 31 deg. grinding wheel on the grinding tool and dress the valve seat insert.
(2) Open the throat of the insert with the 60 deg. grinding wheel.
(3) Grind the top surface of the insert with a 15 deg. grinding wheel to narrow the width of the seat.
(4) Adjust the center of the 31 deg. face with the 15 and 60 deg. grinding wheels as required.
(5) Clean the valve seat and ensure it is dry.
(6) Set dial indicator J8165-2 in position shown and rotate it to determine the concentricity of the valve seat insert
relative to the valve guide. If total runout is exceeded, check for a bent or worn valve guide before regrinding
the seat. Valve seat runout should be less than 0.0020 in. (0.051 mm).
(7) After completion of grinding, apply a thin coat of Prussian blue to the seat insert.
(8) Bounce the valve in the insert; do not rotate. Check the area of contact. If necessary reface the valve itself.
(9) Use valve refacing equipment, and grind valve face to 30 deg. Keep dimensions within tolerances shown.,
2-212
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