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![]() TM 5-4320-273-14
there is evidence of warping or deep pits. A good
valve spring seat locks (9) and valve stem cap (10).
method of detecting warping is to check each valve
(3) Release the valve spring compressor and
stem in a valve face grinder, and slowly rotate the
remove valve spring seat (11), valve spring (12), and
valve while the grinding wheel is brought near the
valve (3).
rotating valve face.
(4) Remove the valve tappets (14) from the crank-
(2) Using a valve face grinder, reface the valves
case. Do not remove valve guides (15) and valve seat
inserts (16) unless they are damaged.
to an angle of 45 degrees. Replace any valve that
measures less than 0.0625 inch (0.355 cm) from the
c. Cleaning and Inspection,
WARNING
top of head to the edge of the refaced outer circle.
(3) Install a pilot in the valve stem bore of the
DRY CLEANING SOLVENT, P-D-680
cylinder block. Set the stone on the valve reseating
or P-S 661, used to clean parts is
machine to the angle of 45 degrees and dress the
potentially dangerous to personnel
stone with the dresser. Place the grinder and stone
and property. Avoid repeated and
assembly over the pilot in the valve stem bore, and
prolonged skin contact. DO NOT use
grind inserts just enough to make a smooth seat.
near open flame or excessive heat.
(4) After grinding, valves and inserts should be
Flash point of solvent is 100 to 138F
lapped with a suitable lapping compound or they will
(38 to 60C).
leak due to improper seating within the first few
(1) Clean the top of the cylinder block with a
hours of operation.
scraper and cloth dampened in cleaning solvent (fed.
(5) Apply lapping compound to the valve face
spec. P-D-680), Clean all dirt and deposits from the
and put the valves back into their guides. Lap the
cooling fins with a scraper or putty knife.
valves by rotating them back and forth with a
(2) Clean all other parts with cleaning solvent;
reciprocating advancing tool.
dry thoroughly.
(6) Occasionally lift the valves and reseat them
(3) Inspect the cylinder block for cracks, scored
in a different position to ensure a uniform seat which
or scratched cylinder walls, or other damage. Replace
will show entirely around the valves, After valves
the block if damage cannot be corrected.
have been lapped in evenly, remove them from the
(4) Check the cylinder bores for wear. Measure
block and clean the valves and block.
the cylinder bores with an inside micrometer.
(7) When the grinding is completed, check the
Measure the bore lengthwise and crosswise above the
seat for concentricity, using a dial indicator.
ring travels; repeat the measurement at the top of
(8) With the valve stems inserted in the guide,
t h e cylinder bore. T h e difference in these
the stems shall have a clearance of 0.0025 to 0.0045
measurements will determine the amount of wear in
inch (0.006 to 0.011 cm). When the clearance becomes
the cylinder bore, the taper, and the out-of-round
0.008 inch (0.02 cm), you should replace the guides by
condition. If cylinder bores are worn more than 0.005
pressing them out with a driver that is slightly
inch (0.012 cm), rebore the cylinder with conventional
smaller than the external diameter of the guide. The
reboring equipment and hone until the bores are not
driver is also used to press in the new valve guides.
more than 0.001-inch (0.002-cm) out-of-round and are
not tapered more than 0.001 inch (0.002 cm). Nor-
e. Reassembly and Installation.
mally reboring to a 0.020-inch (0.05-cm) oversize is
(1) Install valve tappets (14, fig. 6-11) in the
sufficient. Maximum allowable oversize is 0.040 inch
engine block.
(0.1 cm).
(2) Place the valve springs (12) in their respective
(5) Clean the valves with a wire wheel brush to
valve chambers.
remove carbon from the valve faces and gum deposits
(3) Insert the valves (13) into the same bores from
from the stems. Wash the springs with cleaning
which they were removed. Assemble the valve stem
solvent (fed. spec. P-D-680); dry thoroughly.
cap (10) and valve spring seat (11) on the valve.
(6) Clean the valve seat insert and the top of the
(4) Using a valve spring compressor, compress
cylinder block. Inspect the valve-seat inserts for
the valve spring and install valve spring seat locks
looseness and excessive wear replace as necessary.
(9).
(7) Inspect the valve springs for breaks and wear.
(5) Position gasket (4) on crankcase and install
Compare with a new spring and replace if weak or
cylinder block assembly (3). Secure cylinder block
damaged.
assembly to crankcase with Lockwasher (2) and nut
(l).
(8) Inspect the valves for burned, pitted, or crack-
ed faces; replace if defective or if grinding is not
NOTE
plausible.
Tight.en cylinder block mounting nuts to 62 to 78 foot-
pounds (8.57 to 10.78 kg-m) torque.
d. Valve and Valve Seat Refacing.
(1) Replace valves and valve seats only when
(6) With the tappets in their lowest position on
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