TM 9-4940-421-14
the cylinder block.
6-12. VALVES.
(2) Lightly coat the entire valve seat with a good
a General. The valves are lifted by tappets located
quality water-soluble, valve-grinding compound. Slip a
in the crankcase. The tappets are raised by the lobes on
light lifting spring over the valve stem, and lubricate
the camshaft. The firing order of the cylinders is
the stem. Drop the valve into its original place in the
1-3-4-2. Number 1 cylinder is the nearest one to the
cylinder block. The lifting spring should barely hold the
flywheel in the left bank of cylinders; number 3
valve face off its seat. Set the grinding tool on the valve
cylinder is the other one in this bank. Number 2
head, and press down until the valve is seated. Turn the
cylinder is the nearest one to the flywheel in the right
valve one-quarter turn, first in one direction, then the
bank of cylinders and number 4 is the other (fig 4-4).
other. Do this three or four times. Release pressure on
b. Removal
the valve so that the lifting spring will lift it from its
(1) Remove the governor (para 4-23).
seat, and turn the valve 10 degrees thru 15 degrees to
(2) Remove the cylinder heads (para 6-11).
another position. Repeat the grinding. Do this until all
(3) Remove the valve covers (fig 6-6).
NOTE
of the compound is rubbed off the valve seat. Take out
Tag or otherwise identify each valve and its parts so they
the valve, apply fresh compound, and repeat the grind-
will be reinstalled in the same guide and valve chamber
ing operation as necessary.
from which they were removed.
(3) Do not overgrind the valves. Occasionally clean
(4) Use a valve spring compressor and compress
the valve and its seat to see how the grinding is
the valve spring. Remove the pair of valve spring seat
progressing. When all of the pits and grooves have dis-
locks, the valve stem rotator, and valve spring seat.
appeared wipe the valve and its seat clean and place 3
Remove the spring compressor, lift out the valve, and
to 10 soft pencil marks on the valve seat. Drop the valve
remove the valve spring.
in place. Turn it one-quarter turn, and remove. A per-
c. Cleaning and Inspection.
fect seat will be identified if every pencil mark shows
(1) Clean the valves on a wire wheel brush to
where the valve has rubbed it. If any pencil marks re-
remove carbon from the valve face and gum deposits
main untouched, continue the grinding.
from the stems. Wash the springs with cleaning solvent
(4) When the grinding is completed, clean off all
and dry thoroughly (app D).
traces of the cleaning compound. Check the valve seat
(2) Clean out the valve guides in the cylinder block
for concentricity with a dial indicator.
and blow out with compressed air.
f. Valve Assembly Installation.
(3) Clean the valve seat inserts and top of the
(1) Place the valve springs (5, fig 6-6) in their
cylinder block.
respective valve chambers.
(4) Inspect the valves for burned, pitted or cracked
(2) Insert the valves (15) into the same bores from
faces. Replace a burned, cracked or deeply pitted valve.
which they were removed. Assemble the valve spring
(5) Inspect the valve springs for breaks and wear.
seats (4) on the valve stems. Compress the valve springs
Replace if weak or damaged.
and install the valve spring seat locks (3).
(6) Inspect the valve seat insert for looseness and
(3) Install the cylinder heads.
excessive wear.
g. Tappet Clearance Adjustment.
(7) Inspect and replace all unserviceable parts.
(1) Make sure the engine is cold.
d. Valve and Valve Seat Refacing.
(2) Crank the engine slowly until the no. 1 piston
(1) Reface valves and valve seats only when there
is rising in the compression stroke. Continue cranking
is evidence of warping or deep pits. A good method of
until the marked vane on the flywheel alines with the
detecting warping is to check each valve stem in a
no. 1 centerline mark on the flywheel shroud which is
valve face grinder, and slowly rotate the valve while
45 degrees counterclockwise from the vertical (fig 4-4).
the grinding wheel is brought near the rotating valve
(3) Adjust the valve tappet clearance as shown in
face.
(2) Using a valve face grinder, reface the valves to
0.016 inch. Adjust the inlet valve tappet clearance to
an angle of 45 degrees. Replace any valve that
0.008 inch.
measures less than 0.0625 inch from the top of head to
NOTE
the edge of the refaced outer circle.
Chalk mark the vane directly opposite the marked vanes on
(3) Install a pilot in the valve stem bore of the
the flywheel. To determine the 180 degree turn mentioned,
turn the crankshaft until the chalk-marked vane is alined
cylinder block. Set the stone on the valve reseating out-
with the no. 1 cylinder centerline.
fit to the angle of 45 degrees and dress the stone with
(4) Turn the engine crankshaft 180 degrees clock-
the dresser. Place the grinder and stone assembly over
wise and adjust tappet clearance on the no. 3 cylinder.
the pilot in the valve stem bore, and grind just enough
( 5 ) Turn the crankshaft clockwise until the
to make a smooth seat.
marked vane is alined with the no. 2 cylinder centerline
e. Valve Grinding Procedure.
which is 45 degrees clockwise from the vertical. This
(1) Remove all traces of carbon from the face of
