TM 5-4320-218-15
four times. Release pressure on the
shows where the valve has rubbed it.
valve so that the lifting spring will
If any pencil marks remain untouched,
l i f t it from its seat, and turn the
continue the grinding.
valve 10 degrees through 15 degrees
(4) W h e n the grinding is completed.
t o another position. Repeat the
clean off all traces of the cleaning
g r i n d i n g . Do this until all of the
compound. Check the valve seat for
compound is rubbed off the valve
concentricity with a dial indicator.
seat. Take out the valve, apply fresh
g. Valve assembly installation.
compound, and repeat the grinding
(1) Place the valve springs (19, fig. 30)
operation as necessary.
in their respective valve chambers,
(3) Do not overgrind the valves. Occa-
(2) Insert the valves (9) into the same
sionally clean the valve and its seat
bores from which they were removed.
to see how the grinding is progress-
Assemble the valve spring seats (20)
ing. When all of the pits and grooves
on the valve stems. Compress the
have disappeared, wipe the valve and
valve springs, and install the vlave
its seat clean and place 3 to 10 soft
spring seat locks (24).
pencil marks on the valve seat. Drop
(3) Install the valve covers.
the valve in place. Turn it one-quar-
(4) Install the cylinder heads.
ter turn, and remove. A perfect seat
will be identified if every pencil mark
(5) Install the governor.
Section IX. VALVE-SEAT INSERT
Caution: Do not attempt to drive in an over-
103. Description
sized insert before machining the counterbore.
The valve seats are replaceable, hardened
inserts which are pressed into the cylinder
d. Finish the counterbores in the cylinder
blocks. The inserts should be replaced if they
blocks so that bore-to-insert interference is be-
are pitted or burnt to the point where ordi-
tween 0.001 and 0,003 inch. Chill the inserts
nary grinding procedures will not make them
with dry ice; then, using a pilot driver, tap the
serviceable.
insert in place with light blows. Peen the
insert to anchor it in place.
104. Valve-Seat Insert Replacement
e. Reface each insert if necessary to make
a. Remove, clean, and examine the valves as
their valve seats concentric with the valve-stem
instructed in paragraph 102.
b o r e , Use a dial indicator and make sure
b. Using a suitable puller, remove the ex-
that the valve seats are concentric. Regrind
haust valve-seat inserts, Take care not to dam-
the valve seats if necessary.
age the insert counterbore.
f. Install the valves, and adjust the tappet-
c. Clean all the carbon from the insert coun-
terbore, and from the valve port.
clearance as instructed in paragraph 102.
Section X. TIMING-GEAR TRAIN
moved from the gear train without remov-
105. Description
ing the gear cover. The reamining gears, with
The timing-gear train is located at the same
the execption of the crankshaft gear, can be re-
end of the engine as the flywheel, and is en-
moved after the gear cover is removed.
closed in a gear cover. It comprises the gover-
nor gear, camshaft gear, crankshaft gear, idler
106. Removal of Timing-Gear Train
gear, oil-pump gear, and magneto gear. The
a. Remove the gear cover (17, fig. 28) and
magneto gear and the governor gear can be re-
t h e spacer (14).
