TM 9-3431-254-14&P
The magneto is driven at crankshaft speed in clock-
wise direction when viewing gear end of magneto. The
magneto distributor rotor turns at half engine speed.
Magneto breaker point gap is 0.015 inch at full sepa-
ration. If the ignition spark becomes weak after con-
tinued operation, the breaker points may have to be
readjusted or replaced. Refer to Manufacturer's Bul-
letin in rear of manual for service and adjustment of
breaker points.
If difficulty is experienced in starting the engine or
if engine misses firing, the strength of the ignition
spark may be tested as follows: Disconnect the cables
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from all towers on the distributor cap, except the
center coil tower. Insert a stiff piece of wire or metal
tighten plug until it begins to seat on the gasket,
rod into one of the sockets. Hold the terminal for this
then turn 1/2 to 3/4 of a turn more.
tower 1/8 inch from the wire or rod, as shown in Fig.
RESTORING COMPRESSION
tions with the hand crank and watch for a spark to
On a new engine or on one which has been out of op-
discharge during the cranking cycle.
eration for some time, the oil may have drained off
the cylinder so that compression will be weak. This
may cause difficulty in starting. To remedy this con-
dition, remove the spark plugs and squirt about a
fluid ounce of crankcase oil through the spark plug
hole into each cylinder.
Turn the engine over several times with the starting
crank to distribute the oil over the cylinder walls.
Then reassemble spark plugs and compression should
be satisfactory.
The clearance between the valve and rocker arm,
with the tappet in its lowest position (valve complete-
ly closed) and the engine cold:
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Repeat this check with each of the other ignition
Inlet
-0.008 inch
cables. A good spark at each of the towers will elimi-
Exhaust - 0.014 inch
nate the ignition coil and distributor as the source of
trouble. If there is a weak spark, or none at all, check
The rocker arms can be identified as follows: When
breaker point opening for 0.020 inch gap. It may be
facing the side of the engine, the exhaust rocker arm
necessary to install a new condenser, or the ignition
coil may be faulty.
The spark plugs should be removed periodically,
cleaned and re-gapped. Approximately every 350
hours of operation, replace spark plugs with new
plugs of correct heat range, like Champion 14 mm,
No
N-12Y or equal.
The width of the gap between the points of the two
electrodes must be very carefully and precisely set,
because incorrect settings will have an adverse af-
fect on engine operation. Check spark plug gap with
a wire type gauge and regap as shown in Fig. B-19.
Spark plug gap - 0.030 of an inch.
Use a new gasket when mounting either old or new
plugs and thoroughly clean threads in cylinder head
before installation. Tighten spark plugs to 22 foot
pounds torque. If torque wrench is not available,
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