TM 55-4920-384-13&P
Turn the engine over several times with the starting
nut and capscrew for mounting the magneto, making
crank to distribute the oil over the cylinder walls,
sure the magneto flange gasket is in place.
Then replace the spark plugs and compression should
The No. 1 terminal is the upper right hand tower on
be satisfactory.
the magneto cap. The terminals follow the proper fir-
ing order of 1-3-4-2 in a clockwise direction viewing
HIGH TEMPERATURE SAFETY SWITCH
the cap end. The leads from the magneto should be
As a safety precaution against overheating, some en-
connected to spark plugs of corresponding numbers,
gines have a high temperature safety switch mounted
see "Firing Order" paragraph.
on the cylinder head near the No. 2 spark plug. This
When the magneto is properly timed the impulse coup-
switch will automatically stop the engine when head
ling will snap when the `DC' and `X' marked vane of
temperatures rise beyond a safe degree.
the flywheel, lines up with the mark on the flywheel
The switch is set by the manufacturer to operate at
which should indicate the centerline of the No. 1 and
a predetermined temperature, and consequently, should
3 cylinders. This can be checked by turning crank-
not be tampered with. If an unusually high cylinder
shaft over slowly by hand. The impulse will also snap
head temperature causes the switch to automatically
every 180 of flywheel rotation thereafter,
short out the magneto and stop the engine, a waiting
The proper spark advance is 23. To check timing
period of about 15 minutes will be required before the
with a neon light, the running spark advance is indi-
switch has cooled off sufficiently to allow the engine
to be re-started. An overheated engine will score the
cated by a l/8" diameter hole on the flywheel shroud,
23 before vertical centerline of the No. 1 and 3
cylinder walls, burn out connecting rod and crank-
cylinders. See Fig. 14. The end of the `X' m a r k e d
cause of the overheating condition will have to be
vane should be whitened with chalk or paint for this
remedied before the engine is re-started. See E n g i n e
operation.
Overheats paragraph in Troubles, Causes and Reme-
The magneto rotates at crankshaft speed in clockwise
dies section.
direction when viewing driving gear end of magneto.
The magneto distributor rotor turns at half engine
speed.
TROUBLES
CAUSES AND REMEDIES
FIRING ORDER
The firing order of the cylinder is 1-3-4-2, and the
Three prime requisites are essential to starting and
magneto distributor rotor turns at one-half engine
maintaining satisfactory operation of gasoline en-
speed, as is the, case with conventional `in line' e n -
gines. They are:
gines. The intervals between the firing of the cylin-
ders is 180. No. 1 cylinder is the one nearest to the
1. A proper fuel mixture in the cylinder.
flywheel in the left bank of cylinders, when viewed
2. Good compression in the cylinder.
from the flywheel end of the engine. No. 3 cylinder is
the other cylinder in this bank. No. 2 cylinder is the
3. Good spark, properly timed, to ignite the mixture.
one nearest to the flywheel in the right bank of cylin-
If all three of
these conditions do not exist, the en-
ders and No. 4 is the other cylinder in this bank. The
gine cannot be
started. There are other factors which
cylinders are numbered from 1 to 4 on the sir shroud
will contribute
to hard starting; such as, too heavy
near the spark plugs, see Figs. 1 and 2. The flywheel
a load for the
engine to turn over at a low starting
end of the engine is designated the front end, and the
power take-off end, the rear end of the engine.
etc. These conditions may affect the starting, but do
not necessarily mean that the engine is improperly
SPARK PLUGS - RADIO SHIELDED
adjusted.
The spark plug gap should be thirty thousandths
As a guide to locating any difficulties which might
(.030) of an inch, and plugs should be kept clean both
arise the following causes are listed under the three
inside and out. The spark plug thread is 18 millimeter.
headings: Fuel Mixture, Compression and Ignition.
Be sure to use a good gasket under the spark plug.
In each case the causes of trouble are given in the
Tighten spark plugs, 25 to 30 foot pounds torque. Re-
order in which they are most apt to occur. In many
fer to Engine Parts List section for part numbers of
cases the remedy is apparent, and in such cases no
replacement spark plugs.
further remedies are suggested.
RESTORING COMPRESSION
STARTING DIFFICULTIES
On a new engine or on one which has been out of op-
eration for some time, the oil may have drained off
FUEL MIXTURE
the cylinder so that compression will be weak. This
may cause difficulty in starting. To remedy this con-
No fuel in tank or fuel shut-off valve closed.
dition, remove the spark plugs and pour about a fluid
Fuel pump diaphragm worn out, so pump does not
ounce of crankcase oil through the spark plug hole
supply carburetor with fuel.
into each cylinder.
D-14