Quantcast Section XI. MAINTENANCE OF IGNITION SYSTEM - TM-5-4320-234-120063


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Figure 4-18. Radiator and related parts, exploded view.
TM-5-4320-234-12 Pump Centrifugal Self-Priming Gasoline Engine Driven Wheel Mounted 6-Inch 1500 GPM Capacity At 60 Foot Head Manual
Spark Plugs - TM-5-4320-234-120064
4-32. Radiator
b. Cleaning and Inspection.
a. Removal.
(1)  Thoroughly flush the radiator with water,
both inside and out. Make sure all bugs and debris are
(1)  Drain the radiator and oil cooler, and
removed from the external cooling fins.
remove the coolant and oil cooler lines from the radiator
(2)  Inspect the radiator for cracks, damaged
cooling fins, leaking tubes, leaks around the top bonnet,
(2) Remove the engine housing as necessary to
and other damage. Refer a damaged radiator to direct
provide access to the radiator for removal. Refer to
support maintenance for repair.
(3) Inspect the fan guard and fan shroud for
Remove the fan guard (3, fig. 4-18).
cracks,  broken  weldments,  distortion,  and  other
Remove the machine screws (4) and lock washers (5)
damage. Replace damaged parts.
and remove the supports (6 and 7).  Remove the
c. Installation.
machine screws (8), lock washers (9) and flat washers
(1)  Installation is the reverse of the removal
(10), and remove the fan shroud (11).
procedure. Refer to figure 4-20.
(4) Use a rope sling and a hoist to support the
(2) Install the coolant and oil cooler lines and
weight of the radiator before removing the nuts (12) and
fittings (para 4-30).
lock washers (13) that secure the radiator (21) to the
(3) Install the engine housing panels that were
engine support; remove the radiator and liners (14).
removed to provide access to the radiator (para 4-19c).
(5) Remove the nuts (15), lock washers (16)
(4) Service the engine coolant system and the
and flat washers (17), and remove the crank support
engine oil system. Start the engine and check for leaks.
(18) and spacer (19) from the radiator. Remove the
Correct any deficiencies
radiator cap (20).
4-33. Description
d.  The voltage induced in the secondary coil is
applied to the spark plug of the required cylinder at
a. The ignition system includes the magneto (11,
precisely the correct instant by the distributor rotor in the
fig. 4-7) and radio-suppressed spark plugs (1) which
magneto.  The breaker points open at the required
have shielded cables (5).  The system is completely
instant to ensure a hot spark to the spark plug at this
independent of the battery- and alternator-powered
time. The spark at the spark plug causes the ignition of
electrical system.
the fuel-air mixture in the cylinder.
b. The magneto is timed to the engine and is driven
e. At starting, an impulse coupling on the magneto
by the camshaft gear through the governor drive gear
causes a snapping action of the magneto rotor,
which is engaged by the drive lugs on the magneto drive
producing the rapid rotation necessary to energize the
coupling. There is a critical timing relationship between
electrical windings.  This retards the rotation of the
these driving parts since it determines the instant at
magneto rotor at slow speeds until top-dead-center is
which the spark from the magneto will be delivered to
reached. Spring action then snaps the rotor forward to
each spark plug.  An improperly timed magneto will
produce the required high rotational speed.
make engine operation impossible.
f.  The magneto also contains automatic spark
c. The magneto consists of a magnetic rotor which
advance provisions so that the spark will occur sooner
is rotated in a laminated frame to set up magnetic flux in
during high speed operation.  This is necessary for
the laminated frame.  This induces a current in the
smooth engine performance.  The automatic spark
primary winding each time the magnetic flux rises and
advance rotor has pawls which are thrown outward as
falls. The primary winding acts as the primary winding
engine speed increases to change the relationship of the
of a step-up transformer, surrounded by the secondary
distributor rotor in the magneto.
coil. Breaker point opening occurs at the instant of
g. The connections to the distributor block of the
maximum primary current, causing an immediate
magneto are shielded by a cover through which the
collapse of the magnetic field. This collapsing magnetic
high-tension spark plug cables pass. The cable shields
field induces an extremely high voltage surge through
are secured to the cover, but the electrical conductors
the secondary circuit.  The capacitor in the primary
pass through and connect to the distributor block.
circuit speeds the collapse of the circuit, increasing the
secondary voltage and also reducing contact point

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