Section XI. MAINTENANCE OF IGNITION SYSTEM

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

(para 4-30).

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.

paragraph 4-19a.

(3) Inspect the fan guard and fan shroud for

(3)

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).

Section XI. MAINTENANCE OF IGNITION SYSTEM

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

burning.

4-33