Section Xll. MAINTENANCE OF ELECTRICAL SYSTEM

at the No. 6 firing position. Hold the magneto drive shaft at this position.

(4) Check the governor drive gear to make sure that the punch-marked tooth in the cam gear is engaged

between the two punch-marked teeth on the governor drive gear.

(5) Remove the magneto from the vise.

Turn the magneto drive lugs of the impulse coupling

counterclockwise about one-quarter turn so that the lugs will mesh with the drive members of the governor drive gear.

Position the magneto (23, fig. 4-21), spacer (25), and gasket (24) on the engine with the magneto lugs engaged and

tighten the mounting bolts moderately. Connect the spark plug cables.

(6) Start the engine and idle it at 600 rpm.

If the engine fails to start, it is probably due to faulty ignition timing. Recheck as directed above.

(7) With the engine running at 600 rpm, use a timing light connected to the rear spark plug and check that the

IGN-M indication on the flywheel is alined with the timing pointer. If it is not exactly alined, rotate the magneto slightly

until the correct indication is attained. Tighten the mounting bolts firmly.

Section Xll. MAINTENANCE OF ELECTRICAL SYSTEM

4-35. Description

a. The electrical system includes the battery box which houses two 12-volt, lead-acid-type storage batteries (3, fig.

4-1) connected in series to power the 24-volt electrical system. Battery output is used to energize the electrical starter (7,

fig. 4-26) to start the engine. The battery charge is partially depleted as the engine is started and is restored by the

battery charging system consisting of the alternator (1) and voltage regulator (10).

b. The alternator and regulator are typical automotive type in which the alternator output is controlled through the

voltage regulator, depending upon the state of charge of the battery.

When the battery charge is low, the voltage regulator increases the strength of the alternator field to increase the output

of the alternator. When the battery charge is normal, the output of the alternator decreases to near zero.

c. Reverse polarity connections to an alternator can severely damage the alternator. To prevent this damage, the

system is protected by a reverse polarity protector (9) which is mounted on the panel next to the voltage regulator.

Caution: Though this engine is equipped with a reverse polarity protector to protect the alternator against

damage due to reverse polarity connections, it is good practice to take special precautions when connecting

and disconnecting electrical leads and cables. Do not ground the field terminal between the alternator and

regulator. Do not operate the alternator in an open circuit with the rotor winding energized. Do not ground the

alternator output circuit. Take care to prevent reversing polarity of the electrical system. When using a battery

booster or fast charger, make sure the leads are connected with proper polarity. Failure to follow these

instructions may damage the alternator rectifiers, voltage regulator, and wiring.

d. The engine starter (7, fig. 4-26) is a solenoid-operated type in which the soleonid switch (6) is mounted on the

top of the starter. The solenoid switch uses electrical energy to pull the starter drive into engagement with the flywheel

ring gear and to make the electrical circuit which energizes the starter after the drive is engaged. When the engine

starts, the starter drive is disengaged, preventing the engine from driving the starter since engine operating speeds could

severely damage the starter. Reengagement of the starter while the engine is running is prohibited by the starter

disengage relay (para 4-42e).

4-36. Battery Charging Circuit Testing

Note. To determine if the alternator and voltage regulator are producing proper output to maintain the proper battery

charge, perform the on-engine tests described in this paragraph.

a. Battery Voltage and Shorted Isolation Diode Tests. These tests determine if the batteries are properly connected

to the alternator and if the isolation diode is shorted. A shorted isolation diode will discharge the battery through the

voltage regulator to ground.

(1) With the engine stopped, the battery disconnect switch positioned to ON, and the ignition switch positioned

to OFF, the electrical circuit will be as shown in figure 4-27.

(2) With a voltmeter, check the voltage across the negative output terminal of the alternator and the positive

terminal of the one battery which does not have its negative terminal grounded. Note the voltage. It should be 24.0 to

25.2 volts.

4-29