f. Testing. Test the solenoid coil as in d above. Connect a voltmeter across the coil terminals. Insert all the
resistance into the circuit and then decrease resistance slowly until the switch closes. Note the closing voltage. Increase
the resistance and not the opening voltage. The switch should close at not more than 10 volts and open at from 0.5 to 3
volts. Refer to d above if the switch does not meet specifications.
g. Installation. Refer to paragraph 99b.
Section IX. DISTRIBUTOR AND COIL
200. Description
a. Distributor. The distributor provides current to the primary winding of the ignition coil at the proper time, and also
distributes the high tension voltage to the proper spark plug. The breaker contacts of the distributor are connected in the
coil primary circuit so that the rotation of the cam opens the coil circuit at the proper instant to generate a spark. The
distributor cap and rotor are arranged so that the high tension voltage is connected to the correct spark plug for firing each
cylinder. The distributor has centrifugal governor control of the timing, and the cam is connected to the drive shaft through
the governor. This is arranged so that as the speed is increased, the relationship of the cam to the breaker arm is
changed by the centrifugal governor action. The rate or amount of spark advance is controlled by the weight springs and
the centrifugal governor.
b. Ignition Coil. The ignition transforms the low voltage supplied by the batteries into the high voltage needed to jump
the spark plug gap. The coil has two windings, one the primary winding which consists of a comparatively few turns of
heavy wire, and the secondary winding which consists of many turns of very fine wire. The secondary winding is wound on
a soft iron core, while the primary winding is wound around the outside of the secondary winding. A soft iron shell
encloses the outside of both windings and serves to complete the magnetic circuit. Carefully selected and tested
insulation is placed between the winding layers, the primary and secondary windings, and between the outside of the
primary winding and the soft iron shell. Whenever current is built up and broken in the primary winding, a voltage is
induced in the secondary winding. The design of the coil is such that the induced voltage will be high enough to produce a
spark at the spark plug.
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