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TM 9-8000
breaker contact points. Two-circuit operation particularly
is adaptable to V-type engines, with each set of contacts
taking care of one bank of cylinders. Because each set
of breaker contacts is independent of the other
electrically, the breakers require synchronizing for proper
operation.  On some V-type engines, the two breaker
arms open at Irregular Intervals, and therefore the
manufacturer's specifications should be checked before
any attempt is made to adjust the contact points.
e. Dual (Twin) Ignition (Fig. 15-15). Practically all
automobiles have single Ignition (one spark plug in each
cylinder), although dual ignition has been used to
advantage.  No particular new theory is Involved in
producing and delivering current to the spark plugs In
dual Ignition. The principal difference is the use of two
sparks to fire the fuel charge at two separated points
within the same cylinder. If two sparks are delivered at
widely separated points at the same Instant, the fuel
charge will start to burn from two points and meet in the
center,  thus  securing  more  rapid  and  complete
combustion.  The firing of two spark plugs in each
cylinder from one current source is sometimes called
twin Ignition. The dual Is provided with two coils and two
breaker arms operating on two circuits to supply sparks
Figure 15-13. Alternately Actuated
to two sets of spark plugs. To obtain the full advantage
Multiple Contacts.
of  dual  ignition,  the  breaker  contacts  must  be
synchronized to fire two sparks simultaneously In each
spark plugs. The breaker contacts operate alternately,
cylinder. The rotor segments then will deliver sparks to
but have no electrical connection between them except
two opposite terminals In the distributor head, which are
their common ground. This Ignition interrupter permits
connected on two spark plugs within the same cylinder.
two separate ignition systems: one system operating for
Each rotor segment fires alternate terminals around the
one half of the cylinders and the other system for the
head; one segment firing the spark plugs on the right
other half. Here, the relation between the two sets of
side of the cylinders and the other segment firing the
contacts is one of timing only, so that each will operate at
spark plugs on the left side of the cylinders.
the correct instant for the cylinders it serves.
Transistorized Point Ignition (Fig. 15-16).
(2)  The distributor must take care of the two
circuits. The high-tension lead from one coil enters the
a. General. The transistorized point Ignition system
center of the distributor head al terminal 1 (figure 15-14),
operates much the same way as the conventional
while the high-tension lead from the other coil enters at
Ignition system.  The difference Is the addition of a
terminal 2, which Is connected to a small ring that
transistor to carry coil current. The purpose of this
surrounds the central terminal. Two separate segments
Ignition system is to lengthen the life of the contact
are molded within a double arm rotor, each one In
points, which are traditionally the most troublesome
contact with one of the high-tension terminals One rotor
component of the Ignition system.
segment completes Its circuit to alternate spark plug
terminals In the distributor cap the other rotor segment
taking the Intervening terminals.  Thus, there are two
separate secondary circuits, 1 and 2, each furnishing
current to half the spark plugs. The sparks from each
coil are produced In exactly the same way as they are in
a single system because each coil has Its own set of


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