Buick LeSabre 1965 Service Manual page 604

1 0 - 3 4 IGNITION SYSTEM ELECTRICAL SYSTEMS
through a window in the distrib-
utor cap while the engine is idling.
Any accurate dwell meter may be
used. See paragraph 10-34 for
adjustment procedure.
The distributor is of the single
contact type with an 8-lobe cam.
High speed operation is improved
by an especially l i g h t contact
breaker arm and a high speed
cam. Maximum operating effi-
ciency of the engine is obtained
under all speed and load condi-
tions by the centrifugal advance
mechanism, which i s l o c a t e d
above the circuit breaker cam
inside the rotor, and the vacuum
advance mechanism built into the
distributor. See Figure 10-34.
The contact point set is replaced
as one complete assembly. The
service replacement contact set
has the breaker lever spring ten-
sion and point alignment adjusted
lit the factory. Only the point
opening requires adjusting after
replacement.
5
- Spark Plugs. AC spark plugs
having 14 MM threads, short (3/8")
terminals, and .035" gaps are
specified. For service informa-
tion on spark plugs and wires, see
paragraph 10-36.
6. Radio Suppression. All sec-
ondary wiring has a resistance of
4000 ohms per foot so that it is
unnecessary to install a suppres-
sor on the high tension cable when
a radio is installed. A capacitor
is mounted on the side of ignition
coil and connected to the positive
(battery) terminal of coil when a
radio is installed.
An additional capacitor must
never be connected to the distri-
butor terminal as this will cause
excessive pitting of b r e a k e r
points or engine missing.
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b. Ignition Operating Circuits
To clarify operating principles
as well as to simplify the process
Figure 10-34—Distributor and
Cap Assembly
of tracing troubles, the parts of
the ignition system should be
understood to provide two sepa-
rate and distinct circuits, as
follows:
1. The Primary Circuit carries
the low voltage current supplied
by the battery or generator. In
addition to these sources of elec-
trical energy, the primary circuit
contains the ignition switch, igni-
tion coil resistance unit, primary
winding of the ignition coil, dis-
tributor contact points, conden-
ser, and all connecting low tension
wiring.
2. The Secondary Circuit car-
ries the high voltage surges pro-
duced by the ignition coil, which
result in high voltage spark be-
tween the electrodes of the spark
plugs in engine cylinders. This
circuit contains the secondary
winding of the ignition coil, coil
to distributor high tension lead,
distributor rotor and cap, ignition
cables, and spark plugs.
c. Cycle of Operation
When the ignition switch is turned
on and the distributor contact
points are closed, battery or gen-
erator current flows through the
primary winding of the coil and
through the contact points to
ground. T h i s flow of current
through the primary winding of
the coil produces a magnetic field
around the coil windings and
thereby stores electrical energy
in the coil.
When the contact points are sepa-
rated by the revolving distributor
cam, the primary circuit is brok-
en. The condenser absorbs the
current which tends to surge
across the gap as the points sepa-
rate, thereby producing a sharp
break in the flow of current. If
the flow of current were not
sharply broken it would form an
arc which would burn the points
badly and would also drain away
most of the energy stored in the
coil. There would be insufficient
energy left in the coil to produce
the necessary high voltage surge
in the secondary circuit.
The very rapid change in strength
of the magnetic field when the
primary circuit is sharply broken
causes a high voltage to be in-
duced in every turn of both the
primary and secondary windings.
The high voltage surge produced
in the secondary winding of the
coil travels through the cable to
the center of distributor cap,
through the rotor to the adjacent
distributor cap segment from
which it is conducted to the pro-
per spark plug by the ignition
cable. The high voltage surge
jumps the gap between the in-
sulated center electrode and the
grounded side electrode of the
spark plug, thus producing the
spark r e q u i r e d to ignite the
charge in the selected combustion
chamber of the engine.
As the spark appears at the spark
plug gap the energy in the coil
begins to drain from the coil
through the secondary circuit,
thus sustaining the spark for a