Cranking Circuit; Description And Operation - Pontiac FIREBIRD 1972 Service Manual

ENGINE ELECTRICAL 6E-5
DESCRIPTION AND OPERATION
CRANKING CIRCUIT
The cranking circuit consists of the battery, starting mo-
tor, ignition switch, and related-electrical wiring. These
components are connected electrically as shown in Fig.
STARTING MOTOR
All starting motors are 12-volt extruded frame-type units
of the enclosed shift lever design (Fig. 6E-4). This motor
has the shift lever mechanism and solenoid plunger en-
closed in the drive housing protecting them from exposure
to dirt, icing conditions, and road splash.
The starting motors used on 6-cylinder and 307 V-8 en-
gines have four poles and four field coils. The field circuit
used in these motors is a "series" type. The starting motor
used on 350 (V-8) engines has one shunt coil connected in
series from the motor terminal directly to ground and
three series coils connected in series from the motor termi-
nal to the insulated brushes. The starter motor used on all
400 & 455 (V-8) applications consists of two series con-
nected coils connected in parallel with a second set of two
series connected coils from the motor terminal to the in-
sulated brushes (Fig. 6E-5).
The brush rigging has brush arm supports attached di-
rectly to the extruded section of the field frame. One
ground brush and one insulated brush are both pivoted
from the same brush holder support, thus only two brush
holder supports are required. A single ribbon-type spring
applies tension to each pair of brushes.
An overrunning clutch type drive is used to engage the
cranking motor pinion with the flywheel (Fig. 6E-6).
Overrunning action of the clutch protects the cranking
motor armature from excessive speed when the engine
fires.
The armature shaft and clutch have mating spiral splines
which aid in meshing of the gears and thus prevent trans-
mission of cranking power until the clutch pinion is fully
engaged in the flywheel ring gear. A special assist spring
is located around the armature shaft between the end fiber
of the armature and the collar of the clutch drive. This
spring aids the solenoid in overcoming the return spring
COLLAR CLUTCH SPRING ROLLER SPRING
I
SHELL AND
LOCK WIRE SLEEVE ASSEMBLY
COLLAR
R
Fig. 6E-6 Overrunning Clutch
1
OMMUTATOR
(FIELD COILS
COILS
POLE COILS
307 V-8 AND
6 CYL. ENGINE
SHOE
V-8 350 ENGINES
SERIES
COIL (4)
SHOE
V-8 400 6 455 ENGINES
Fig. 6E-5 Starting Motor Internal Circuits