Chevrolet Light Duty Truck 1973, Service Manual

Page: 579 / 979

EN G IN E ELECTRICAL 6Y-51
CO NTACT
FINGER
SOLENOID
TURN SPRING
SHIFT
LEVER
P IN IO N
STOP
BRUSH INSULATED BRUSH HOLDER \ FIELD COIL
BRUSH SPRING ARM ATURE
GRO UNDED BRUSH HOLDER
O V E R R U N N IN G
ASSIST CLUTCH
SPRING
Fig. I s — S ta r tin g M o to r C ross S e ction (T y p ic a l)
and plunger mechanism, protecting them from dirt, drive end bearing. The flange mounted solenoid switch
splash, and icing. The drive end frame also includes a operates the overrunning clutch drive by means of a
grease reservoir to provide improved lubrication of the linkage to the shaft lever.
THEORY OF OPERATION
The starting system is made up of the cranking motor
with its drive mechanism, the starter motor solenoid and
the Energizer, (often referred to as the Battery). These
units are connected together and work as a team to crank
the engine. The simplified diagram (Fig. 2s) shows the
electrical components in a typical starting system.
Although modern day applications use more circuitry
and controls than shown in Figure Is, the function of the
components is always the same—to convert electrical
energy from the Energizer into mechanical energy at the
starter motor to crank the engine.
STARTER MOTOR
To understand the operating principles of a starter
motor, think of a straight wire conductor located in the
magnetic field of a horseshoe-shaped magnet. Current is
flowing through the wire as shown in Figure 3s. There
will be two separate magnetic fields—the one produced
by the horseshoe magnet and the one produced by the
current flow through the conductor.
Since magnetic lines always leave a North pole and enter
a South pole, the direction of the magnetic lines between
the two poles of the horseshoe magnet will be upward as
shown. The current-carrying conductor will produce a
magnet field shown as circles around the wire. The net
result is more magnetic lines on the left hand side of the
wire than on the right (Fig. 4s).
With a strong field on one side of the conductor and a
weak field on the other side, the conductor will move
from the strong to the weak field, or from left to right.
This magnetic force makes the cranking motor operate.
A basic motor is shown in Figure 5s. A loop of wire is
placed between two iron pole pieces and is connected to
two separate commutator bars. Riding on the commuta­
tor bars are two brushes, which are connected to the
battery and to the windings located over the pole pieces.
Current flow can be traced from the battery through the
pole piece windings, to a brush and commutator bar,
through the loop of wire to the other commutator bar
and brush, and then back to the battery. The magnetic
fields create a turning or rotational effect in the same
clockwire direction as shown in Figure 6s.
The basic motor we have used in our illustrations has no
LIGHT DUTY TRUCK SERVICE MANUAL