Chevrolet Light Duty Truck 1973, Service Manual

Page: 578 / 979

6 Y -5 0 ENGINE ELECTRICAL
Wet, oily deposits with a minor degree of electrode wear may be caused by oil
pumping past worn rings. “Break-in” of a new or recently overhauled engine before
rings are fully seated may also result in this condition. Other possibilities of intro­
duction of oil into the combustion chamber are a porous vacuum booster pump
diaphragm or excessive valve stem guide clearances.
Usually, these spark plugs can be degreased, cleaned and reinstalled.
A HOTTER TYPE SPARK PLUG WILL REDUCE OIL DEPOSITS,
but too hot a
spark plug can cause pre-ignition and, consequently, severe engine damage. An engine
overhaul may be necessary in severe cases to obtain satisfactory service.
OIL FOULING
O il Fouling
HEAT SHOCK FAILURE
Heat shock is a common cause of broken and cracked insulator tips. Over­
advanced ignition timing and low grade fuel are usually responsible for heat shock
failures. Rapid increase in tip temperature under severe operating conditions causes
the heat shock and fracture results.
Another common cause of chipped or broken insulator tips is carelessness in
regapping by either bending the centerwire to adjust the gap, or allowing the gapping
tool to exert pressure against the tip of the center electrode or insulator when
bending the side electrode to adjust the gap.
ELIMINATE THE CAUSE AND INSTALL A NEW PLUG OF THE RECOM­
MENDED HEAT RANGE.
Heat Shock Failure
STARTER SYSTEM
INDEX
General Description.................................... ................... 6Y-50 No Cranking Action.................................................... . 6Y-57
Theory of Operation................................... ................... 6Y-51 Cranking Speed Abnormally Low........................... . 6Y-57
Starter Motor.............................................. ................... 6Y-51 Voltage Test of Starting System and Solenoid
Solenoid......................................................... ................... 6Y-53 Switch................................................................................... . 6Y-57
Service Operation......................................... ................... 6Y-55 Amperage Test of Solenoid Switch Windings.... . 6Y-58
Lubrication................................................... ................... 6Y-55 Checking Pinion Clearance......................................... 6Y-58
Starter Motor Replacement.................... ................... 6Y-55 Bench Test of Starting Motor.................................. . 6Y-59
Diagnosis......................................................... ................... 6Y-57 Diagnosis Chart.............................................................. . 6Y-60
GENERAL DESCRIPTION
The function of the starting system, composed of the
starting motor, solenoid and battery, is to crank the
engine. The battery supplies the electrical energy, the
solenoid completes the circuit to the starting motor, and
the motor then does the actual work of cranking the
engine.
The starting motor (fig. Is) consists primarily of the
drive mechanism, frame, armature, brushes, and field
windings. The starting motor is a pad mounted 12-volt
extruded frame type, having four pole shoes and four
fields, connected with the armature. The aluminum drive
end housing is extended to enclose the entire shift lever
LIGHT DUTY TRUCK SERVICE MANUAL