Chevrolet 70 1969 Series, Shop Manual

Page: 382 / 913

IGNITION SYSTEM
ENGINE ELECTRICAL 6Y-11
GENERAL
The ignition system consists of the source of
power (battery or generator), ignition switch, igni­
tion coil, distributor, condenser, spark plugs, and
high and low tension wires.
A 1.52 ohm resistance wire is used in the
body wiring harness connecting the battery or ig­
nition terminal of the ignition switch to the igni­
tion coil on all vehicles equipped with the V-6
gasoline engine. The 1.52 ohm resistance wire is
identified on wiring diagrams in Section 12.
This resistance serves to increase ignition
coil efficiency and lengthen distributor point life.
If wire becomes damaged, it should be replaced
with wire of same gauge and length.
N O T E : The resistance value of wire can be
checked as explained later.
C A U T IO N : Since the ignition coil is fed
through the starter solenoid during cranking, the
engine will have a tendency to start whenever it is
cranked, even though the ignition switch is in the
“ O F F ” position. To prevent this from happening
and possibly causing serious injury, always dis­
connect the primary wire from the ignition coil
or pull the “ EN GIN E S T O P " knob out before per­
forming tests which require cranking the engine.
RESISTANCE WIRE OR UNIT CHECK
IM P O R T A N T : Before testing the resistance
wire or unit, make sure the ignition switch is in
the “ O F F ” position, otherwise damage to ohm-
meter will result.
1. Make sure ignition switch is in “ O F F ”
position.
2. Connect an ohmmeter lead to each end of
the resistance wire or unit and note reading.
3. If ohmmeter reading is not within 1.45 -
1.59 ohms, replace the resistance wire or unit.
IGNITION MAINTENANCE
Inspecting and adjusting the ignition system
at regular intervals will aid in locating and cor­
recting conditions which result in lowered per­
formance b e f o r e the engine performance is
seriously affected.
1. Check condition of battery and cables as
directed in “ B A T T E R Y ” section.
2. Check operation of centrifugal advance
mechanism by removing distributor cap and turn­
ing the rotor in clockwise direction. The cam
should rotate freely and when released, it should
return to its original position without sticking or
binding.
3. Wipe ou+ distributor cap with a soft cloth
and clean wire sockets with a small round brush.
Inspect cap and rotor for chips, cracks, and car­
bonized short paths; look for burned metal inserts
in cap and for burned metal segment on rotor.
4. Inspect breaker points. Slight discoloration
and roughness is normal. Slight roughness can be
removed with a few strokes of a clean, fine-cut
contact file. If points are badly pitted or burned,
replace points as directed later under "Distributor..
5. Check cam dwell angle with a dwell meter.
If dwell meter is not available, point opening can
be checked with a dial indicator. Never check open­
ing of used points with a feeler gauge. If dwell
angle (or point opening) requires adjustment, ad­
just as directed later under "Distributor."
6. Check ignition timing with timing light as
directed later under "Ignition Timing."
7. Inspect all ignition wiring for brittle, crack­
ed, or oil-soaked insulation. Check all connections,
making sure they are clean and tight.
8. Distributor must be kept properly lubri­
cated. Refer to LU B R IC A T IO N (SEC. 0) for inter­
vals and instructions.
9. Remove spark plugs and clean, inspect,
and adjust point gap as directed later under "Spark
Plugs."
IGNITION SWITCH REPLACEMENT
The ignition switch and harness-to-switch con­
nector features a three tang lock to secure a firm
connection (fig. 1). The switch lock cylinder and
cylinder housing can be removed as follows:
R E M O V A L
1. Disconnect negative cable from battery post.
2. Remove lock cylinder by positioning switch
in "lock" position and inserting wire in small hole
in cylinder face. Push in on wire to depress plung­
er and continue to turn key counterclockwise until
lock cylinder can be pulled from cylinder housing.
CHEVROLET SERIES 7 0 -8 0 H EAVY DUTY TRUCK SH O P M A N U A L