Chevrolet 70 Series 1970, Service Manual

Page: 555 / 841

ENGINE ELECTRICAL 6Y-14
IGNITION SYSTEM
GENERAL
The ignition sy stem c o n sists of the so u rc e of
pow er (battery o r g enerator) ignition sw itch, igni­
tion coil, d istrib u to r, condenser, s p a rk plugs, and
high and low tension w ire s.
A 1.52 OHM re sista n c e w ire is in sta lle d in the
engine w iring h a rn e ss on all vehicles equipped with
the V6 gasoline engine. T h is w ire is in stalle d
betw een the b a tte ry o r ignition te rm in a l on the
ignition sw itch and the (+) te rm in a l on the ignition
coil and is identified on W irin g D iag ram s in ap ­
plicable "W iring D iagram s" a s 20-WHT.-ORN. &
P P L . CR. TR.
The re s is ta n c e w ire is used to in c re a s e igni­
tion co il efficiency and lengthen d istrib u to r point
life. If re s is ta n c e w ire becom es dam aged, re p la ce
with w ire of sam e gauge and length.
IMPORTANT: DO NOT u se re g u la r copper
w ire in place of the re s is ta n c e w ire . When re p la c ­
ing a re s is ta n c e unit, use recom m ended p a r ts .
NOTE: R e sista n c e value of the w ire o r unit
can be checked as explained la te r in th is section.
CAUTION
Since the ignition coil is fed through
the s ta rte r solenoid during cranking, the
engine will have a tendency to s ta rt when­
ever it is cranked, even though the igni­
tion switch is in the "O F F " position. To
prevent this from happening and possibly
causing serious injury, always disconnect
the p rim a ry w ire from the ignition coil
before perform ing tests which require
cranking the engine._______________
RESISTANCE WIRE OR UNIT CHECK
IMPORTANT: B efore testing the re sista n c e
w ire o r unit, make s u re the ignition sw itch is in
the "O FF" position, otherw ise damage to ohm-
m e te r w ill re s u lt.
1. Make s u re ignition sw itch is in "O FF" p o si­
tion.
2. Connect an ohm m eter lead to each end of
the re s is ta n c e w ire o r unit and note reading.
3. If ohm m eter reading is not within 1.45 -
1.59 OHMS, re p la ce the re sista n c e w ire o r unit.
IGNITION MAINTENANCE
Inspecting and adjusting the ignition system
a t re g u la r in terv a ls w ill aid in locating and c o r­
re ctin g conditions which re s u lt in low ered p e r ­
form ance before the engine p erfo rm an ce is s e r ­
iously affected.
1. Check condition of b attery and cables as
d irec ted in "BATTERY" section.
2. Check operation of centrifugal advance
m echanism by rem oving d istrib u to r cap and tu rn ­
ing the ro to r in clockw ise direction. The cam
should ro tate freely and when re le a se d , it should
re tu rn to its original position without sticking o r
binding.
3. Wipe out d istrib u to r cap with a soft cloth
and clean w ire sockets with a sm all round brush.
Inspect cap and ro to r fo r chips, cra c k s, and c a r ­
bonized sh o rt paths; look fo r burned m etal in s e rts
in cap and for burned m etal segm ent on ro to r.
4. Inspect b re a k e r points. Slight discoloration
and roughness is norm al. Slight roughness can be
rem oved with a few stro k e s of a clean, fin e-cut
contact file. If points a r e badly pitted o r burned,
re p la ce points as d irec ted la te r under "D istributor'.’
5. Check cam dwell angle with a dwell m eter.
If dwell m e te r is not available, point opening can
be checked with a dial in d icato r. Never checkopen-
ing of u sed points with a fe e le r gauge. If dwell
angle (or point opening) re q u ire s adjustm ent, ad ­
ju st as d irected la te r under "D istrib u to r.”
6. Check ignition tim ing with tim ing light as
d irec ted la te r under "Ignition Tim ing."
7. Inspect all ignition w iring fo r b rittle , c ra c k ­
ed, o r o il-so ak ed insulation. C heckall connections,
m iking s u re they a r e clean and tight.
8. D istrib u to r m ust be kept p ro p e rly lu b ri­
cated. R efer to LUBRICATION (SEC. 0) of this
m anual, fo r in terv a ls and instru ctio n s.
9. Remove sp a rk plugs and clean, inspect,
and adjust point gap as d irected la te r under "Spark
P lu g s."
IGNITION SWITCH REPLACEMENT
The ignition o r control sw itch a n d h a rn e s s -to -
sw itch connector fe a tu re s a th ree tang lock to s e ­
c u re a firm connection (fig. 1). The sw itch lock
cylinder and cylinder housing can be rem oved as
follows:
REMOVAL
NOTE: On conventional cab and S e rie s 70-80
T ilt cab m odels, it may be n e c e ssa ry to rem ove
instru m en t c lu s te r retaining screw s and tilt
c lu s te r outw ard to gain a c c e ss to ignition o r con­
tro l switch.
On s e r ie s 90 Alum. T ilt Cab vehicles, r e ­
move a c c e s s panel from console to gain a c c e ss to
control switch.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL