ENGINE 6-2
remotely at the starter, with a special jumper
cable or other means, the primary distributor
lead must be disconnected from the negative
post on the coil and the ignition switch must be
in the "ON" position. Failure to do this will
result in a damaged grounding circuit in the
ignition switch.
3.
Crank engine through at least four compression
strokes to obtain highest possible reading.
4.
Check and record compression of each cylinder.
5.
If one or more cylinders read low tor uneven, inject
about a tablespoon of engine oil on top of pistons
in low reading cylinders (through spark plug
port).
Crank engine several times and recheck
compression.
• If compression comes up but does not necessarily
reach normal, rings are worn.
• If compression does not improve, valves are
burnt, sticking or not seating properly.
• If two adjacent cylinders indicate low compres-
sion and injecting oil does not increase compres-
sion, the cause may be a head gasket leak between
the cylinders. Engine coolant and/or oil in cylin-
ders could result from this defect.
NOTE: If a weak cylinder cannot be located
with the compression check, see "Cylinder Bal-
ance Test" under "Additional Checks and Adjust-
ments" in this section.
Service and Install Spark Plugs (Fig. 2)
1.
Inspect each plug individually for badly worn elec-
trodes,
glazed, broken or blistered porcelains and
replace plugs where necessary. Refer to spark plug
diagnosis information presented in Section 6Y for an
analysis of plug conditions.
2.
Clean serviceable spark plugs thoroughly, using an
abrasive-type cleaner such as sand blast. File the
center electrode flat.
3.
Inspect each spark plug for make and heat range. All
plugs must be of the same make and number.
4.
Adjust spark plug gaps to specifications using a
round feeler gauge.
PORCELAIN
INSULATOR
INSULATOR CRACKS
OFTEN OCCUR HERE
CENTER ELECTRODE
[FILE FLAT WHEN
ADJUSTING GAP-
[DO NOT BEND!
(PROPER GAP)
(BEND TO ADJUST GAP)
CAUTION:
adjust gap.
Fig.
2 - Spark Plug Detail
Never bend the center electrode to
Always adjust by bending ground or
side electrode.
If available, test plugs with a spark plug tester.
Inspect spark plug hole threads and clean before in-
stalling plugs. Corrosion deposits can be removed
with a 14 mm. x 1.25 SAE spark plug tap (available
through local jobbers) or by using a small wire brush
in an electric drill. (Use grease on tap to catch
chips.)
ADJUST DWELL
ANGLE SETTING OR
POINT OPENING
Fig.
1 - Checking Compression
Fig.
3 - Distributor (In Line)
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE
6-3
(ROUND) Y~~fll^H
CENTRIFUGAL
A ^k
ADVANCE--jflgKpl
MECHANISM
UB|
CAM
KSK^2
LUBRICATOR
VlSMi
REPLACEMENT
^BK
-^ADJUST
SQUARELY
AND
JUST
TOUCHING
LOBE
OF
CAM
/ROTOR
HBB
__
I^BH^F
?
(SOUARE)
^K^ I /—
CAM
jKft^J / LUBRICATOR
H^T^
CAUTION!
QV NEVER
OIL
•L-^
CAM LUBRICATOR-
REPLACE
WICK
WHEN
NECESSARY
LATERAL
MISALIGNMENT
PROPER
LATERAL ALIGNMENT
Fig.
4- Distributor (V8)
CAUTION: Use extreme care
-when
using tap to
prevent cross threading. Also crank engine sev-
eral times to blow out any material dislodged
during cleaning operation.
7. Install spark plugs with new gaskets and torque to
specifications.
NOTE:
The following are some of the
greatest causes of unsatisfactory spark plug
performance.
•
Installation of plugs with insufficient torque to
fully seat the gasket.
•
Installation of the plugs using excessive torque
which changes gap settings.
•
Installation of plugs on dirty gasket seal.
•
Installation of plugs into corroded spark plug hole
threads.
8^ Connect spark plug wiring.
Service
Ignition System
1.
Remove distributor cap, clean cap and inspect for
cracks, carbon tracks and burned or corroded ter-
minals. Replace cap where necessary.
2.
Clean rotor and inspect for damage or deterioration.
Replace rotor where necessary.
3.
Replace brittle, oil soaked or damaged spark plug
wires.
Install all wires to proper spark plug. Proper
positioning of spark plug wires in supports is impor-
tant to prevent cross-firing.
4.
Tighten all ignition system connections.
5. Replace or repair any wires that are frayed, loose or
damaged.
Us
CORRECT
LATERAL MISALIGNMENT BY
j BENDING
FIXED CONTACT SUPPORT
[NEVER
BEND BREAKER LEVER
Fig.
5 - Point Alignment
Magnetic
Pulse(Breakerless)
Distributor
There are no moving parts in the ignition pulse ampli-
fier, and the distributor shaft and bushings have perma-
nent type lubrication, therefore no periodic maintenance
is required for the magnetic pulse ignition system. Refer
to Section 6Y for an analysis of problems and/or repair
procedures encountered on the Transistorized (Magnetic
Pulse) ignition system.
Standard
(Breaker Point) Distributor
(Figs.
3 or 4)
1.
Check the distributor centrifugal advance mechanism
by turning the distributor rotor in a clockwise direc-
tion as far as possible, then releasing the rotor to
see if the springs return it to its retarded position.
If the rotor does not return readily, the distributor
must be disassembled and the cause of the trouble
corrected.
2.
Check to see that the vacuum spark control operates
freely by turning the movable breaker plate counter-
clockwise to see if the spring returns to its retarded
position. Any stiffness in the operation of the spark
control will affect the ignition timing. Correct any
interference or binding condition noted.
3.
Examine distributor points and clean or replace if
riecessary.
DO
NOT SUCK
IN
TOO MUCH
ELECTROLYTE
TAKE
READING
AT
EYE LEVEL
Fig.
6 - Testing Specific Gravity of Battery
CHEVROtET
CHASSIS SERVICE MANUAL
ENGINE 6-4
• Contact points with an overall gray color and only
slight roughness or pitting need not be replaced.
• Dirty points should be cleaned with a clean point
file.
Use only a few strokes of a clean, fine-cut con-
tact file. The file should not be used on other
metals and should not be allowed to become
greasy or dirty. Never use emery cloth or sand-
paper to clean contact points since particles will
embed and cause arcing and rapid burning of
points. Do not attempt to remove all roughness
nor dress the point surfaces down smooth.
Merely remove scale or dirt.
• Clean cam lobe with cleaning solvent, lubricate
cam lobe with "Delco Remy Cam and Ball Bearing
Lubricant" or its equivalent and rotate cam lubri-
cator wick 1/2 turn.
• Replace points that are burned or badly pitted.
NOTE: Where prematurely burned or badly
pitted points are encountered, the ignition sys-
tem and engine should be checked to determine
the cause of trouble so it can be eliminated.
Unless the condition causing point burning or
pitting is corrected, new points will provide no .
better service than the old points. Refer to
Section 6Y for an analysis of point burning or
pitting.
• Check point alignment (fig. 5) then, adjust distri-
. butor contact point gap to .019" (new points) or
.016"
(used points). Breaker arm rubbing block
must be on high point of lobe during adjustment.
NOTE: If contact points have been in service,
they should be cleaned with a point file before
adjusting with a feeler gauge.
• Check distributor point spring tension (contact
Fig. 8 - Manifold Heat Control Valve (In Line)
point pressure) with a spring gauge hooked to
breaker lever at the contact and pull exerted at 90
degrees to the breaker lever. The points should
be closed (cam follower between lobes) and the
reading taken just as the points separate. Spring
tension should be 19-23 ounces. If not within
limits,
replace.
Excessive point pressure" will cause excessive
wear on the points, cam and rubber block. Weak
point pressure permits bouncing or chattering,
resulting in arcing and burning of the points and
an ignition miss at high speed.
4.
Install rotor and distributor cap. Press all wires
firmly into cap towers.
Fig. 7 - Checking Fan Belt Tension
Fig. 9 - Manifold Heat Control Valve (V8)
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE
6-5
Service Battery and Battery Cables
1.
Measure the specific gravity of the electrolyte in
each cell (fig. 6). If it is below 1.230 (corrected to
80°F.) recharge with a slow rate charger, or if de-
sired, further check battery.
2.
Connect a voltmeter across the battery terminals and
measure the terminal voltage of the battery during
cranking (disconnect the coil primary lead at the
negative terminal during this check to prevent engine
from firing). If the terminal voltage is less than 9.0
volts at room temperature, approximately 80°
±
20°
F.,
the battery should be further checked. See
Section 6Y for further tests.
3.
Inspect for signs of corrosion on battery, cables and
surrounding area, loose or broken carriers, cracked
or bulged cases,- dirt and acid, electrolyte leakage
and low electrolyte level. !Fill cells to proper level
with distilled water or water passed through a
"demineralizer".
The top of the battery should be clean and the bat-
tery hold-down bolts properly tightened. Particular
care should be taken to see that the top of the battery
is kept clean of acid film and dirt. When cleaning
batteries, wash first with a dilute ammonia or soda
solution to neutralize any acid present and then flush
off with clean water. Keep vent plugs tight so that
the neutralizing solution does not enter the cell. The
hold-down bolts should be kept tight enough to prevent
the battery from shaking around in its holder, but
they should not be tightened to the point where the
battery case will be placed under a severe strain.
To insure good contact, the battery cables should
be tight on the battery posts. Oil battery terminal
felt washer. If the battery posts or cable terminals
are corroded, the cables should be cleaned separately
with a soda solution and wire brush. After cleaning
and before installing clamps, apply a thin coating of
petrolatum to the posts and cable clamps to help
retard corrosion.
If the battery has remained undercharged, check
for loose or defective fan belt, defective Delcotron,
high resistance in the charging circuit, oxidized
regulator contact points, or a low voltage setting.
If the battery has been using too much water, the
voltage output
is-
too high.
Service Deicotron and Regulator
The Delcotron and regulator tests during tune up con-
sist of the above battery tests; the condition of the battery
indicating further tests and adjustments as outlined in
Section 6Y.
Service Belts (Fig. 7)
Inspect belt condition.
Check and adjust if necessary for correct tension of
belt, as follows:
• Using a strand tension gauge, check the belt tension.
• Adjust belt until the specified tension is reached.
(See Tune Up Chart.)
Service Manifold Heat Valve (Figs. 8 or 9)
Check manifold heat control valve for freedom of oper-
ation. If shaft is sticking, free it up with GM Manifold
Heat Control Solvent or its equivalent.
NOTE: Tap shaft end to end to help free it up.
Tighten Manifold
Tighten intake manifold bolts to specifications in the
FLAME
ARRESTOR
FLAME
ARRESTOR
NON-VENTED\
CAP
V\ VALVE
CLOSED
POSITIVE (283 & 327)
POSITIVE
(IN LINE)
POSITIVE
(327)
POSITIVE
(396 & 427)
Fig.
10 -
Crank case
Ventilation Systems
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE 6-6
CHOKE VALVE
COMPLETELY
CLOSED
PULL UPWARD ON
ROD TO END OF
TRAVEL
BEND ROD
TO ADJUST
ROD IN BOTTOM
OF SLOT
BOTTOM OF
ROD SHOULD
EVENWITH
TOP OF
HOLE
CHOKE VALVE
CLOSED
BOTTOM OF
ROD SHOULD
BE EVEN WITH
TOP OF HOLE
TOP OF ROD
SHOULD BE EVEN
WITH BOTTOM
OF HOLE (CHOKE
CLOSED)
^..BEND ROD TO
ADJUST
_PULL DOWNWARD
ON ROD TO CON-
TACT STOP
L6 (TYPICAL)
V8 327-275 HP
V8 350-295 HP
BEND ROI
TO ADJUST
PULL UPWARD ON
ROD TO CONTACT
STOP ON BRACKET
ALL V8 (EXCEPT 327-275 HP
AND 350-295 HP)
Fig.
11 - Remote Choke Adjustment
sequence outlined on Torque Sequence Chart. A slight
leak at the intake manifold destroys engine performance
and economy.
Service Fuel Lines and Fuel Filter
1.
Inspect fuel lines for kinks, bends or leaks and cor-
rect any defects found, • • •
2.
Inspect filter and replace if plugged.
NOTE:
If a complaint of poor high speed per-
formance exists on the vehicle, fuel pump tests
described in Section 6M should be performed.
Service Cooling System
1.
Inspect cooling system for leaks, weak hoses, loose
hose clamps and correct coolant level, and service
as required.
NOTE:
A cooling system pressure test, as de-
scribed in "Additional Checks and Adjustments"
in this section, may be performed to detect
internal or external leaks within the cooling
system.
Check and Adjust Accelerator Linkage
1.
Disconnect accelerator rod at carburetor throttle
lever.
2.
Hold carburetor throttle lever in wide position.
3.
Pull accelerator rod to wide open position. (On ve-
hicles equipped with automatic transmission, pull
through detent).
4.
Adjust accelerator rod to freely enter hole in carbu-
retor throttle lever.'
NOTE:
Accelerator linkage is outlined in de-
tail in Section 6M.
5. Connect accelerator rod at throttle lever.
Service Crankcase Ventilation (Fig. 10}
All engines have either "Positive" or "Closed Positive"
ventilation systems utilizing manifold vacuum to draw
fumes and contaminating vapors into the combustion
chamber where they are burned. Since it affects every
part of the engine, crankcase ventilation is an important
function and should be understood and serviced properly.
In both "Positive" and "Closed Positive" ventilation,
air is drawn through the engine, (through a regulating
valve) into the manifold, drawing' crankcase vapors and
fumes with it to be burned. "Positive" ventilation uses a
vented-meshed cap for clean air intake to the engine,
while . "Closed Positive" ventilation system draws the
clean air from the carburetor air cleaner and has a
nonvented oil filler cap.
1.
Ventilation valve may be checked as outlined under
"Additional Checks and Adjustments".
2.
Inspect for deteriorated or plugged hoses.
3.
Inspect all hose connections.
4.
On closed positive ventilation systems, remove flame
arrestor and wash in solvent then dry with com-
pressed air.
Service Air Injection Reactor System
Inspect air injection reactor system for evidence of
leaks,
deteriorated hoses, cracked air manifolds or tubes
and loose hose clamps. Inspect air injection pump belt
condition and tension. Make all necessary repairs as
outlined in "Section 6T".
Because of the relationship between "Engine Tune Up"
and "Unburned Exhaust Gases", the condition of Engine
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE 6-7
Tune Up should be checked whenever the Air Injection
Reactor System seems to be malfunctioning. Particular
care should be taken in checking items that affect fuel-air
ratio such as the crankcase ventilation system, the car-
buretor and the carburetor air cleaner. Carburetors and
distributors for engines with the Air Injection Reactor
System are designed, particularly, for these engines;
therefore, they must not be interchanged with or replaced
by a carburetor or distributor designed for an engine
without the Air Injection Reactor System.
Choke Adjustment (Fig. 11)
With Remote Choke
1.
Remove air cleaner and check to see that choke
valve and rod move freely.
2.
Disconnect choke r*od at choke lever.
Check choke adjustment as follows:
On all except 275 hp 327 cu. in. engines, hold
choke valve closed and pull rod up against stop. The
top of choke rod end should be 1/2 - 1 rod diameter
4.
5.
above top of hole in choke valve lever.
On 275 hp 327 cu. in. engines, hold choke valve
closed and push rod down against stop on thermostat
bracket. The top of the choke rod should be 1/2 - 1
rod diameter below the top of the hole in the choke
lever.
If necessary, adjust rod length by bending rod at off-
set. (Bend must be such that rod enters choke lever
hole freely and squarely.)
Connect rod at choke lever and install air cleaner.
3.
With Manual
Choke
1.
Remove air cleaner.
2.
Push hand choke knob in to within 1/8" of instrument
panel.
3.
Loosen choke cable at carburetor bracket and adjust
cable through the clip until the choke valve is wide
open.
4.
Tighten cable clamp at carburetor bracket and check
operation of choke valve to ensure full closed and
wide open positions.
INSTRUMENT CHECK-OUT
Instrument Hook Up
Connect vacuum gauge, dwell meter, tachometer and
timing light as recommended by the manufacturer of the
equipment being used.
Check and Adjust Dwell
1.
Start engine then ch^ck ignition dwell.
.2.
If dwell is not within specifications, adjust dwell as
follows:
V8 ENGINES
• With engine running at idle, raise the adjustment
screw window-and insert an Allen wrench in the
socket of the adjusting screw (fig. 12).
• Turn the adjusting screw as required until a dwell
reading of 30° is obtained. A 2° variation is al-
lowable for wear.
• Close access cover fully to prevent the entry of
dirt into the distributor.
NOTE: If a dwell meter is not available, turn
adjusting screw clockwise until engine starts to
misfire, then turn screw one-half turn in the op-
posite direction to complete adjustment.
IN LINE ENGINES
• Remove distributor cap and recheck point setting.
If dwell is still not within specifications check the
distributor as outlined in Section 6Y.
Check Dwell Variation
Slowly accelerate engine to 1500 rpm and note dwell
reading. Return engine to idle and note dwell reading. If
dwell variation exceeds specifications, check for worn
distributor shaft, worn distributor shaft bushing or loose
breaker plate.
WINDOW
"HEX" TYPE
WRENCH
Fig.
12 - Setting Point Dwell (V8)
Fig.
13 - Ignition Timing Marks
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE
6-8
Check
and
Adjust Ignition Timing
(Fig. 13)
1.
Disconnect
the
distributor spark advance hose
and
plug
the
vacuum source opening.
2.
Start engine
and run at
idle speed
(see
tune
up
chart).
3.
Aim
timing light
at
timing
tab.
NOTE:
- The
markings
on the
tabs
are in 2°
increments
(the
greatest number
of
markings
on
the
"A"
side
of the "O"). the "O"
markings
is
TDC
of
#1 cylinder
and all
BTDC settings fall
on
the
"A"
(advance) side
of "O".
4.
Adjust
the
timing
by
loosening
the
distributor clamp
and
,
rotating
the
distributor body
as
required, then
tighten
the
clamp.
5.
Stop engine
and
remove timing light
and
reconnect
the spark advance hose.
Adjust Idle Speed
and
Mixture
(Fig. 14)
(Except when
equipped with
Air
Injection Reactor System)
1.
As a
preliminary adjustment, turn idle mixture
screws lightly
to
seat
and
back
out 2
turns.
CAUTION:
Do not
turn idle mixture screw
tightly against seat
or
damage
may
result.
2.
With engine running
at
operating temperature (choke
wide open) adjust idle speed screw
to
bring idle
speed
to
specified
rpm
(automatic transmission
in
drive, manual transmission
in
neutral).
3.
Adjust idle mixture screw
to
obtain highest steady
idle speed
(1/4
turn
out
from lean roll).
4.
Repeat Steps
2 and 3 as
needed
for
final adjustment.
5.
Shut down
the
engine, remove gauges
and
install
air
cleaner.
Adjust Idle Speed
and
Mixture
(Fig. 14)
(With
Air
Injection Reactor System)
The recommended adjustment procedure
for Air
Injec-
tion Reactor System equipped engines
is as
follows:
1.
As a
preliminary adjustment, turn idle mixture
screws lightly
to
seat
and
than back
out 3
turns.
CAUTION:
Do not
turn idle mixture screw
tightly against seat
or
damage
may
result.
2.
With engine running
at
operating temperature, choke
wide open,
and
parking brake applied, adjust idle
specified idle speed (automatic
"drive"-manual transmission
in
to
in
screw
transmission
"neutral").
;3.
Adjust idle mixture screw (turn
in) to
"lean roll"
position; then turn screw
out 1/4
turn
(1/4
turn rich
from "lean roll").
The
definition
of
"lean roll" point
is
a 20 to 30 rpm
drop
in
engine speed, obtained
by
leaning
the
idle mixture.
4.
Repeat Steps
2 and 3 as
needed
for
final adjustments.
ADDITIONAL CHECKS
AND
ADJUSTMENTS
Testing Crankcase Ventilation Valve
(Fig. 15) 0
1.
Connect tachometer
and
vacuum gauge
as for
idle
speed
and
mixture adjustment.
2.
Set
parking brake, start engine
and
adjust idle speed
and mixture.
3.
Disconnect ventilation hose
at
valve, block opening
of
valve
and
read engine
rpm
change.
4.
A
change
of
less than
50 rpm
indicates
a
plugged
ventilation valve
-
replace
the
valve.
Cylinder Balance Test
(Fig. 16)
It
is
often difficult
to
locate
a
weak cylinder.
A com-
pression test,
for
example, will
not
locate
a
leaky intake
manifold,
a
valve
not
opening properly
due to a
worn
camshaft,
or a
defective spark plug.
With
the
cylinder balance test,
the
power output
of one
cylinder
may be
checked against another, using
a set of
grounding leads. When
the
power output
of
each cylinder
is
not
equal,
the
engine will lose power
and run
roughly.
Perform
a
cylinder balance test
as
follows:
1.
Connect
the
tachometer
and
vacuum gauge.
2.
Start engine
and run at 1500 rpm.
3.
Ground large clip
of
grounding leads
and
connect
in-
dividual leads
to all
spark plugs except
the
pair being
tested.
Divide
the
firing order
in
half
and
arrange
one
half
over
the
other.
The
cylinders
to be
tested together
ap-
pear
one
over
the
other.
L4 Firing Order
V8 Firing Order
1-8-4-3-6-5-7-2
1-6, 8-5, 4-7, 3-2
1-3-4-2
= 1-3
4-2
L6 Firing Order
1-5-3-6-2-4
=
=
1-4. 3-2
1-5-3
6-2-4
1-6, 5-2, 3-4
1-8-4-3
6-5-7-2
4.
Operate engine
on
each pair
of
cylinders
in
turn
and
note engine
rpm and
manifold vacuum
for
each pair.
A variation
of
more than
1
inch
of
vacuum
or 40 rpm
between pairs
of
cylinders being tested indicates that
the cylinders
are off
balance.
Battery
The battery should
be
checked with special testing
equipment
and to the
equipment manufacturers specifica-
tions.
See
Section 6Y
for
complete information
on
battery
tests.
Ignition
The following additional ignition checks
may be
made
with
any of
several pieces
of
equipment available
for un-
covering
the
source
of
engine difficulties.
The
specific
operating instructions
of the
equipment manufacturer
should
be
followed:
Cranking voltage
Ignition switch
Distributor resistance
Secondary resistance
Ignition output
and
secondary leakage
Cranking Voltage
(Fig. 17)
1.
Disconnect coil primary lead
at the
coil negative
terminal
to
prevent engine from firing during
cranking.
2.
Connect voltmeter between primary terminal
of coi|
(resistance wire side)
and
ground.
3.
Operate starting motor.
CHEVROLET CHASSIS SERVICE MANUAL
ENGINE 6-10
Fig.
15 - Crank case Ventilation Valve
a. If voltage is 9 volts or more and cranking speed
is satisfactory, the battery, starter, cables,
starter switch and ignition circuit to coil (by-
passing resistance wire) are in good condition.
b.
If below 9 volts, check circuit until difficulty is
located.
Meter reading below specification—Weak bat-
tery; defective cables, connections, switch or
starter; defective ignition circuit to coil.
Cranking speed below normal--Excessive re-
sistance in cables or starting motor; excessive
mechanical drag in engine.
Uneven cranking speed—Uneven compression,
defective starter or starter drive.
Ignition Switch
With voltmeter connected as described for the Cranking
Voltage Test, turn ignition switch to ON. Voltage should
drop to 5 to 7 volts as current is now passing through
high resistance wire connected between ignition switch
and (+) positive terminal of coil. If battery voltage of
12 volts is obtained, the starter solenoid is by-passing
the high resistance wire connected between ignition
switch and (+) positive terminal of coil, thus the starter
solenoid is not functioning properly to bypass the ignition
resistance wire or the ignition circuit is incorrectly
wired.
Distributor Resistance
Use equipment as directed by manufacturer.
Excessive
(t n ti ft
Fig.
16 - Cylinder Balance Test
Fig.
17 - Testing Cranking Voltage
resistance in primary circuit must be eliminated before
continuing with test procedure.
Secondary Resistance
Use equipment as dire6ted by manufacturer.
• Uniform "normal readings" as specified by manu-
facturer indicate all secondary circuit components
are in good condition.
• If all readings are "below normal," check for cor-
roded coil tower terminal, poorly connected or
broken coil wire, center cap electrode or rotor tip
burned, or an open secondary in coil.
• If readings are "higher than normal" at two or more
plugs adjacent in firing order, cross firing is oc-
curring in distributor cap or between spark plug ca-
bles concerned.
• If meter reads off scale to left, the coil polarity is
reversed. Check for reversed coil primary wires,
wrong coil or reversed vehicle battery connections.
Ignition Output and Secondary Leakage
Use equipment as directed by manufacturer.
• GOOD readings indicate both ignition output and
secondary insulation are good.
• If all readings are BAD or if ignition test calibrator
cannot be adjusted to Set Line, check for high re-
sistance in primary circuit, defective distributor
points, coil or condenser.
e If readings are BAD when certain plug wires are
lifted off, check for cracks or carbon tracks in dis-
tributor cap or defective insulation on those plug
wires being lifted off.
CHEVROLET CHASSIS SERVICE MANUAL