Advertisement
IGNITION SYSTEM
8-43
position and adjust Dwell Calibrator
until the Dwell
Meter reads on the SET line (test leads separated).
(2)
Connect the red lead of the test unit to the dis-
tributor primary terminal at the coil and the black
lead to a good ground.
(3)
Turn the Selector Switch to the
6
LOBE posi-
tion.
(4)
Turn the tachometer rpm switch to the 1000
rpm position.
(5) With engine at normal operating temperature
(off fast idle), momentarily open the throttle and re-
lease to make sure there is no bind in the linkage
and that the idle speed screw is against its stop.
(6)
Note engine rpm on 1000 rpm scale and adjust
the carburetor idle speed to specifications shown in
Fuel System "Specifications."
DISTRIBUTOR CONTACT DWELL
The degrees of distributor dwell are the degrees of
rotation through which the breaker contacts remain
closed. This is also commonly referred to as "dwell
angle" or "cam angle."
Correct distributor contact dwell is essential for
good ignition performance and contact life.
Test procedures are as follows:
(1)
Connect the Tach-Dwell red lead to the dis-
tributor terminal of coil and black lead to a good
ground.
(2)
Turn the Selector Switch to the
6
LOBE posi-
tion.
(3)
Start the engine and operate at idle speed.
(4)
Observe the dwell meter reading. If the dwell
reading is within "Specifications," the contact gap,
cam rubbing block and contact arm are all in satis-
factory condition.
If the dwell reading is not within specifications, in-
correct contact gap, worn cam, worn rubbing block
or distorted movable contact arm may be indicated.
DWELL VARIATION
This test indicates the mechanical condition of the
distributor. Excessive wear in distributor mechani-
cal parts cause dwell variations which will affect ig-
nition timing.
Test procedures are as follows:
(1) With the engine at idle speed, vacuum hose dis-
connected, and with the test leads connected as in the
contact Dwell Test, turn the Tachometer rpm Switch
to the 5000 rpm position.
(2) Slowly increase the engine speed to 1500 rpm,
then slowly reduce to idle speed while observing the
dwell meter reading.
If the dwell reading varies more than
2
degrees
from initial reading between idle speed and 1500
rpm, probable wear in the distributor shaft, bushings
or breaker plate is indicated. Remove distributor for
complete inspection and testing on a distributor
test-
er.
Dwell variation at speed above
1500
rpm does not
necessarily indicate distributor wear.
IMPORTANT: Dwell and gap of the contacts must
both be within their specified limits at the same
time.
If
this cannot be accomplished, it is probable
that wrong contacts are installed, the rubbing
block
or cam lobes are badly worn or the movable con-
tact arm is distorted.
IGNITION TIMING
To obtain maximum engine performance, the dis-
tributor must be correctly positioned on the engine
to give proper ignition timing.
The ignition timing test will indicate the timing of
the spark at NO. 1 cylinder at idle (only).
Test procedures are as follows:
(1) Disconnect the vacuum hose at the distributor.
(2)
Connect the secondary lead of the Power Tim-
ing Light to NO.
1
spark plug, the red primary lead
to
the positive terminal of the battery and the black
primary lead to the negative battery terminal.
Do not puncture the wires, boots or nipples with
test probes. Always urn adapters. Puncturing spark
plug wires with
a
probe will damage the wires. The
probe can separate the conductor and cause high
resistance. In addition breaking the rubber insula-
tion may permit secondary current to arc to
ground.
(3)
Start the engine and set idle to "Specifica-
tions" (transmission in neutral).
(4)
Use a timing light taobserve the position of the
timing mark on the crankshaft damper and check
against specifications.
(5) Loosen the distributor hold-down arm screw and
rotate the distributor housing so that crankshaft
damper mark aligns with the specified BTC mark on
timing plate. Refer to "Specifications." (Moving the
distributor housing counter-clockwise advances the
ignition timing and clockwise retards the timing.)
(6)
Tighten the distributor hold-down arm screw
after timing has been set and recheck timing adjust-
ment with a Power Timing Light.
(7)
When the ignition timing is correct, reconnect
the vacuum hose to the distributor.
DISTRIBUTOR REMOVAL
(1)
Disconnect the vacuum hose at the distributor.
(2)
Disconnect the primary lead wire at the coil.
(3)
Unfasten the distributor cap retaining clips and
lift off the distributor cap.
(4)
Rotate the engine crankshaft until the distrib-
utor rotor is pointing toward the cylinder block,
scribe a mark on block at this point to indicate the
Hide quick links:
Advertisement
