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IGNITION SYSTEM
8-5 1
the black indicates a normal distributor primary cir-
cuit.
If the reading is outside the black bar, high resist-
ance is present in the distributor primary circuit.
(4)
Remove the test lead from the distributor ter-
minal of the coil and connect to the following points:
(a) Distributor primary terminal (outside)
(b)
Distributor primary terminal (inside)
(c) Contact terminal bracket (insulated bracket).
(d)
Ground side of the contacts.
(e) Distributor housing.
(5)
Repeat the test at each connection until a no-
ticeable change occurs in the meter reading. If a poor
connection or faulty lead is indicated, clean, tighten
or replace
as
necessary and repeat test (3).
If faulty contacts are indicated, remove the distrib-
utor for complete inspection, service, testing and
calibration.
IDLE RPM TEST
The engine idle rpm setting should be tested and
recorded as it is when the vehicle is first brought
into the shop for testing. This will assist in diagnos-
ing complaints of engine stalling, creeping and hard
shifting on vehicles equipped with automatic trans-
missions.
Test procedures are as follows:
(1) Turn the Selector Switch to the CALIBRATE
position and adjust the Dwell Calibrator until the
Dwell Meter reads on the SET line (test leads sepa-
rated).
(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
8
LOBE posi-
tion.
(4)
Turn the tachometer rpm switch to the 1000
rpm position.
(5) With the engine at normal operating tempera-
ture (off fast idle), momentarily open the throttle and
release 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
carburetor idle speed to specifications. See "Fuel Sys-
tem" specifications.
DISTRIBUTOR CONTACT DWELL
The degrees of distributor dwell are the degrees of
rotation through which the contacts remain closed.
This is also commonly referred to as "dwell angle" or
"cam angle."
The correct distributor point dwell i s essential for
good ignition performance and contact point life.
Test procedures are as follows:
(1) Connect the Tach-Dwell red lead to the distrib-
utor terminal of coil and black lead to a good ground.
(2)
Turn the Selector Switch to the
8
LOBE posi-
(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 contact arm may be indicated.
tion.
DUAL CONTACTS
Block one set of contacts with a clean insulator and
adjust the opposite set of contacts to specifications
using the dwell meter.
NOTE: Loosen the stationary contact lock screw
just enough, so that the stationary contact can be
moved with a slight drag; otherwise it will
be diR-
cult to set the contacts accurately.
When the one set of contacts has been adjusted for
the correct clearance, tighten the stationary contact
lock screw.
Block the adjusted set of contacts with an insulator
and adjust the remaining set of contacts in the same
manner
as
the first set. Remove the insulator and re-
check tightness of the stationary contact lock screw.
If the contacts have been properly adjusted, the
dwell should be as specified for two contact sets.
DWELL VARIATION
This test indicates the mechanical condition of the
distributor. Excessive wear in distributor mechanical
parts cause dwell variations which will affect ignition
timing.
Test procedures are as follows:
(1) With the engine at idle speed, the vacuum hose
disconnected, and with the test leads connected
as
in
"Contact Dwell Test," turn the Tachometer rpm
Switch to the
5,000
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 contact plate bearing and pivot pin is indicated.
Remove the distributor for complete inspection and
testing on a distributor tester.
NOTE: Dwell variation at speeds above
1500
rpm
does not necessarily indicate distributor wear.
Dwell and gap of the contacts must both be within
their specified limits at the same time.
If
this can-
not be accomplished, it is probable that the wrong
contacts are installed or the rubbing block or cam
lobes are badly worn
or
movable contact
is
dis-
torted.
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