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ELECTRICAL SYSTEMS
IGNITION SYSTEM
10-65
TIMING MARK
Figure 10-78-lgnition Timing Marks-Series 40-50
b. Ignition Timing
Correct ignition timing exists when the tim-
ing mark on flywheel is in line with the index
mark on flywheel housing at instant that num-
ber one spark plug fires. It is desirable to have
the index mark at the leading edge of timing
mark; however, any position within the yellow
band will give proper performance and econ-
omy.
Ignition timing in advance of the specified
setting may cause roughness in engine opera-
tion, even though high octane fuel is used.
With some fuels, and the specified ignition
timing, a very light "ping" or "spark knock"
may occur with part throttle on a hard pull, or
during acceleration between 10 and 20 MPH
with wide open throttle. These operating condi-
tions are normal and no attempt should be
made to eliminate such detonation by retarding
the ignition timing. If detonation is heavy,
however, the timing should be retarded. If it is
necessary to retard the timing beyond the yel-
low band of timing mark in order to eliminate
heavy detonation, reduced performance and
economy must be
expected.
A change to higher
octane fuel should be made, rather than retard
the timing beyond the specified setting.
c. Se"ing Timing with Synchroscope
Ignition timing should be checked with a syn-
chroscope or power timing light because this
shows the actual timing with engine running.
NOTE: Contact point opening must be within
specified limits before setting ignition timing
(par. 10-45).
1. Remove timing hole cover. Connect syn-
chroscope or power timing light to No.1 spark
plug wire at the plug or the distributor cap,
in accordance with instructions of instrument
manufacturer.
2. Start engine and set it to idle at a speed
not to exceed 350 RPM so that centrifugal and
vacuum advance mechanisms are not in opera-
tion. This is absolutely necessary to insure cor-
rect timing.
3. Direct the beam of timing light into the
timing hole so that the t
iming
mark on flywheel
and index mark on flywheel housing can be ob-
served.
See figure 10-78. The index mark must
fall within the yellow band of the ignition tim-
ing mark for proper timing.
4. If necessary, loosen attaching bolts and
turn the distributor housing very slowly in di-
rection required to make the index mark fall
within the yellow band of the ignition timing
mark and as near leading edge of band as pos-
sible. Tighten distributor attaching screws and
recheck timing.
5. Install timing hole cover and spark plug
cover.
Figure 10-79-Checking Ignition Timing wi
th
Spark
d. Setting Timing without Synchroscope
If
synchroscope or power timing light is not
available, ignition timing may be set by the fol-
lowing procedure. NOTE: Contact point open-
ing must be within specified limits before set-
ting ignition timing (par. 10-45).
1. Remove timing hole cover and distribu-
tor cap. With ignition turned off, turn engine
until distributor rotor is approximately under
No.1 terminal in distributor
cap.
2. Turn flywheel in forward direction until
the index mark on flywheel housing falls within
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