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 TM 9-4910-749-10
1-6. DISTRIBUTOR-MECHANICAL WEAR TEST
RESULTS:
Good-Points are in good condition
Bad-Points
are
bad.
Replace.
a. Excessive distributor mechanical wear causes
NOTE
inaccurate timing and abnormal spark advance, re-
sulting in poor engine performance.
If the meter reads in the bad range, the
b. To perform the Mechanical Wear Test for
points may be open. Momentarily crank
Distributor:
the engine (without starting) and re-check.
1-5. DWELL TEST
(1) Turn the test selector to the DWELL posi-
tion (See Figure 4).
a. If the point gap is not properly adjusted, the
(2) Briefly increase engine RPM to approxi-
meter will show:
mately 1500, while observing the meter and note
the change in dwell from the value at idle.
(1) Low Dwell, which can be the cause of poor
ignition performance.
NOTE
(2) High Dwell, which can cause excessive
Some distributors have off-center pivoting
burning of the breaker points.
breaker-plates which will cause dwell
changes in excess of 3. This is normal for
b. See your vehicle manual for the correct dwell
this type of distributor. See your vehicle
for your vehicle.
manual.
c. To perform the dwell test:
RESULTS:
Change within 3-Normal
Change more than 3-Worn out
(1) Turn the test selector to the DWELL
distributor, cam, or bushings. Re-
position (See Figure 4).
place or repair as needed.
(2) Turn the cylinder selector to the appro-
1-7. RPM/lDLE SPEED TEST
priate position for your engine.
a. High idle speed causes excessive brake wear,
(3) Start engine, let idle while observing the
while
low
idle
speed
causes
engine
stalling
and
meter.
r o u g h n e s s . Refer to your vehicle manual for correct
idle speed.
b. To perform the idle speed test do the follow-
ing:
(1) Turn the test selector switch to the LOW
RPM position (See Figure 5).
(2) On automatic transmission vehicles, place
s h i f t selector in the correct position as specified by
the auto manufacturers.
POSITION
NOTE
If your distributor is equipped with dual
points, refer to your vehicle manual for
proper
adjustment
testing
and
instructions.
RESULTS: Low-Point gap too wide. Reset.
Normal-Point gap properly adjusted.
ANCE TESTS
High-Point gap too small. Reset.
1-2
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