Adjust the speed control to vary the distributor speed between
DISTRIBUTOR TESTS - OFF VEHICLE
400 and 4000 engine rpm. or at the maximum speed of the
The following instructions indicate the general principles to be
engine on which the distributor is used. Erratic or thin faint
followed for testing the distributor.on a tester. The method of testing,
flashes of light preceding the regular flashes as the speed of
however, may vary for machines of different manufacture. For specific
rotation is increased can be due to weak breaker arm spring
instructions refer to the equipment manufacturer's handbook.
tension or binding of the breaker arm on the pivot pin.
Mount the distributor on the tester. Check that the distributor is
Operate the distributor at approximately 2500engine rpm and
free to rotate.
move the protractor scale so that the zero degree mark on the
Make the necessary electrical connections and zero the
scale is opposite one of the neon flashes. The balance of all the
instrument if required.
flashes should come within I degree, plus or minus, evenly
Tighten the drive chuck to the distributor drive shaft securely.
around the protractor scale. A variation larger than 1 degree or
Rotate the drive chuck by hand to make sure the distributor
erratic or wandering flashes may be caused by a worn cam or
shaft turns freely and then tighten the locking screw on the
distributor shaft or a bent distributor shaft.
distributor support arm.
Connect the Synchograph test lead to the primary wire of the
Disconnect and plug the distributor vacuum line.
Turn the test selector switch to the correct cam angle position
Breaker Point Resistance
and operate the distributor at approximately 1000 engine rpm.
Turn the test selector to the position for checking resistance.
Adjust the breaker point gap until the dwell angle is to
specifications. Unplug and connect the distributor vacuum line
Rotate the chuck by hand until the distributor breaker points are
Breaker Plate Wear
The pointer on the cam angle meter should read in the OK zone
A worn breaker plate on the distributor will cause the breaker
of the meter scale. If the meter pointer does not fall in the OK
point gap and contact dwell to change as engine speed and load
zone, there is excessive resistance caused by a faulty contact
conditions are varied.
across the distributor points. a damaged primary lead, or a
Adjust the test set to O degree advance, 0 inches vacuum, and
poorly grounded base plate. A faulty contact across the
100 rpm. Adjust the dwell angle to 26 degrees. Apply vacuum to the
distributor points indicates improper spring tension or burned or
distributor diaphragm and increase it very slowly while observing the
indicated dwell angle. The maximum dwell angle variation should not
exceed 4 degrees when going from zero to maximum vacuum at
Insulation and Leakage
constant rpm. If the dwell angle variation exceeds this limit, there is
Turn the test selector to the cam angle position and rotate the
excessive wear at the stationary subplate pin or the diaphragm rod is
chuck by hand until the distributor breaker contacts are open.
bent or distorted.
The cam angle meter should show a zero reading. If a zero
reading is not obtained, a short circuit to ground exists.
A short could be caused by poor primary wire insulation, a
Distributor Spark Advance Test
shorted condenser or a short between the breaker arm and breaker
The spark advance is checked to determine if the ignition timing
advances in proper relation to engine speed and load.
Check the contact dwell. If the contact dwell is not within
specifications, adjust the breaker points.
Manually check the advance mechanism by turning the rotor in
Check the breaker arm spring tension and adjust it or replace
the direction of distributor rotation and then releasing it. The
the points as necessary.
rotor will return to its original position if the mechanism has
The dual advance distributor has two independently operated
freedom of movement and the springs are in good condition.
spark advance systems. Each system is adjusted separately. Adjust
Make the necessary connections for the stroboscopic timing
the centrifugal advance before adjusting the vacuum advance.
light or sparking protractor. (Refer to equipment manufacturer's
If the correct advance is not indicated at this rpm, stop the distributor
and bend one spring adjustment bracket to change its tension (Figure
6). Bend the adjustment bracket away from the distributor shaft to
Accurate ignition system adjustments are of great importance in
decrease advance (increase spring tension) and toward the shaft to
the proper operation and performance of the engine.
increase advance (decrease spring tension). After the adjustment is
After any adjustment of ignition timing and distributor point dwell,
made, identify the bracket.
check the distributor automatic advance for proper operation.
After an adjustment has been made to one spring, check the
minimum advance point again.
Operate the distributor at the specified rpm to give an advance
just below the maximum. If this advance is not to specifications,
Operate the distributor in the direction of rotation and adjust the
stop the distributor and bend the other spring bracket to give the
speed to the initial rpm setting listed in the specifications. Move
the protractor scale so that one of the flashes lines up with the
Check the advance at all rpm settings listed in the
zero degree mark.
specifications. Operate the distributor both up and down the
Slowly increase the rpm to the setting specified for the first
advance reading listed in the specifications.