Chevrolet Light Duty Truck 1973 Service Manual page 339

Fig. 2—Spark Plug Detail
4. Tighten all ignition system connections.
5. Replace or repair any wires that are frayed, loose
or damaged.
Distributor (Figs. 4 or 5)
1. Check the distributor centrifugal advance mecha­
nism by turning the distributor rotor in a clockwise
direction as far as possible, then releasing the rotor
to see if the springs return it to their retarded
position. If the rotor does not return readily, the
distributor must be disassembled and the cause of
the trouble corrected.
2. Check to see that the vacuum control operates
freely by turning the movable breaker plate
counterclockwise to see if the spring returns to its
retarded position. Any stiffness in the operation of
the vacuum control will affect the ignition timing.
Correct any interference or binding condition
noted.
3. Examine distributor points and clean or replace if
necessary.
• Contact points with an overall gray color and
only slight roughness or pitting need not be
replaced.
• Dirty points should be cleaned with a clean point
file.
Use only a few strokes of a clean, fine-cut contact
file. The file should not be used on other metals and
should not be allowed to become greasy or dirty.
Never use emery cloth or sandpaper to clean contact
points since particles will embed and cause arcing
and rapid burning of points. Do not attempt to
remove all roughness nor dress the point surfaces
down smooth. Merely remove scale or dirt.
• Clean cam lobe with cleaning solvent and rotate
cam lubricator wick 180°.
NOTE: Where prematurely burned or badly
pitted points are encountered, the ignition
system and engine should be checked to
determine the cause of trouble so that it can
be eliminated. Unless the condition causing
point burning or pitting is corrected, new
points will provide no better service than the
old points. Refer to Section
analysis of point burning or pitting.
• Check point alignment (fig.
distributor contact point gap to .019" (new
points) or .016" (used points). Breaker arm
rubbing block must be on high point of lobe
during adjustment.
NOTE: If contact points have been in service,
they should be cleaned with a point file
before adjusting with a feeler gauge.
• Check distributor point spring tension (contact
point pressure) with a spring gauge hooked to
breaker lever at the contact and pull exerted at
90 degrees to the breaker lever. The points
should be closed (cam follower between lobes)
and the reading taken just as the points separate.
If not within limits, replace.
Excessive point pressure will cause excessive wear on
the points, cam and rubbing block. Weak point
pressure permits bouncing or clattering, resulting in
arcing and burning of the points and an ignition
miss at high speed.
4. Install rotor and distributor cap. Press all wires
firmly into cap towers.
SERVICE BATTERY AND BATTERY
CABLES
1. Measure the specific gravity of the electrolyte in
each cell (fig. 7). If it is below 1.230 (corrected to
80°F.) recharge with a slow rate charger, or if
desired, further check battery.
2. Connect a voltmeter across the battery terminals
and measure the terminal voltage of the battery
during cranking (disconnect the coil primary lead at
the negative terminal during this check to prevent
engine from firing). If the terminal voltage is less
than 9.0 volts at room temperature, approximately
20°F., the battery should be further checked.
80°
±
See Section Y for further tests.
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3. Inspect for signs of corrosion on battery, cables and
surrounding area, loose or broken carriers, cracked
or bulged cases, dirt and acid, electrolyte leakage
and low electrolyte level. Fill cells to proper level
With colorless, odorless, drinking water.
The top of the battery should be clean and the
EN G IN E 6-3
Y for an
6
) then, adjust
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LIGHT DUTY TRUCK SERVICE MANUAL