Chevrolet Light Duty Truck 1973, Service Manual

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EN G IN E 6 -1 3
occurring in distributor cap or between spark plug
cables concerned.
• If meter reads off scale to left, the coil polarity is
reversed. Check for reversed coil primary wires,
wrong coil or reversed vehicle battery connections.
Ignition Output and Secondary Leakage
Use equipment as directed by manufacturer.
• GOOD readings indicate both ignition output and
secondary insulation are good.
• If all readings are BAD or if ignition test calibrator
cannot be adjusted to Set Line, check for high
resistance in primary circuit, defective distributor
points, coil or condenser.
• If readings are BAD when certain plug wires are
lifted off, check for cracks or carbon tracks in
distributor cap or defective insulation on those plug
wires being lifted off.
CARBURETOR
Refer to Section
6
M to perform adjustments such as float
level, pump rod and vacuum break.
FUEL PUMP
If the owner has complained of poor high speed
performance, the fuel pump may be at fault. Too low a
pump pressure or volume will cause a high speed “miss”
because of lack of fuel delivered to the carburetor, while
too high a pressure will cause carburetor flooding. Check
fuel pump as outlined in Section
6
M.
COOLING SYSTEM
The following test may be performed with pressure
testing equipment available commercially for this
purpose. This test provides an excellent means of
detecting internal or external leaks within the cooling
system.
1. Remove radiator cap.
2. Apply a test pressure of 3 pounds higher than the
radiator cap (fig. 20), i.e. 18 pounds for a 15 pound
cap.
3. If the pressure will not hold, there is either an
internal or external leak in the system.
CYLINDER HEAD TORQUE AND
VALVE ADJUSTMENT
Retorquing the cylinder head bolts is not necessary
unless a gasket has been replaced, or a leak is suspected.
Valve lash must always be adjusted after the head has
been torqued.
Valve Adjustment
1. Remove rocker arm cover(s) and gasket(s).
CAUTION:
Do not pry rocker arm cover loose.
Gaskets adhering to cylinder head and rocker
arm cover may be sheared by bumping end of
rocker arm cover rearward with palm of hand
or a rubber mallet.
2. Adjust valves on L
-6
engines as follows:
a. Mark distributor housing, with chalk, at number
one and number six positions (plug wire) then
disconnect plug wires at spark plugs and coil
and remove distributor cap and plug wire
assembly (if not previously done).
b. Crank engine until distributor rotor points to
number one cylinder position and breaker
points are open. The following valves can be
adjusted with engine in number one firing
position:
Number one cylinder-Exhaust and Intake
Number two cylinder-Intake
Number three cylinder-Exhaust
Number four cylinder-Intake
Number five cylinder-Exhaust
c. Back out adjusting nut until lash is felt at the
push rod then turn in adjusting nut until all lash
is removed. This can be determined by checking
push rod end play while turning adjusting nut
(fig.
21
). When play Has been removed, turn
adjusting nut in one full additional turn (to
center lifter plunger).
d. Crank engine until distributor rotor points to
number six position and breaker points are
open.
The following valves can be adjusted with engine in
number six firing position:
Number two cylinder-Exhaust
Number three cylinder-Intake ' -
Number four cylinder-Exhaust
Number five cylinder-Intake
Number six cylinder-Intake and Exhaust
3. Adjust valves on V
-8
engines using the following
procedures:
a. Crank engine until mark on torsional damper
lines up with center or “
0
” mark on the timing
tab and the engine is in the number
1
firing
position. This may be determined by placing
fingers on the number
1
cylinder valve as the
mark on the damper comes near the “
0
” mark
on the front cover. If the valves are not moving,
the engine is in the number 1 firing position. If
the valves move as the mark comes up to the
timing tab, the engine is in number
6
firing
position and crankshaft should be rotated one
more revolution to reach the number
1
position.
b. Valve adjustment is made by backing off the
adjusting nut (rocker arm stud nut) until there is
play in the push rod and then tighten nut to just
remove all push rod to rocker arm clearance.
This may be determined by rotating push rod
LIGHT DUTY TRUCK SERVICE MANUAL