Chevrolet 10 Series 1968, Руководство по обслуживанию

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ENGINE 6-9
sistance in cables or starting motor; excessive
mechanical drag in engine.
Uneven cranking speed—Uneven compression,
defective starter or starter drive.
Ignition Sw itch
With voltmeter connected as described for the Cranking
Voltage Test, turn ignition switch to ON. Voltage should
drop to 5 to 7 volts as current is now passing through
high resistance wire connected between ignition switch
and (+) positive terminal of coil. If battery voltage of
12 volts is obtained, the starter solenoid is by-passing
the high resistance wire connected between ignition
switch and (+) positive terminal of coil, thus the starter
solenoid is not functioning properly to by-pass the igni­
tion resistance wire or the ignition circuit is incorrectly
wired.
D istributor Resistance
Use equipment as directed by manufacturer. Excessive
resistance in primary circuit must be eliminated before
continuing with test procedure.
S e co n d a ry Resistance
Use equipment as directed by manufacturer.
• Uniform “ normal readings” as specified by manu­
facturer indicate all secondary circuit components
are in good condition.
• If all readings are “ below normal,” check for cor­
roded coil tower terminal, poorly connected or
broken coil wire, center cap electrode or rotor tip
burned, or an open secondary in coil.
• If readings are “ higher than normal” at two or more
plugs adjacent in firing order, cross firing is occur­
ring 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.
F ig . 17—C o o lin g System Pressure Test
F ig . 18—O il D eflector C lip s Installed
Ignition O utput and Se co n d a ry Lea ka g e
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 resis­
tance 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 dis­
tributor cap or defective insulation on those plug
wires being lifted off.
Carburetor
Refer to Section 6M to perform adjustments such as
idle vent, float level, pump rod and secondary valve.
Fuel Pump
If the owner has complained of poor high speed per­
formance, 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 6M.
Cooling System
The following test may be performed with pressure
testing equipment available commercially for this pur­
pose. 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. 17), 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 V alve 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.
Before adjusting the valve lash, it is extremely im­
portant that the engine be thoroughly warmed up to
CHEVROLET TRUCK SERVICE MANUAL