ST_330_72_1972_Chevrolet_Truck_Chassis_Service_Manual_10_to_30

ENGINE 6-10

V8 Firing O rder 3. O perate starting m otor.
1-8-4-3-6-5-7-2 = 1-8-4-3 = 1-6, 8-5, 4-7, 3-2 a. If voltage is 9 volts or m ore and cranking speed
6-5-7-2 is satisfactory, the battery, sta rte r, cables,
s ta rte r switch and ignition c irc u it to coil (by­
4. O perate engine on each p air of cylinders in turn and passing resistance wire) are in good condition.
note engine rpm and manif6ld vacuum for each pair. b. If below 9 volts, check circuit until difficulty is
A variation of m ore than 1 inch of vacuum or 40 rpm located.
between p a irs of cylinders being tested indicates that M eter reading below specification-Weak bat­
the cylinders are off balance. tery; defective cables, connections, switch or
starter; defective ignition circuit to coil.
Battery Cranking speed below norm al—Excessive r e ­
sistance in cables or starting motor; excessive
The battery should be checked with special testing mechanical drag in engine.
equipment and to the equipment m anufacturers specifi­ Uneven cranking speed—Uneven com pression,
cations. See Section 6Y for complete inform ation on defective sta rte r to s ta rte r drive.
battery tests.
Ignition Switch
Ignition
With voltm eter connected as described for the Cranking
The following additional ignition checks may be made Voltage T est, turn ignition switch to ON. Voltage should
with any of several pieces of equipment available for drop to 5 to 7 volts a s c u rren t is now passing through
uncovering the source of engine difficulties. The specific high resistance wire connected between ignition switch
operating instructions of the equipment m anufacturer and (+) positive term inal of coil. If b attery voltage of
should be followed. 12 volts is obtained, the s ta rte r solenoid is by-passing
the high resistance wire connected between ignition
• Cranking voltage switch and (+) positive term inal of coil, thus the s ta rte r
• Ignition switch solenoid is not functioning properly to by-pass the igni­
• Distributor resistance tion resistance wire or the ignition circuit is incorrectly
• Secondary resistance w ired.
• Ignition output and secondary leakage
NOTE: The voltage drop (12 to 5-7 volts) will
Cranking Voltage (Fig. 19) only take place when the points a re closed. If
the points are open, the path through the re s is t­
1. Disconnect coil p rim a ry lead at the coil negative ance wire will not be completed.
term inal to prevent engine from firing during
cranking. Distributor Resistance

2. Connect voltm eter between prim ary term in al of coil Use equipment as directed by m anufacturer. Excessive
resistance in prim ary circuit m ust be eliminated before
(resistance wire side) and ground. continuing with test procedure.

Fig. 19—Testing Cranking V o ltage Fig. 20—Cooling System Pressure Check

10-30 CHEVROLET TRUCK SERVICE MANUAL

Secondary Resistance ENGINE 6-11

Use equipment as directed by m anufacturer. 2. Adjust valves on L-6 engines as follows:
• Uniform “ normal readings’' as specified by manu­ a. Mark distributor housing, with chalk, at number
one and number six positions (plug wire) then
facturer indicate all secondary circuit components disconnect plug w ires at spark plugs and coil and
are in good condition. remove distributor cap and plug wire assem bly
• If all readings a re “ below n o rm a l," check for co r­ (if not previously done).
roded coil tower term inal, poorly connected or b. Crank engine until distributor rotor points to
broken coil w ire, center cap electrode or rotor tip number one cylinder position and breaker points
burned, or an open secondary in coil. are open. The following valves can be adjusted
• If readings a re “ higher than norm al’’ at two or m ore with engine in number one firing position:
plugs adjacent in firing o rd e r, c ro ss firing is o ccur­ L6 Engine - Number one cylinder-E xhaust and
ring in distributor cap or between spark plug cables Intake
concerned. Number two cylinder-Intake
• If m eter reads off scale to left, the coil polarity is Number three cylinder-Exhaust
reversed,, Check for reversed coil prim ary w ires, Number four cylinder-Intake
wrong coil or reversed vehicle battery connections. Number five cylinder-Exhaust
c. Back out adjusting nut until lash is felt at the push
Ignition Output and Secondary Leakage rod then turn in adjusting nut until all lash is
removed. This can be determined by checking
Use equipment as directed by m anufacturer. push rod end play while turning adjusting nut
• GOOD readings indicate both ignition output and (fig. 21). When play has been removed, turn ad­
justing nut in one full additional turn (to center
secondary insulation are good. lifter plunger).
• If all readings a re BAD o r if ignition te s t c alib rato r d. Crank engine until distributor ro to r points to
number six position and breaker points are open.
cannot be adjusted to Set Line, check for high re s is ­ The following valves can be adjusted with engine
tance in prim ary circuit, defective distributor points, in number six firing position:
coil or condenser. L6 Engine - Number two cylinder-E xhaust
• If readings a re BAD when c ertain plug w ires are Number three cylinder-Intake
lifted off, check for cracks or carbon tracks in d is­ Number four cylinder-Exhaust
trib u to r cap or defective insulation on those plug Number five cylinder-Intake
w ires being lifted off. Number six cylinder-Intake and
Exhaust
Carburetor
3. Adjust valves on V-8 engines using the following
R efer to Section 6M to p erfo rm adjustm ents such as procedures:
float level, pump rod and vacuum break. a. Crank engine until m ark on torsional dam per
lines up with center or “ 0” m ark on the tim ing
Fuel Pump
Fig. 21—V a lv e Adjustment (L6 Engine)
If the owner has complained of poor high speed p e r­
form ance, the fuel pump may be at fault. Too low a
pump p ressu re or volume will cause a high speed “ m iss’’
because of lack of fuel delivered to the carburetor,
while too high a p ressu re will cause carburetor flooding.
Check fuel pump a s outlined in Section 6M.

Cooling System

The following test may be perform ed with p ressu re
testing equipment available com m ercially for this pu r­
pose. T his te s t provides an excellent m eans of detecting
internal or external leaks within the cooling system .

1. Remove ra d ia to r cap.
2. Apply a te s t p re s s u re of 3 pounds higher than the

ra d ia to r cap (fig. 21), i.e. 18 pounds for a 15 pound
cap.
3. If the p re s s u re will not hold, th ere is either an
internal or external leak in the system .

Cylinder Head Torque and V a lv e Adjustment

Retorquing the cylinder head bolts is not necessary
unless a gasket has been replaced, or a leak is suspected.
Valve lash m ust always be adjusted after the head has
been torqued.

Hydraulic V alve Adjustment

1. Remove ro ck er arm cover(s) and gasket(s).

CAUTION: Do not pry ro ck er arm cover loose.
Gaskets adhering to cylinder head and rocker
arm cover may be sh eared by bumping end of
ro ck er arm cover re a rw a rd with palm of hand
or a rubber mallet.

10-30 CHEVROLET TRUCK SERVICE MANUAL

ENGINE 6-12 Fig. 22—Valve Adjustment (V8 Engine)

tab and the engine is in the number 1 firing posi­ 4. Clean gasket surfaces on cylinder head(s) and rocker
tion. This may be determ ined by placing fingers arm cover(s) with degreaser, then install rocker
on the num ber 1 cylinder valve as the m ark on arm cover(s), using new gasket(s), and torque bolts
to specifications.
the dam per com es near the “0” m ark on the
5. Install d istrib u to r cap and spark plug w ire assem bly.
front cover. If the valves are not moving, the en­ 6. Install ro cker a rm cover as outlined.
gine is in the number 1 firing position. If the 7. Adjust carburetor idle speed.
valves move as the m ark comes up to the timing
tab, the engine is in number 6 firing position and
crankshaft should be rotated one m ore revolution
to reach the number 1 position.
b. Valve adjustm ent is made by backing off the ad­
justing nut (ro ck er a rm stud nut) until th ere is
play in the push rod and then tighten nut to just
remove all push rod to rocker arm clearance.
This may be determ ined by rotating push rod with
fingers as the nut is tightened (fig. 22). When
push rod does not readily move in relation to the
rocker arm , the clearance has been eliminated.
The adjusting nut should then be tightened an
additional 1 turn to place the hydraulic lifter
plunger in the cen ter of its trav el. No other ad­
justment is required.
c. With the engine in the number 1 firing position as
determ ined above, the following valves may be
adjusted.

Exhaust - 1, 3, 4, 8
Intake - 1, 2, 5, 7

d. C rank the engine one revolution until the pointer

“0” m ark and torsio n al dam per m ark are again

in alignment. This is number 6 firing position.
With the engine in this position the following valve
may be adjusted.

Exhaust - 2, 5, 6, 7
Intake - 3, 4, 6, 8

10-30 CHEVROLET TRUCK SERVICE MANUAL

ENGINE 6-13

ENGINE MECHANICAL
IN-LINE ENGINES

INDEX

Page Page

G en eral D e s c r i p t i o n ................................................................................. ...0.13 O il P u m p ............................................................ ................................................. 6-18
C om ponent R e p la c e m e n t and A d ju s tm e n t....................................... ...6-13 R e m o v a l .......................................................................................................... 6-18
I n s t a l l a t i o n ................................................................................................... 6-18
E ngine A s s e m b l y .................................................................................... ...6-13 6-19
R e m o v a l ................................................................................................. ...6-13 O il S e a l (R e a r M a in ) ..................................................................................... 6-19
I n s t a l l a t i o n ....................................„ ................................................... ...6-15 R e p l a c e m e n t ............................................................................................... 6-19
6-19
M anifold A s s e m b l y ....................................................................................6-15 T o r s io n a l D a m p e r ........................................................................................ 6-19
R e m o v a l ................................................................................................. ...6-15 R e m o v a l .......................................................................................................... 6-20
I n s t a l l a t i o n ..............................................................................................6-16 I n s t a l l a t i o n ................................................................................................... 6-20
6-20
R o ck er A rm C o v e r ....................................................................................6-16 C r a n k c a s e F r o n t C o v e r .............................................................................. 6-21
R e m o v a l ................................................................................................. ...6-16 R e m o v a l .......................................................................................................... 6-21
I n s t a l l a t i o n ..............................................................................................6-16 I n s t a l l a t i o n ................................................................................................... 6-21
6-21
V a lv e M e c h a n is m .................................................................................... ...6-16 O il S e a l (F r o n t C o v e r ) ................................................................................. 6-22
R e m o v a l ................................................................................................. ...6-16 R e p l a c e m e n t ................................................................................................ 6-22
In sta lla tio n and A d ju s tm e n t.......................................................... ... 6-16 6-23
C a m s h a f t .............................................................................................................. 6-23
V a lv e L i f t e r s .............................................................................................. 6-17 M e a s u r in g L o b e L i f t .............................................................................. 6-23
L o c a tin g N o is y L i f t e r s ................ ................................................... ... 6-17 R e m o v a l .......................................................................................................... 6-23
R e m o v a l ................................................................................................. ... 6-17 I n s t a l l a t i o n ................................................................................................... 6-23
I n s t a l l a t i o n .............................................................................................. 6-17 6-24
T im in g G e a r s ................................................................................................... 6-24
V a lv e Stem O il Seal a n d /o r V a lv e S p r i n g .................................... 6-17 R e p l a c e m e n t ............................................................................................... 6-24
R e p l a c e m e n t ....................................................................................... ... 6-17 6-24
F ly w h e e l ..............................................................................................................
C ylin d er H ead A s s e m b lie s . .............................................................. ... 6-18 R e m o v a l ..........................................................................................................
R e m o v a l ................................................................................................. ... 6-18 I n s t a l l a t i o n ...................................................................................................
I n s t a l l a t i o n .......................................................................................... ... 6-18
E n g in e M o u n t s ...................................................................................................
O il P a n ...........................................................................................................6-18 C hecking E ngine M o u n t s ................................................................ ...
R e m o v a l ................................................................................................. ... 6-18 R eplacem en t (F r o n t).....................................................................................
I n s t a l l a t i o n .............................................................................................. 6-18 R eplacem en t ( R e a r ) .....................................................................................

GENERAL DESCRIPTION

The In-L ine engines covered in this section are the 250 Because of the interchangeability and sim ila rity of
and 292 cu. in. L6 engines used in 10-30 S eries truck many engine sub-assem blies and parts, regardless of
which truck vehicle they are used in, typical illustrations
vehicles (fig. 1L). and procedures are used (except where specific illus­
This section covers the rem oval and installation of en­ trations or procedures are necessary to clarify the
operation). Although illustrations showing bench opera­
gine assem blies, the rem oval, installation and adjustment tions a re used, m ost single operations, when not p a rt of a
of som e su b -assem b lies and replacem ent of some com­ general overhaul, should be perform ed (if practical) with
ponents. For service to all components and sub- the engine in the vehicle.
assem b lies (after rem oval) and r e m o v a l of some
sub-assem blies, re fe r to Section 6 of the Chassis Over­

haul Manual.

COMPONENT REPLACEMENT AND ADJUSTMENT

Engine Assembly 4. Disconnect w ires at:
• Starter Solenoid.
Removal • Delcotron.
• Tem perature Switch.
1. Disconnect b attery cables and drain cooling system . • Oil P re s s u re Switch.
2. Remove the a ir cleaner. • Coil.
3. P erfo rm the following p relim in ary operations. • CEC Solenoid.

ON CS 10-20-30, KS 10-20 SERIES: 5. Disconnect:
• Remove the hood as outlined in Section 11, • A ccelerator linkage at manifold bellcrank.
• Remove the radiator and shroud as outlined in • Fuel line (from tank) at fuel pump.
• Heater hoses at engine connection.
Section 13. • Oil p re ssu re gauge line (if so equipped).
• Vacuum lines at engine (as required)
ON PS 10-20-30 SERIES: • Power steering pump at engine bracket and lay
• Remove the engine box and hood as outlined in
aside (if so equipped).
Section 11. • Ground straps at engine.
• Remove the battery. • Exhaust pipe at manifold.
• Remove the radiator and shroud as outlined in

Section 13.

10-30 CHEVROLET TRUCK SERVICE MANUAL