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8
Chapter
l-General Engine Overhaul,
In
spection,
and Repair
regulate
engine operating
temperature
and provide for
a short engine
warm-up
period.
(I) ENGINE OVERHt.'ATS. Usually, engine over·
heating is the
result of
insufficient coolant
supply.
Check
the coolant first. Make
certain
that the
cause of
trouble
is
not anti-freeze
evaporation.
(a)
II
the supply is
low,
check
for leaks in the
cool·
ing
system,
then make the necessary
repairs.
(b) Check
the
water pump belt
for
proper
tension
and adjust it
if
it
is
loose.
(c)
Inspect the
radiator
fins for
obstructions (bugs,
dirt,
etc.). Clean
it if
it
is
clogged.
(d)
Using
a
thermometer in the radiator,
check
the
gauge reading for
accuracy.
NOTE: Inaccurate readings are
someti~nes
caused
by
insufficient clearance between tire Ifetid
c(I!Jting and
Ihe temperature
sending
unit
elemen4 Make repairs
or replacemenl5 as neceuary.
(e)
Check
the thermostat for
proper
operation and
heat range. If it
is
defective
or of
the
wrong
heat
range,
replace it.
Make
sure
the thermostat
IS
correctly
installed.
(f)
Check
the
ignition
timing
and adjust
it if
necessa
ry.
(g) Check
the radiator for proper flow. F lush
it
if
necessary.
(h)
Remove the water pump
and check
for
a
defec-
tive impeller
or a
water
passage obstruction.
Make
repairs or
replacements
as necessary.
(i)
Check the cylinder
head(s)
for water passage
obstructions.
Clean out the passages or replace the
head(s)
if necessary.
(j)
Check the
cylinder
block
for water
passage oJ>.
structions. Clean
out the passages
or
replace the block
if necessary.
(2) ,.;NGINE
FAILS
TO
REACH NORMAL OPER·
ATING TEMPERATURE.
Generally, this is caused
by
the thermostat sticking
or being
o
f
the wrong
heat
range. Check
the thermostat first. If the
engine
still
does
not
reach operating
temperature,
check
the
gauge
and
sending
unit
with
a thermometer installed
in
the radia-
tor. Replace any
defective parts.
2.
TUNE·UP
Regular maintenance
and
inspection
services are
nec-
essary
for proper truck
operation.
In
addition,
to main-
tain
satisfactory
performance,
a
periodic
engine tune-up
should be made.
A
reliable type of engine test equipment
should
be
used to perform the tests
outlined.
in the
checking
pro-
cedures.
As
the checks and tests
ar~
made, make a visual
inspection of the wiring, vacuum 'hoses, cooling system
hoses, heater hoses, etc.
a. Minor
Tune·Up.
Perform the
following
operations in
the
order given,
(I)
INSI,,.;CT
U;NITION
WIRES,
BATTERY
CAIJLES, AND CHECK THE CONDITION
OF
THE
BAT1'1:'.-'R Y.
Inspect all
ignition
wires
for
worn or
damaged
insulation.
Make
sure the wires are
firmly
seated in
the
distriqutor
cap
and that the terminals and
the
terminal
sockets
are free from
corrosion.
Inspect
the battery case for cracks
and leaks.
Make
a battery
capacity
test.
If
unsatisfactory, make a battery
charge test.
If
the charge is
low,
recharge the battery.
Inspect
the battery cable
connections
for corrosion, and
clean them if necessary.
Brush
the
cable connectors with
grease
to retard further
corrosion, then tighten the con-
nectors
securely.
(2) TEST CYLlNDf;R COMPRf;SSION. Be sure the
battery
is good.
Operate
the engine until normal oper-
ating temperature is reached.
Turn
the ignition switch
off.
Remove
all spark
plugs.
Set the thrott le
in the wide
open
position
and
be sure
the
choke
is
wide open.
Install
a compression
gauge in
number 1
cylinder.
Crank
the engine
until
the
gauge
registers
a
maximum
reading and
record the reading.
Note the number of compression strokes
required to
obtain
this reading.
Repeat
the test on each cylinder,
cranking
the
engi
ne
the same number of strokes as
was
required to obtain a maximum reading on
number
1
cylinder.
A
variation of
±
10 pounds from
specified
pressure
is
satisfactory.
However, the
compression o
f
all
cylinders
shou ld
be uniform within 10 pounds.
A
reading of
more than 10 pounds
above
normal indi-
cates ca
r
bon or
lead deposits
in
the cylinder.
A reading of
more than 10
pounds
below normal indi-
cates
leakage at
the head
gasket, rings,
or
va lves.
A
low
even compression
in two
adjacent
cylinders
indicates
a
head gasket
leak. This
s
hould
be checked
before co
ndeming the rings
or valves.
T
o
determine whether the
rin
gs
or
the
valves
are at
fault, put a
tablespoon
of heavy oi
l
on
the piston, and
repeat
the
compressio
n
test.
The oi
l
will temporarily
sea
l
lea
kage past the rings. If the
same
reading
is
ob-
tained, the
rings
are satisfactory,
but the va lves are
leaking.
If
the
com
pression has increased
10
pounds or
more over
the
original reading,
it indi
ca
tes there is leak·
age
past
the rings.
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