1953 JEEP DJ service

'Jeep'
UNIVERSAL
SERIES SERVICE
MANUAL

Dl Caution:
Oil ports of the rocker arm shaft must
coincide with oil return passages of the rocker

arms.
If they do not,
engine
oil has no return path

from
the cylinder head to the crankcase; in that
case,
engine
oil flows down the valve
stems
and

burns
in the cylinders.
There
is a notch at one end of each rocker arm shaft. When rocker arms
are
properly installed on the shaft, this notch
will

be at front of right rocker arm shaft and at
rear
of left rocker arm shaft. Refer to
Figs.
Dl-25 and

Dl-26.

a.
Position center support on rocker arm shaft;

insert
one shaft assembly attaching bolt through
support and shaft to hold support in position.

b.
Install
center
pair
of rocker arms with notched
faces touching support.
Install
front and
rear
spacer
FIG.
Dl-25—FRONT
OF RIGHT

ROCKER
ARM SHAFT
1—Alignment Notch

FIG.
Dl-26—REAR OF
LEFT
ROCKER
ARM SHAFT 2—Alignment Notch springs and one rocker arm each of front and
rear

rocker
arm pairs on shaft. Be certain that notched
faces of rocker arms are outward.
Install
outer shaft supports on shaft; compress spacer springs
to position supports. Insert one shaft assembly bolt
through each support and shaft to hold supports in
position.

c.
Install
remaining rocker arms of front and
rear

pairs,
each with notched face touching shaft sup­

port.
Install
a spring retaining ring and flat washer at each end of shaft; secure each of
these
with a
new cotter pin.

D1 -61.
Valve Removal

a.
Place cylinder head on clean, smooth surface.

b.
Remove each valve assembly from cylinder
head as follows. Using suitable spring compressor, compress valve spring and remove two valve re­

tainers
from valve stem. Release spring compressor,

and
remove spring retainer and valve spring from
valve stem. Refer to Fig. Dl-27.

Note:
Valve retainers are copper-colored for identi­
fication purposes only.

c.
Withdraw valve from
bottom
of cylinder head.
Valves
should be identified so they can be installed

in
original location.

D1-62.
Cylinder
Head and Valve Cleaning
and
Inspection

a.
Remove carbon from combustion chamber of
cylinder
heads, using care to avoid scratching the head of valve seat surfaces. A
soft
wire brush is
suitable for this purpose.

b.
Clean
carbon and gum
deposits
from valve guide
bores with a standard-size valve guide reamer.

Refer
to Fig. Dl-28.

c.
Clean
valves with a wire
brush.
Inspect valve
faces and
seats
for pits, burned
spots
or other evi­ dence of poor seating.
FIG.
D1 -2 7—REMOVING
VALVE
RETAINERS
1—
Valve
Stem 3—Valve Spring Retainer

2—
Valve
Lock
4—Valve Spring
93

'Jeep*
UNIVERSAL
SERIES
SERVICE
MANUAL

Dl
Dl-65.
Rocker Arm Cover Cleaning
and Inspection

a.
Clean
both rocker arm covers with suitable
cleaning solvent and dry thoroughly.

b.
Inspect each rocker arm cover visually for

scratches,
bends, dents, and tears. Replace cover

if
unserviceable.

Dl-66.
Timing Chain
and
Sprocket Inspection

Inspect
the timing chain and both sprockets for
damage or excessive wear. Replace unserviceable
parts.

Dl-67.
Timing Chain Cover Cleaning and Inspection

a.
Clean
the timing chain cover with suitable clean­
ing solvent and dry with compressed air.

b.
Inspect the cover visually for breaks,
cracks,
and
other damage.
With
a straightedge, check cylinder
block, water pump, and oil pump faces for bends

and
distortion.

c.
Install
oil pump gears in oil pump cavity of
timing gear cover.
With
a straightedge and feeler
gauge,
check gear and clearance. Refer to Fig.

Dl-30.
Clearance
should be
between
.0023"
[0,0584

mm.] and .0058"
[0,1358
mm.]. If it is lower
than
.0018" [0,0457 mm.], inspect thrust surfaces
of cover which touch gears for wear.

d.
Replace the timing chain cover if unserviceable.
FIG.
Dl-30—CHECKING
OIL
PUMP
GEAR

END
CLEARANCE

1—
Feeler
Gauge
2—
Straight
Edge

3—
Pump
Body
4—
Pump
Gears
Dl-63.
Oil Pump Cleaning and
Inspection

a.
Clean
gears with suitable cleaning solvent and

dry
thoroughly. Inspect for wear, scoring, and other damage. Replace either or both gears if unservice­
able.

b.
Remove the oil pressure relief valve cap, spring

and
plunger. Refer to Fig. Dl-31. Oil filter bypass
valve plunger and spring are staked in place and should not be removed. 12719

FIG.
Dl-31—OIL
PUMP
PRESSURE
RELIEF
VALVE

1—
Valve
Cap
2—
Gasket

3—
Spring

4—Valve
5—
Oil
Pump
Cover
c.
Wash valve parts thoroughly. Inspect the relief
valve plunger for wear or scoring.
Check
the spring to see that it is not worn or collapsed. Replace any
relief
valve spring that is questionable. Thoroughly

clean
the screen staked in the cover.

d.
Insert the relief valve plunger into its bore in
the cover. The plunger should have no more clear­ ance than an easy slip fit. If there is any perceptible
sideways movement, the plunger and/or the cover should be replaced.
e.
Check
oil filter bypass valve plunger for
cracks,

nicks,
or warping. The plunger should be flat and free of nicks or scratches.
f.
Lubricate
and install pressure relief valve plung­
er
and spring in bore of oil pump cover.
Install

cap and gasket. Torque cap to 30 to 40 lb-ft. [4,1 a 5,5 kg-m.]. Do not over-tig1 n.

Note:
Pressure relief valve cap has no tapped
hole

for installation of oil pressure switch.

H1
-69.
Crankshaft Vibration
Damper
Inspection

Inspect
the crankshaft vibration damper for
cracked,
broken, distorted, or otherwise damaged
condition. If damaged, replace.

Dl-70.
Crankshaft Pulley Inspection

Inspect
the crankshaft pulley for damage or exces­
sive wear. Replace if visibly worn or damaged.

Dl-71.
ENGINE REASSEMBLY

The
engine
assembly procedure in the following
paragraphs
is given in the sequence to be followed
when the
engine
is being completely overhauled.
Individual
inspection,
repair,
and fitting operations
previously covered in detail are made throughout
the assembly procedure. The assembly procedure
does
not cover accessories. If a new cylinder block
fitted with pistons is used, many of the operations

will
not be required.

Mount
the cylinder block in an
engine
repair stand.
If
an
engine
stand is not available, perform the
following assembly operation in a manner designed to protect personnel against an accident, and the
engine
and its parts against damage. 95

'Jeep'
UNIVERSAL
SERIES SERVICE
MANUAL

Dl
size have
been
selected. If necessary, check or
select

connecting rod bearings as described in Par. Dl-49.

Note:
When a piston and connecting rod assembly
is properly installed, the oil spurt
hole
in the con­ necting rod
will
face the camshaft. The rib on the

edge
of the bearing cap
will
be on the same side
as the conical
boss
on the connecting rod web;
these
marks (rib and boss)
will
be toward the other
connecting rod on the same crankpin. The notch
on the piston
will
face the front of the
engine.

a.
Be certain that cylinder bores, pistons, connect­
ing rod bearings and crankshaft journals are absolutely clean. Coat all bearing surfaces with

engine
oil.
b. Before installing a piston and connecting rod as­
sembly into its bore, rotate the crankshaft so that
the corresponding crankpin is moved downward, away from the cylinder bore.
c. Remove bearing cap from connecting rod. With
upper bearing half seated in connecting rod, install connecting rod guides. These
guides
hold the upper
bearing half in place and prevent damage to the

crankshaft
crankpin during installation of the con­
necting rod and piston assembly.

d.
Be certain that the gap in the oil ring rails faces

upward,
toward center of
engine.
Gaps of the com­
pression rings shall not be aligned with each other

or
with the oil ring
rails.

e. Lubricate the piston and rings. Compress the
rings with a suitable piston ring compressor; install
the piston and connecting rod assembly from top of cylinder bore. Refer to Fig. Dl-33.

f.
Install
bearing cap, with lower bearing half, on connecting rod. Torque bolt nuts to 30 to 40 lb-ft. [4,1 a 5,5 kg-m.].
g.
Install
all other piston and connecting rod as­
semblies in same manner.

h.
Check
end clearance
between
connecting rods
on each crankpin with a feeler
gauge.
Clearance should be .005,/ to .012" [0,127 a
0,305
mm.].

Dl-76.
Install
Oil
Pump
Intake
Pipe
and
Screen Assembly

Check
mating surfaces of oil pump intake pipe

and
engine
cylinder block to be certain that they

are
clean. Secure the pipe and screen assembly,
with a new gasket, to
engine
cylinder block with two attaching screws. See Fig. Dl-34. Torque screws 6 to 9 lb-ft. [0,83 a 1,24 kg-m.].

Dl-77.
Install
Oil Pan

Refer
to Fig. Dl-35.

Be
certain the flange surface of oil pan and cor­
responding surface of
engine
cylinder block are
clean.
Install
a new oil pan gasket on the cylinder
block.
Secure
oil pan to cylinder block with mount­ ing bolts. Torque
bolts
10 to 15 lb-ft [1,4 a 2,1

kg-m.].

Dl-78.
Install
Flywheel

Refer
to Fig. Dl-7.

a.
Check
flywheel flange of
engine
crankshaft and corresponding surface of flywheel to
be
certain that
FIG.
Dl-33—INSTALLING
PISTON
AND

CONNECTING
ROD
ASSEMBLY
1—Ring
Compressor

FIG.
Dl-34-^-OIL
PUMP
INTAKE PIPE
AND

SCREEN
INSTALLATION
1—Pipe and Screen
97

'Jeep'
UNIVERSAL SERIES SERVICE
MANUAL

Dl
both are clean. Any foreign material on either of

these
surfaces
will
cause flywheel run out and en­
gine
vibration. Position flywheel to crankshaft and
secure with six mounting bolts. Torque mounting
bolts
50 to 65 lb-ft. [6,91 a 8,98 kg-m.].

Note:
Flywheel mounting
bolts
are unevenly
spaced so that flywheel can be installed in only
one position.
This
assures correct balance of fly­
wheel and crankshaft.

b.
Mount a
dial
indicator on flywheel housing
flange of cylinder block and index its plunger to
the flywheel surface. Measure flywheel run out.

Maximum
allowable run out is .015"
[0,381
mm.].
Dl-82.
Install
Cylinder
Head Assembly

Refer
to Fig. Dl-9.

a.
Wipe cylinder head face of
engine
cylinder
block, and be certain no foreign material has fallen
into the cylinder bores, bolt holes, or in the valve

lifter
area.
It is
good
practice to clean out bolt

holes
with compressed air.

b.
Install
a new cylinder head gasket on the
cylin­

der
block. Dowels in the block
will
hold the gasket

in
position. Always handle gaskets carefully to

avoid
kinking or damage to the surface treatment
of the gasket. Apply Perfect Seal Aerosol
Spray
Sealer
Part
No.
994757
on cylinder head gaskets.

Dl-79.
Install
Clutch
and Flywheel Housing

a.
Note
marks made on clutch assembly and fly­
wheel during
engine
disassembly. Position clutch
assembly to flywheel, according to
marks,
and
fasten
loosely
with six attaching bolts. Torque

bolts
in rotation, one
turn
at a time, to 30 to 40 lb-ft. [4,1 a 5,5 kg-m.].

b.
Engage fork of clutch linkage to clutch and
position flywheel housing to
engine
cylinder block.
Secure
housing to block with six mounting bolts.

Torque
bolts
30 to 40 lb-ft. [4,1 a 5,5 kg-m.].

D1-80.
Install
Camshaft

Insert
camshaft into camshaft bearings of
engine

cylinder
block carefully to avoid damage to bear­
ing surfaces. Make certain camshaft journals are

properly
seated in bearings.
12695

FIG.
D1-36—CAMSHAFT
AND
VALVE LINKAGE
1—
Rocker
Arm

2—
Push
Rod 3—
Valve
Lifter

4—
Camshaft
14203

FIG.
Dl-37—CYLINDER
HEAD
BOLT TIGHTENING SEQUENCE c.
Clean
gasket surface of cylinder head and care­

fully
place on the
engine
block dowel pins.

d.
Clean
and lubricate the cylinder head
bolts
with

a
sealing compound
(Part
No. 994757, or equiv­

alent).

e.
Install,
and alternately tighten the head bolts,
a
little at a time, in the sequence shown in Fig.

Dl-37.
Torque
bolts
65 to 85 lb-ft. [9,0 a 11,8

kg-m.].

f.
Tilt
the rocker arms toward the push rods and locate the top of each push rod in its rocker arm
seat.

g.
Mount the rocker arm and shaft assembly, tightening the bracket
bolts
a little at a time.
Torque
the bracket
bolts
25 to 35 lb-ft. [3,5 a 4,8

kg-m.].
Do not overtighten.

h.
See Section Fl and F2 for
engines
equipped

with
exhaust emission control.

D1-81.
Install
Valve Lifter
and Push Rod

Make
certain valve lifter guide
holes
and adjacent
area
of cylinder block are clean.
Liberally
lubricate
the camshaft and valve lifter bores with
engine

oil,
and install valve lifters.
Each
valve lifter must slide freely in its guide hole. See Fig. Dl-36.
Dl-83.
Install
Rocker Arm Cover

Install
a new gasket on each rocker arm cover.
Secure
each rocker arm cover to corresponding

cylinder
head with four attaching screws.
Install

the positive crankcase ventilation valve on right

rocker
arm cover. 99

'Jeep*
UNIVERSAL
SERIES SERVICE
MANUAL

Dl
of packing are at top. Drive in a new shedder with

a
suitable punch. Stake the shedder in at least three places to secure it in position. Size the pack-
FIG.
Dl-39—INSTALLATION
OF
TIMING

CHAIN
AND
SPROCKET

1—
Camshaft
Sprocket 3—Timing
Chain

2—
Crankshaft
Sprocket 4—Timing
Marks

FIG.
Dl-40—FUEL
PUMP
ECCENTRIC
AND
DISTRIBUTOR
DRIVE GEAR
1—
Fuel
Pump
Eccentric
3—Camshaft
2—
Oil
Groove 4—Distributor Drive
Gear
ing by rotating a hammer handle, or similar smooth
tool, around it, as necessary, to obtain clearance
for the crankshaft vibration damper hub.

Dl-86.
Install
Timing
Chain
Cover

Note:
There
are five
bolts
which attach the timing

chain
cover directly to the cylinder block, and seven
bolts
which attach both the timing chain
cover and water pump to the cylinder block.

a.
If oil pump has not been removed from timing

chain
cover, remove fine slotted attaching screws,

oil
pump cover, gasket from timing chain cover. Completely pack the space around the oil pump gears with petroleum jelly.
There
must be no air
space left inside the pump. Secure oil pump cover

and
a new gasket to timing chain cover with five slotted attaching screws. Torque screws, alternately
and
evenly, 8 to 12 lb-ft [1,10 a 1,66 kg-m.].

Note:
Unless oil pump gears are packed with petro­
leum jelly, pump may not prime itself when
engine

is started.

b.
The gasket surfaces of the cylinder block and
timing chain cover must be smooth and clean. In­
stall
a new timing chain cover gasket and position

it
correctly on the cylinder block.

Note:
Two different timing chain cover gaskets
have been installed in production on V-6 engines.

At
any time the timing chain cover gasket is
replaced,
make sure the correct gasket is installed.

c.
Position timing chain cover to cylinder block.

Use
timing cover aligner and oil seal remover tool J-22248. Be certain that dowel pins
engage
dowel

pin
holes
before installing bolts.

d.
Lubricate
bolt threads before installation.
Install

the mounting
bolts
and torque 25 to 33 lb-ft. [3,5
a
4,6 kg-m.].

Note:
Some timing chain covers have two additional
bolts, one in each upper corner. If the timing chain
cover being installed on a crankcase with
these
two
holes
does
not have matching holes, the
holes

in
the crankcase must be plugged with two hex
socket screw plugs. The plug should be driven past
the face of the case to prevent interference with the timing chain cover. These
bolts
are not shown

in
Fig. Dl-41.

D1-87.
Install
Oil Pump

a.
Pack
•
oil pump gear pocket of timing chain
cover with petroleum jelly. Do not use chassis
lubricant.

b.
Install
gears so that petroleum jelly is forced
into every cavity of gear pocket and
between
the

teeth
of the gears.
Install
a new oil pump cover gasket.

Note:
Unless the pump is packed with petroleum

jelly,
it may not prime itself when the
engine
is

started.

c.
Mount oil pump cover on timing gear cover

with
five slotted attaching screws. Torque screws 101

'Jeep1
UNIVERSAL
SERIES
SERVICE
MANUAL

Dl

FIG.
D1-43—INTAKE
MANIFOLD
SEAL
INSTALLATION

1—Seal 2—Cylinder Head ing
hole
at left side of timing chain cover. If timing

chain
and sprockets have not been removed from
engine, install distributor with rotor in position
noted during distributor removal. Fasten distributor
to timing chain cover with retaining bracket and
mounting screws. If distributor is aligned, torque
screw
18 to 20 lb-ft. [2,5 a 2,8 kg-m.].

Dl-100.
Install Spark Plugs

Install
spark
plugs in cylinder heads. Torque 25
to 33 lb-ft. [3,5 a 4,6 kg-m.].
Install
spark
plug cable retainers on brackets welded to rocker arm
covers. Fit cables into retainers and connect to
spark
plugs, as indicated by cable numbers molded
into distributor cap and by
spark
plug firing order
pressed into each rocker arm cover.

Dl-101.
Install Intake Manifold
and
Carburetor
Assembly

a.
Install
a new rubber intake manifold seal at
front and
rear
rails
of cylinder block. Be sure
pointed ends of seals fit snugly against block and
cylinder
heads. See Fig. Dl-43.

b.
Set intake manifold in place on cylinder block

between
cylinder heads.
Thread
two cap
bolts
through manifold into each cylinder head as guide
bolts.
Lift
the manifold slightly and insert each
of two gaskets into position
between
manifold
and
corresponding cylinder head. Be certain that
the gasket is installed with its three apertures
FIG.
Dl-44—INTAKE
MANIFOLD

GASKET
INSTALLATION

1—Gasket
2—Guides Bolts aligned with ports of the head and manifold. One
gasket should be installed in position on the left
side, as shown in Fig. Dl-44, and its counterpart

reversed
for right side installation.

c.
Install
manifold attaching bolt in open bolt

hole
at right side of intake manifold. See
Fig.
Dl-46.
Open
bolt
hole
is held to
close
tolerances, so that
the bolt in this location serves to locate the mani­
fold front and
rear.

d.
Install
remaining manifold-to-cylinder head bolts, with longer
bolts
at forward location. Begin­
ning
with the number 1 and 2 bolts, see
Fig.
Dl-45,
tighten gradually and equally until both
bolts
are
snug.
This
will
prevent the manifold from shifting due to
full
torque being applied to only one bolt.

Then
continue in the sequence illustrated in Fig.

Dl-45
until the rest of the
bolts
are also snug.

Finally,
using the same sequence, torque all
bolts
to 45 to 55 lb-ft. [6,2 a 7,6 kg-m.].
12750

FIG.
Dl-45—INTAKE
MANIFOLD
BOLT
TIGHTENING
SEQUENCE

103

Dl

DAUNTLESS
V-6
ENGINE
e.
Connect electrical wiring harness to coolant
temperature sending unit. Connect two distributor leads to ignition coil. Connect fuel line
between

fuel pump and carburetor, vacuum
hose
between
distributor and carburetor, and crankcase vent
hose

to intake manifold
below
rear
of carburetor.
FIG.
D1-46—-INTAKE
MANIFOLD
INSTALLATION

1—Long Bolt 2—Open Bolt Hole
Dl-102.
ENGINE INSTALLATION

Install
the
engine
in the vehicle in the following
procedure listed
below:

a.
Attach suitable sling to
engine
lifting
eyes
and,
using a hoist, lift the
engine
from blocks or
engine
stand.
b. When
engine
is free of the stand lower it slowly

into
the
engine
compartment of the vehicle.

Note:
The
engine
and transmission must be lined
up to
engage
the main shaft and clutch plate spline
while sliding the
engine
rearward
into
the mounting
position.
c.
Install
and tighten up
bolts
securing
engine
to
flywheel housing.

d.
Install
and tighten front
engine
mounting bolts.

e.
Remove sling from the
engine.

I.
Connect exhaust pipes to right and
left
engine
manifolds.
g. Connect choke cable support bracket to
car­

buretor.

h.
Connect
engine
fuel
hoses
and fuel lines at right
frame
rail.

I.
Connect fuel lines.

j.
Mount
engine
starter motor assembly to
engine.
k.
Connect battery cable and wiring to
engine

starter
motor.

I.
Connect
engine
wiring harnesses to connectors
located on
engine
firewall.

Note:
On
engines
equipped with exhaust emission
control, replace the air pump, air distributor mani­
fold, and anti-backfire (gulp) valve. See Section F2.
m. Replace radiator, and secure with bolts,
n.
Replace and tighten right and
left
radiator sup­
port rods.
0. Connect upper and lower radiator
hoses
to the

engine.
p. Connect alternator wiring harness from connec­
tor at regulator,
q.
Replace air cleaner.
r.
Connect battery ground cable from the battery
to the
engine
and the
engine
ground strap,

s.
Replace the hood.

After
the
engine
is installed in the vehicle,
fill
radiator
with coolant and
engine
with oil (Refer to
Lubrication
Section B), then perform an
engine

Tune-up
and road
test
(Refer to Tune-up Sec­
tion C).

Dl-103.
FINAL IN-VEHICLE ADJUSTMENTS

a.
Clean
battery terminals and check battery.
b.
Check
ignition wires and connections.
c. Service carburetor air cleaner.

d.
Service positive crankcase ventilation valve.
e.
Check
fuel lines.
f. Gap and install new
spark
plugs.
g.
Check
distributor
points
and capacitor; replace
if
necessary.

h.
Check
ignition (distributor) timing; reset if
necessary. 1.
Check
carburetor adjustments; reset if necessary,

j.
With
engine
fully warmed up, tighten cylinder
head and manifold
bolts
and nuts to specified
torque.
Check
cylinder head
gaskets
and
bolts
for
air
or coolant leaks.

Note:
Tightness of cylinder head
bolts
should be
checked and corrected after 500 miles [800 km.]
of normal operation and again at 1000 miles [1600

km.].
k.
Check
fan belt tension; adjust if necessary.
I.
Check
for and correct any oil leak, fuel leak or
coolant leak. 104

'Jeep'
UNIVERSAL
SERIES SERVICE
MANUAL

Dl
Dl-104.
SERVICE
DIAGNOSIS

Poor Fuel Economy
Ignition Timing Late or Spark Advance Inoperative

Carburetor
Float Setting Too High
Accelerator Pump Improperly Adjusted
Fuel
Pump Pressure High

Fuel
Line
Leakage

Fuel
Pump Diaphragm Leakage
Cylinder
Compression Low
Valves Do Not Seat Properly
Spark
Plugs
Defective

Spark
Plug Cables
Defective

Ignition
Coil
or Capacitor
Defective

Carburetor
Air Cleaner Dirty

Brakes
Drag
Wheel Alignment Incorrect

Tire
Pressure Incorrect Odometer Inaccurate

Fuel
Tank
Cap Clogged or
Defective

Muffler or Exhaust Pipe Clogged or Bent

Lack
of
Power
Cylinder
Compression Low
Ingitdon Timing Late

Carburetor
or
Fuel
Pump Clogged or
Defective

Fuel
Lines Clogged
Air
Cleaner Restricted
Engine Temperature High Valves Do Not Seat Property

Valve
Timing Late Intake Manifold or Cylinder Head
Gasket Leaks
Muffler or Exhaust Pipe Clogged or Bent
Spark
Plugs Dirty or
Defective

Breaker
Point Gap Incorrect
Breaker
Points
Defective
Ignition
Coil
or Capacitor
Defective

Electrical
Connection Loose
Broken
Valve Spring

Broken
Piston Ring or Piston
Cylinder
Head Gasket
Defective

Distributor Cap Cracked

Low
Compression
Valves Not Seating Properly Piston Rings Seal Poorly
Valve
Spring Weak or Broken
Cylinder
Scored or Worn
Piston Clearance Too Great

Cylinder
Head Gasket Leaks

Burned
Valves and
Seats
Valves Stick or Are Too Loose in Guides
Valve
Timing Incorrect

Valve
Head and Seat Have Excessive Carbon
Engine Overheats

Valve
Spring Weak or Broken

Valve
Lifter Seized or Collapsed
Exhaust
System Clogged
Valves Sticking

Valve
Stem Warped

Valve
Stem Carbonized or Scored

Valve
Stem Clearance Insufficient in Guide

Valve
Spring Weak or Broken

Valve
Spring Distorted
Oil
Contaminated

Overheating
Cooling System Inoperative
Thermostat Inoperative Ignition Timing Incorrect

Valve
Timing Incorrect
Carbon
Accumulation Excessive

Fan
Belt Loose
Muffler or Exhaust Pipe Clogged or Bent

Oil
System Failure
Piston Rings Worn or Scored
Popping,
Spitting,
Detonation
Ignition Timing Incorrect

Carburetion
Improper

Carbon
Deposit
in Combustion
Chambers Excessive
Valves Not Seating Properly
Valve
Spring Broken
Spark
Plug Electrodes Burned
Water or Dirt in
Fuel
Fuel
Line
Clogged
Valve
Timing Incorrect

Excessive
Oil
Consumption
Piston Rings Stuck in Grooves, Weak,
Worn,
Broken, or Incorrectly Fitted

Crankshaft
Main Bearings or
Connecting Rod Bearings Have
Excessive Clearance
Gaskets or Oil Seals
Leak

Cylinder
Bores Worn, Scored,
Out-of-Round or Tapered
Pistons Have Too Great Clearance to Cylinder Bores
Connecting Rods Misaligned High Road Speed
High Temperature

Crankcase
Ventilation System Inoperative
Bearing Failure
Crankshaft
Bearing Journal Rough or Out-of-Round

Oil
Level Low
Oil
Leakage

Oil
Dirty
Oil
Pressure Low or Lacking
(Oil
Pump Failure)

Drilled
Passages
in Crankshaft or
Crankcase
Clogged

Oil
Screen Dirty
Connecting Rod Bent 105