width JEEP CHEROKEE 1994 Service User Guide

stalled, its rotational position can not be changed.
Do not attempt to modify the distributor housing
to get distributor rotation. Distributor position
will have no effect on ignition timing.
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
IGNITION COIL
Battery voltage is supplied to the ignition coil pos-
itive terminal from the ASD relay.
The Powertrain Control Module (PCM) opens and
closes the ignition coil ground circuit for ignition coil
operation.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to
set the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
The ignition coil is mounted to a bracket on the
side of the engine (Fig. 11).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
ENGINE COOLANT TEMPERATURE SENSOR
The engine coolant temperature sensor provides an
input voltage to the Powertrain Control Module
(PCM) relating coolant temperature. The PCM uses
this input, along with inputs from other sensors, to
determine injector pulse width and ignition timing.
Fig. 8 Sensor OperationÐ2.5L Engine
Fig. 9 Sensor OperationÐ4.0L EngineÐAll Except
YJ Models With Automatic Transmission
Fig. 10 Sensor OperationÐ4.0L EngineÐYJ Models
With Automatic Transmission
8D - 4 IGNITION SYSTEMSJ

As coolant temperature varies, the sensor resistance
will change, resulting in a different input voltage to
the PCM.
When the engine is cold, the PCM will operate in
the Open Loop Cycle. It will demand slightly richer
air-fuel mixtures and higher idle speeds, until nor-
mal operating temperatures are reached. Refer to
Modes Of Operation in Group 14, Fuel System for a
description of Open and Closed Loop operation.
This sensor is installed in the thermostat housing
(Fig. 12).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
INTAKE MANIFOLD AIR TEMPERATURE SENSOR
The sensor element extends into the intake mani-
fold air stream. It provides an input voltage to the
Powertrain Control Module (PCM) indicating intakemanifold air temperature. The input from this sensor
is used along with inputs from other sensors to de-
termine injector pulse width. As the temperature of
the air-fuel stream in the manifold varies, the sensor
resistance will change. This will result in a different
input voltage to the PCM. For more information, re-
fer to Group 14, Fuel System.
This sensor is installed in the intake manifold (Fig.
13, 4.0L engine or Fig. 14, 2.5L engine).
For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor reacts to absolute pressure in the
intake manifold and provides an input voltage to the
Powertrain Control Module (PCM). As engine load
changes, manifold pressure varies, causing the MAP
Fig. 11 Ignition CoilÐTypical
Fig. 12 Coolant Temperature SensorÐTypical
Fig. 13 Air Temperature Sensor LocationÐ4.0L
Engine
Fig. 14 Air Temperature Sensor LocationÐ2.5L
Engine
JIGNITION SYSTEMS 8D - 5

current engine operating conditions. It will also ad-
just fuel injector pulse width and ignition timing.For component testing, refer to the Diagnostics/Ser-
vice Procedures section of this group.
For removal and installation of this component, re-
fer to the Component Removal/Installation section of
this group.
Fig. 18 Throttle Position SensorÐ2.5L EngineFig. 19 Throttle Position SensorÐ4.0L Engine
JIGNITION SYSTEMS 8D - 7

ENGINES
CONTENTS
page page
2.5L ENGINE SERVICE PROCEDURES....... 9
4.0L ENGINE SERVICE PROCEDURES...... 50ENGINE DIAGNOSIS...................... 5
STANDARD SERVICE PROCEDURES......... 1
STANDARD SERVICE PROCEDURES
INDEX
page page
Engine Performance....................... 2
Form-In-Place Gaskets..................... 1
Honing Cylinder Bores..................... 2
Hydrostatic Lock.......................... 4Measuring with Plastigage................... 3
Repair Damaged or Worn Threads............ 4
Service Engine Assembly (Short Block)......... 4
FORM-IN-PLACE GASKETS
There are several places where form-in-place gas-
kets are used on the engine.DO NOT use form-in-
place gasket material unless specified.Care must
be taken when applying form-in-place gaskets. Bead
size, continuity and location are of great importance.
Too thin a bead can result in leakage while too much
can result in spill-over. A continuous bead of the
proper width is essential to obtain a leak-free joint.
Two types of form-in-place gasket materials are
used in the engine area (Mopar Silicone Rubber Ad-
hesive Sealant and Mopar Gasket Maker). Each have
different properties and cannot be used interchange-
ably.
MOPAR SILICONE RUBBER ADHESIVE
SEALANT
Mopar Silicone Rubber Adhesive Sealant, normally
black in color, is available in 3 ounce tubes. Moisture
in the air causes the sealant material to cure. This
material is normally used on flexible metal flanges.
It has a shelf life of a year and will not properly cure
if over aged. Always inspect the package for the ex-
piration date before use.
MOPAR GASKET MAKER
Mopar Gasket Maker, normally red in color, is
available in 6 cc tubes. This anaerobic type gasket
material cures in the absence of air when squeezed
between smooth machined metallic surfaces. It will
not cure if left in the uncovered tube. DO NOT use
on flexible metal flanges.
SURFACE PREPARATION
Parts assembled with form-in-place gaskets may be
disassembled without unusual effort. In some in-
stances, it may be necessary to lightly tap the part
with a mallet or other suitable tool to break the seal
between the mating surfaces. A flat gasket scraper
may also be lightly tapped into the joint but care
must be taken not to damage the mating surfaces.
Scrape or wire brush all gasket surfaces to remove
all loose material. Inspect stamped parts to ensure
gasket rails are flat. Flatten rails with a hammer on
a flat plate, if required. Gasket surfaces must be free
of oil and dirt. Make sure the old gasket material is
removed from blind attaching holes.
GASKET APPLICATION
Assembling parts using a form-in-place gasket re-
quires care.
Mopar Silicone Rubber Adhesive Sealant should be
applied in a continuous bead approximately 3 mm
(0.12 inch) in diameter. All mounting holes must be
circled. For corner sealing,a3or6mm(1/8 or 1/4
inch) drop is placed in the center of the gasket con-
tact area. Uncured sealant may be removed with a
shop towel. Components should be torqued in place
while the sealant is still wet to the touch (within 10
minutes). The use of a locating dowel is recom-
mended during assembly to prevent smearing the
material off location.
Mopar Gasket Maker should be applied sparingly
to one gasket surface. The sealant diameter should
be 1.00 mm (0.04 inch) or less. Be certain the mate-
rial surrounds each mounting hole. Excess material
JENGINES 9 - 1

(3) Honing should be done by moving the hone up
and down fast enough to get a crosshatch pattern.
The hone marks should INTERSECT at 50É to 60É for
proper seating of rings (Fig. 1).
(4) A controlled hone motor speed between 200 and
300 RPM is necessary to obtain the proper crosshatch
angle. The number of up and down strokes per
minute can be regulated to get the desired 50É to 60É
angle. Faster up and down strokes increase the cross-
hatch angle.
(5) After honing, it is necessary that the block be
cleaned to remove all traces of abrasive. Use a brush
to wash parts with a solution of hot water and deter-
gent. Dry parts thoroughly. Use a clean, white, lint-
free cloth to check that the bore is clean. Oil the
bores after cleaning to prevent rusting.
MEASURING WITH PLASTIGAGE
CRANKSHAFT MAIN BEARING CLEARANCE
Engine crankshaft bearing clearances can be deter-
mined by use of Plastigage, or equivalent. The fol-
lowing is the recommended procedures for the use of
Plastigage:
(1) Remove oil film from surface to be checked.
Plastigage is soluble in oil.
(2) The total clearance of the main bearings can
only be determined by removing the weight of the
crankshaft. This can be accomplished by either of
two methods:
METHOD - 1 (PREFERRED)ÐShim the bear-
ings adjacent to the bearing to be checked. This will
remove the clearance between upper bearing shell
and the crankshaft. Place a minimum of 0.254 mm
(0.010 inch) shim between the bearing shell and the
adjacent bearing cap. Tighten the bolts to 18 Nzm (13
ft. lbs.) torque.
²ALL ENGINESÐWhen checking No.1 main bear-
ing; shim No.2 main bearing.²ALL ENGINESÐWhen checking No.2 main bear-
ing; shim No.1 and No.3 main bearing.
²ALL ENGINESÐWhen checking No.3 main bear-
ing; shim No.2 and No.4 main bearing.
²ALL ENGINESÐWhen checking No.4 main bear-
ing; shim No.3 and No.5 main bearing.
²2.5L ENGINEÐWhen checking No.5 main bear-
ing; shim No.4 main bearing.
²4.0L ENGINEÐWhen checking No.5 main bear-
ing; shim No.4 and No.6 main bearing.
²4.0L ENGINEÐWhen checking No.6 main bear-
ing; shim No.5 and No.7 main bearing.
²4.0L ENGINEÐWhen checking No.7 main bear-
ing; shim No.6 main bearing.
Remove all shims before assembling engine.
METHOD - 2 (ALTERNATIVE)ÐThe weight of
the crankshaft is supported by a jack under the coun-
terweight adjacent to the bearing being checked.
(3) Place a piece of Plastigage across the entire
width of the bearing cap shell (Fig. 2). Position the
Plastigage approximately 6.35 mm (1/4 inch) off cen-
ter and away from the oil holes. In addition, suspect
areas can be checked by placing the Plastigage in
that area. Tighten the bearing cap bolts of the bear-
ing being checked to 108 Nzm (80 ft. lbs.) torque.DO
NOT rotate the crankshaft or the Plastigage may
be smeared, giving inaccurate results.
(4) Remove the bearing cap and compare the width
of the flattened Plastigage with the scale provided on
the package (Fig. 3). Plastigage generally comes in 2
scales (one scale is in inches and the other is a met-
ric scale). Locate the band closest to the same width.
This band shows the amount of clearance. Differ-
ences in readings between the ends indicate the
amount of taper present. Record all readings taken
(refer to Engine Specifications).
(5) Plastigage is available in a variety of clearance
ranges. The 0.025-0.076 mm (0.001-0.003 inch) range
is usually the most appropriate for checking engine
bearing clearances.
Fig. 1 Cylinder Bore Crosshatch Pattern
Fig. 2 Placement of Plastigage in Bearing Shell
JENGINES 9 - 3

CONNECTING ROD BEARING CLEARANCE
Engine connecting rod bearing clearances can be
determined by use of Plastigage, or equivalent. The
following is the recommended procedures for the use
of Plastigage:
(1) Remove oil film from surface to be checked.
Plastigage is soluble in oil.
(2) Place a piece of Plastigage across the entire
width of the bearing cap shell (Fig. 2). Position the
Plastigage approximately 6.35 mm (1/4 inch) off cen-
ter and away from the oil holes. In addition, suspect
areas can be checked by placing the Plastigage in the
suspect area.
(3) The crankshaft must be turned until the con-
necting rod to be checked starts moving toward the
top of the engine. Only then should the rod cap with
Plastigage in place be assembled. Tighten the rod
cap nut to 45 Nzm (33 ft. lbs.) torque.DO NOT ro-
tate the crankshaft or the Plastigage may be
smeared, giving inaccurate results.
(4) Remove the bearing cap and compare the width
of the flattened Plastigage with the scale provided on
the package (Fig. 3). Plastigage generally comes in 2
scales (one scale is in inches and the other is a met-
ric scale). Locate the band closest to the same width.
This band shows the amount of clearance. Differ-
ences in readings between the ends indicate the
amount of taper present. Record all readings taken
(refer to Engine Specifications).
(5) Plastigage is available in a variety of clearance
ranges. The 0.025-0.076 mm (0.001-0.003 inch) range
is usually the most appropriate for checking engine
bearing clearances.
REPAIR DAMAGED OR WORN THREADS
Damaged or worn threads can be repaired. Essen-
tially, this repair consists of:
²Drilling out worn or damaged threads.
²Tapping the hole with a special Heli-Coil Tap, or
equivalent.
²Installing an insert into the tapped hole.
This brings the hole back to its original thread size.
CAUTION: Be sure that the tapped holes maintain
the original center line.Heli-Coil tools and inserts are readily available
from automotive parts jobbers.
SERVICE ENGINE ASSEMBLY (SHORT BLOCK)
A service replacement engine assembly (short
block) may be installed whenever the original cylin-
der block is defective or damaged beyond repair. It
consists of the cylinder block, crankshaft, piston and
rod assemblies. If needed, the camshaft must be pro-
cured separately and installed before the engine is
installed in the vehicle.
A short block is identified with the letter ``S'' stamped
on the same machined surface where the build date
code is stamped for complete engine assemblies.
Installation includes the transfer of components
from the defective or damaged original engine. Fol-
low the appropriate procedures for cleaning, inspec-
tion and torque tightening.
HYDROSTATIC LOCK
When an engine is suspected of hydrostatic lock
(regardless of what caused the problem), follow the
steps below.
(1) Perform the Fuel Pressure Release Procedure
(refer to Group 14, Fuel System).
(2) Disconnect the negative cable from the battery.
(3) Inspect air cleaner, induction system and in-
take manifold to ensure system is dry and clear of
foreign material.
(4) Place a shop towel around the spark plugs to
catch any fluid that may possibly be under pressure in
the cylinder head. Remove the plugs from the engine.
CAUTION: DO NOT use the starter motor to rotate
the crankshaft. Severe damage could occur.
(5) With all spark plugs removed, rotate the crank-
shaft using a breaker bar and socket.
(6) Identify the fluid in the cylinders (i.e. coolant,
fuel, oil, etc.).
(7) Make sure all fluid has been removed from the
cylinders.
(8) Repair engine or components as necessary to
prevent this problem from occurring again.
(9) Squirt engine oil into the cylinders to lubricate
the walls. This will prevent damage on restart.
(10) Install new spark plugs. Tighten the spark
plugs to 37 Nzm (27 ft. lbs.) torque.
(11) Drain engine oil. Remove and discard the oil
filter.
(12) Install the drain plug. Tighten the plug to 34
Nzm (25 ft. lbs.) torque.
(13) Install a new oil filter.
(14) Fill engine crankcase with the specified
amount and grade of oil (refer to Group 0, Lubrica-
tion and Maintenance).
(15) Connect the negative cable to the battery.
(16) Start the engine and check for any leaks.
Fig. 3 Clearance Measurement
9 - 4 ENGINESJ

INSPECTION
Inspect for cracks in the combustion chambers and
valve ports.
Inspect for cracks on the exhaust seat.
Inspect for cracks in the gasket surface at each
coolant passage.
Inspect valves for burned, cracked or warped heads.
Inspect for scuffed or bent valve stems.
Replace valves displaying any damage.
VALVE REFACING
(1) Use a valve refacing machine to reface the in-
take and exhaust valves to the specified angle.
(2) After refacing, a margin of at least 0.787 mm
(0.031 inch) must remain (Fig. 8). If the margin is
less than 0.787 mm (0.031 inch), the valve must be
replaced.
VALVE SEAT REFACING
(1) Install a pilot of the correct size in the valve
guide bore. Reface the valve seat to the specified an-
gle with a good dressing stone. Remove only enough
metal to provide a smooth finish.
(2) Use tapered stones to obtain the specified seat
width when required.
(3) Control valve seat runout to a maximum of
0.0635 mm (0.0025 in.)Ð(Fig. 9).
VALVE STEM OIL SEAL REPLACEMENT
Valve stem oil seals are installed on each valve
stem to prevent rocker arm lubricating oil from en-
tering the combustion chamber through the valve
guide bores. One seal is marked INT (intake valve)
and the other is marked EXH (exhaust valve).Replace the oil seals whenever valve service is per-
formed or if the seals have deteriorated.
VALVE GUIDES
The valve guides are an integral part of the engine
cylinder head and are not replaceable.
When the valve stem guide clearance is excessive,
the valve guide bores must be reamed oversize. Ser-
vice valves with oversize stems are available in 0.076
mm (0.003 inch) and 0.381 mm (0.015 inch) incre-
ments.
Corresponding oversize valve stem seals are also
available and must be used with valves having 0.381
mm (0.015 inch) oversize stems.
If the valve guides are reamed oversize, the
valve seats must be ground to ensure that the
valve seat is concentric to the valve guide.
VALVE STEM-TO-GUIDE CLEARANCE
MEASUREMENT
Valve stem-to-guide clearance may be measured by
either of the following two methods.
PREFERRED METHOD:
(1) Remove the valve from the head.
(2) Clean the valve stem guide bore with solvent
and a bristle brush.
(3) Insert a telescoping gauge into the valve stem
guide bore approximately 9.525 mm (.375 inch) from
the valve spring side of the head (Fig. 10).
(4) Remove and measure telescoping gauge with a
micrometer.
(5) Repeat the measurement with contacts length-
wise to engine cylinder head.
(6) Compare the crosswise to lengthwise measure-
ments to determine out-of-roundness. If the measure-
ments differ by more than 0.0635 mm (0.0025 in.),
ream the guide bore to accommodate an oversize
valve stem.
Fig. 8 Valve Facing Margin
Fig. 9 Measurement of Valve Seat Runout
J2.5L ENGINE 9 - 23

Plastigage across full width of the lower insert at the
center of bearing cap. Plastigage must not crumble
in use. If brittle, obtain fresh stock.
(6) Install bearing cap and connecting rod on the
journal and tighten nuts to 45 Nzm (33 ft. lbs.)
torque. DO NOT rotate crankshaft. Plastigage will
smear, resulting in inaccurate indication.
(7) Remove the bearing cap and determine amount
of bearing-to-journal clearance by measuring the
width of compressed Plastigage (Fig. 7). Refer to En-
gine Specifications for the proper clearance.Plasti-
gage should indicate the same clearance across
the entire width of the insert. If the clearance
varies, it may be caused by either a tapered
journal, bent connecting rod or foreign material
trapped between the insert and cap or rod.
(8) If the correct clearance is indicated, replace-
ment of the bearing inserts is not necessary. Remove
the Plastigage from crankshaft journal and bearing
insert. Proceed with installation.
(9) If bearing-to-journal clearance exceeds the spec-
ification, install a pair of 0.0254 mm (0.001 inch) un-
dersize bearing inserts. All the odd size inserts must
be on the bottom. The sizes of the service replace-
ment bearing inserts are stamped on the backs of the
inserts. Measure the clearance as described in the
previous steps.
(10) The clearance is measured with a pair of
0.0254 mm (0.001 inch) undersize bearing inserts in-
stalled. This will determine if two 0.0254 mm (0.001
inch) undersize inserts or another combination is
needed to provide the correct clearance (refer to Con-
necting Rod Bearing Fitting Chart).FOR EXAMPLE:If the initial clearance was
0.0762 mm (0.003 inch), 0.025 mm (0.001 inch) un-
dersize inserts would reduce the clearance by 0.025
mm (0.001 inch). The clearance would be 0.002 inch
and within specification. A 0.051 mm (0.002 inch)
undersize insert would reduce the initial clearance
an additional 0.013 mm (0.0005 inch). The clearance
would then be 0.038 mm (0.0015 inch).
(11) Repeat the Plastigage measurement to verify
your bearing selection prior to final assembly.
(12) Once you have selected the proper insert, in-
stall the insert and cap. Tighten the connecting rod
bolts to 45 Nzm (33 ft. lbs.) torque.
Fig. 7 Measuring Bearing Clearance with Plastigage
CONNECTING ROD BEARING FITTING CHART
9 - 36 2.5L ENGINEJ

BEARING-TO-JOURNAL CLEARANCE (CRANKSHAFT
INSTALLED)
When using Plastigage, check only one bearing
clearance at a time.
Install the grooved main bearings into the cylinder
block and the non-grooved bearings into the bearing
caps.
Install the crankshaft into the upper bearings dry.
Place a strip of Plastigage across full width of the
crankshaft journal to be checked.
Install the bearing cap and tighten the bolts to 108
Nzm (80 ft. lbs.) torque.
DO NOT rotate the crankshaft. This will cause
the Plastigage to shift, resulting in an inaccurate
reading. Plastigage must not be permitted to
crumble. If brittle, obtain fresh stock.
Remove the bearing cap. Determine the amount of
clearance by measuring the width of the compressed
Plastigage with the scale on the Plastigage envelope
(Fig. 5). Refer to Engine Specifications for the proper
clearance.
Plastigage should indicate the same clearance
across the entire width of the insert. If clearance var-
ies, it may indicate a tapered journal or foreign ma-
terial trapped behind the insert.
If the specified clearance is indicated and there are
no abnormal wear patterns, replacement of the bear-
ing inserts is not necessary. Remove the Plastigage
from the crankshaft journal and bearing insert. Pro-
ceed to Crankshaft Main BearingÐInstallation.
If the clearance exceeds specification, install a pair
of 0.025 mm (0.001 inch) undersize bearing inserts
and measure the clearance as described in the previ-
ous steps.
The clearance indicated with the 0.025 mm (0.001
inch) undersize insert pair installed will determine if
this insert size or some other combination will pro-
vide the specified clearance.FOR EXAMPLE:If the clearance was 0.0762 mm
(0.003 inch) originally, a pair of 0.0254 mm (0.001
inch) undersize inserts would reduce the clearance by
0.0254 mm (0.001 inch). The clearance would then be
0.0508 mm (0.002 inch) and within the specification.
A 0.051 mm (0.002 inch) undersize bearing insert
and a 0.0254 mm (0.001 inch) undersize insert would
reduce the original clearance an additional 0.0127
mm (0.0005 inch). The clearance would then be
0.0381 mm (0.0015 inch).
CAUTION: Never use a pair of inserts that differ
more than one bearing size as a pair.
FOR EXAMPLE:DO NOT use a standard size up-
per insert and a 0.051 mm (0.002 inch) undersize
lower insert.
If the clearance exceeds specification using a pair
of 0.051 mm (0.002 inch) undersize bearing inserts,
measure crankshaft journal diameter with a mi-
crometer. If the journal diameter is correct, the
crankshaft bore in the cylinder block may be mis-
aligned, which requires cylinder block replacement
or machining to true bore.
If journals 1 through 5 diameters are less than
63.4517 mm (2.4981 inches), replace crankshaft or
grind crankshaft down to accept the appropriate un-
dersize bearing inserts.
Once the proper clearances have been obtained,
proceed to Crankshaft Main BearingÐInstallation.
MAIN BEARING JOURNAL DIAMETER (CRANKSHAFT
REMOVED)
Remove the crankshaft from the cylinder block (re-
fer to Cylinder Block - Disassemble).
Clean the oil off the main bearing journal.
Determine the maximum diameter of the journal
with a micrometer. Measure at two locations 90É
apart at each end of the journal.
The maximum allowable taper and out of round is
0.013 mm (0.0005 inch). Compare the measured di-
ameter with the journal diameter specification (Main
Bearing Fitting Chart). Select inserts required to ob-
tain the specified bearing-to-journal clearance.
Once the proper clearances have been obtained,
proceed to Crankshaft Main BearingÐInstallation.
INSTALLATION
(1) Lubricate the bearing surface of each insert
with engine oil.
(2) Loosen all the main bearing caps. Install the
main bearing upper inserts.
(3) Install the lower bearing inserts into the main
bearing caps.
(4) Install the main bearing cap(s) and lower in-
sert(s).
(5) Clean the rear main bearing cap (No.5) mating
surfaces.
Fig. 5 Measuring Bearing Clearance with Plastigage
9 - 42 2.5L ENGINEJ

gle with a good dressing stone. Remove only enough
metal to provide a smooth finish.
(2) Use tapered stones to obtain the specified seat
width when required.
(3) Control valve seat runout to a maximum of
0.0635 mm (0.0025 in.)Ð(Fig. 7).
VALVE STEM OIL SEAL REPLACEMENT
Valve stem oil seals are installed on each valve
stem to prevent rocker arm lubricating oil from en-
tering the combustion chamber through the valve
guide bores. One seal is marked INT (intake valve)
and the other is marked EXH (exhaust valve).
Replace the oil seals whenever valve service is per-
formed or if the seals have deteriorated.
VALVE GUIDES
The valve guides are an integral part of the engine
cylinder head and are not replaceable.
When the valve stem guide clearance is excessive,
the valve guide bores must be reamed oversize. Ser-
vice valves with oversize stems are available in 0.076
mm (0.003 inch) and 0.381 mm (0.015 inch) incre-
ments.
Corresponding oversize valve stem seals are also
available and must be used with valves having 0.381
mm (0.015 inch) oversize stems.
If the valve guides are reamed oversize, the
valve seats must be ground to ensure that the
valve seat is concentric to the valve guide.
VALVE STEM-TO-GUIDE CLEARANCE
MEASUREMENT
Valve stem-to-guide clearance may be measured by
either of the following two methods.
PREFERRED METHOD:
(1) Remove the valve from the head.
(2) Clean the valve stem guide bore with solvent
and a bristle brush.
(3) Insert a telescoping gauge into the valve stemguide bore approximately 9.525 mm (.375 inch) from
the valve spring side of the head (Fig. 8).
(4) Remove and measure telescoping gauge with a
micrometer.
(5) Repeat the measurement with contacts length-
wise to engine cylinder head.
(6) Compare the crosswise to lengthwise measure-
ments to determine out-of-roundness. If the measure-
ments differ by more than 0.0635 mm (0.0025 in.),
ream the guide bore to accommodate an oversize
valve stem.
(7) Compare the measured valve guide bore diam-
eter with specifications (7.95-7.97 mm or 0.313-0.314
inch). If the measurement differs from specification
by more than 0.076 mm (0.003 inch), ream the guide
bore to accommodate an oversize valve stem.
ALTERNATIVE METHOD:
(1) Use a dial indicator to measure the lateral
movement of the valve stem (stem-to-guide clear-
ance). This must be done with the valve installed in
its guide and just off the valve seat (Fig. 9).
(2) Correct clearance is 0.025-0.0762 mm (0.001-
0.003 inch). If indicated movement exceeds the spec-
ification ream the valve guide to accommodate an
oversize valve stem.
Valve seats must be ground after reaming the
valve guides to ensure that the valve seat is con-
centric to the valve guide.
VALVE SPRING TENSION TEST
Use Valve Spring Tester C-647 and a torque
wrench to test each valve spring for the specified ten-
sion value (Fig. 10).
Fig. 7 Measurement of Valve Seat Runout
Fig. 8 Measurement of Valve Guide Bore Diameter
9 - 64 4.0L ENGINEJ