Mitsubishi Montero (1998+). Manual — part 140
Fig. 7: Reaming Valve Guides - Typical
This Graphic For General Information Only
Replacing Valve Guide
Replace valve guide if clearance exceeds specification. Valve
guides are either pressed, hammered or shrunk in place, depending upon
cylinder head design and type of metal used.
Remove valve guide from cylinder head by pressing or tapping
on a stepped drift. See Fig. 8. Once valve guide is installed,
distance from cylinder head to top of valve guide must be checked.
This distance must be within specification.
Aluminum heads are often heated before installing valve
guide. Guide is sometimes chilled in dry ice before installation.
Combination of a heated head and chilled guide insures a tight guide
fit upon assembly. The new guide must be reamed to specification.
Fig. 8: Typical Valve Guide Remover & Installer
This Graphic For General Information Only
VALVES & VALVE SEATS
Valve Grinding
Valve stem O.D. should be measured in several areas to
indicate amount of wear. Replace valve if not within specification.
Valve margin area should be measured to ensure that valve can be
grounded. See Fig. 9.
Fig. 9: Measuring Valve Head Margin - Typical
This Graphic For General Information Only
If valve margin is less than specification, this will burn
the valves. Valve must be replaced. Due to minimum margin dimensions
during manufacture, some new type valves cannot be reground.
Resurface valve on proper angle specification using valve
grinding machine. Follow manufacturer’s instructions for valve
grinding machine. Specifications may indicate a different valve face
angle than seat angle.
Measure valve margin after grinding. Replace valve if not
within specification. Valve stem tip can be refinished using valve
grinding machine.
Valve Lapping
During valve lapping of recent designed valves, be sure to
follow manufacturers recommendations. Surface hardening and materials
used with some valves do not permit lapping. Lapping process will
remove excessive amounts of the hardened surface.
Valve lapping is done to ensure adequate sealing between
valve face and seat. Use either a hand drill or lapping stick with
suction cup attached.
Moisten and attach suction cup to valve. Lubricate valve stem
and guide. Apply a thin coat of fine valve grinding compound between
valve and seat. Rotate lapping tool between the palms or with hand
drill.
Lift valve upward off the seat and change position often.
This is done to prevent grooving of valve seat. Lap valve until a
smooth polished seat is obtained. Thoroughly clean grinding compound
from components. Valve to valve seat concentricity should be checked.
See VALVE SEAT CONCENTRICITY.
CAUTION: Valve guides must be in good condition and free of carbon
deposits prior to valve seat grinding. Some engines contain
an induction hardened valve seat. Excessive material removal
will damage valve seats.
Valve Seat Grinding
Select coarse stone of correct size and angle for seat to be
ground. Ensure stone is true and has a smooth surface. Select correct
size pilot for valve guide dimension. Install pilot in valve guide.
Lightly lubricate pilot shaft. Install stone on pilot. Move stone off
and on the seat approximately 2 times per second during grinding
operation.
Select a fine stone to finish grinding operation. Grinding
stones with 30 and 60 degree angles are used to center and narrow the
valve seat as required. See Fig. 10.
Fig. 10: Adjusting Valve Seat Width - Typical
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Valve Seat Replacement
Replacement of valve seat inserts is done by cutting out
the old insert and machining an oversize insert bore. Replacement
oversize insert is usually chilled and the cylinder head is sometimes
warmed. Valve seat is pressed into the head. This operation requires
specialized machine shop equipment.
Valve Seat Concentricity
Using dial gauge, install gauge pilot in valve guide.
Position gauge arm on the valve seat. Adjust dial indicator to zero.
Rotate arm 360 degrees and note reading. Runout should not exceed
specification.
To check valve-to-valve seat concentricity, coat valve face
lightly with Prussian Blue dye. Install valve and rotate it on valve
seat. If pattern is even and entire seat is coated at valve contact
point, valve is concentric with the seat.
REASSEMBLY
Valve Stem Installed Height
Valve stem installed height must be checked when new valves
are installed or when valves or valve seats have been ground. Install
valve in valve guide. Measure distance from tip of valve stem to
spring seat. See Fig. 11. Distance must be within specifications.
Fig. 11: Measuring Valve Stem Installed Height - Typical
This Graphic For General Information Only
Remove valve and grind valve stem tip if height exceeds
specification. Valve tips are surface hardened. DO NOT remove more
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