Mitsubishi Montero (1991+). Manual — part 111

Fig. 6: Measuring Valve Stem-to-Guide Clearance - Typical

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Lower valve approximately 1/16" below valve seat. Push valve

stem against valve guide as far as possible. Adjust dial indicator to

zero. Push valve stem in opposite direction and note reading.

Clearance must be within specification.

If valve guide clearance exceeds specification, valves with

oversize stems may be used or valve guide must be replaced. On some

applications, a false guide is installed, then reamed to proper

specification. Valve guide reamer set is used to ream valve guide to

obtain proper clearance for new valve.

Reaming Valve Guide

Select proper reamer for valve stem. Reamer must be of

proper length to provide clean cut through entire length of valve

guide. Install reamer in valve guide and rotate to cut valve guide.

See Fig. 7.

Fig. 7: Reaming Valve Guides - Typical

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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

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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

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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