Isuzu engine 4j series. Manual - part 19

6A – 12

  GENERAL ENGINE MECHANICAL

1. Valve Guide Clearance

•

Measure the valve stem diameter with a micrometer.
If the valve stem diameter is less than the specified
limit, the valve and the valve guide must be replaced
as a set.

mm (in)

Standard

Limit

Inlet

7.946 - 7.961

(0.3128 - 0.3134)

7.880

(0.310.2)

Diameter of
Valve stem

Exhaust

7.921 - 7.936

(0.3118 - 0.3124)

7.850

(0.3091)

•

Measure the inside diameter of the valve guide with a
micrometer.

•

Subtract the measured outer diameter of the valve
stem from the measured inner diameter of the valve
guide. If the valve exceeds of the valve guide.
If the valve exceeds the specified limit, the valve and
the valve guide must be replaced as a set.

Valve Guide Clearance

mm (in)

Standard

Limit

Inlet clearance

0.039 - 0.069

(0.0015 - 0.0027)

0.200

(0.0079)

Exhaust clearance

0.064 - 0.096

(0.0025 - 0.0038)

0.250

(0.0098)

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GENERAL ENGINE MECHANICAL   6A – 13

Valve Guide Replacement

1. Using special tool, drive out the valve guide from the

combustion chamber side.

Valve guide replacer: 9-8523-1212-0

2. Apply engine oil to the outside of the valve guide.

Using special tool, drive in a new valve guide from
cylinder head upper face side, and check the valve
guide height.

Valve guide replacer: 9-8523-1212-0
Height

mm (in)

                                                                                                                   

13 (0.51)

                                                                                                                   

NOTE:

If the valve guide has been removed, both the valve
and the valve guide must be replaced as a set.

Valve Thickness

1. Measure the valve thickness
2. If the measured value is less than the specified limit

the valve and the valve guide must be replaced as a
set.

Valve Thickness

mm (in)

Standard

Limit

Inlet

1.79 (0.0705)

4JB1
4JB1T
4JB1TC Exhaust

1.83 (0.0720)

1.5 (0.06)

Inlet

1.41 (0.0555)

4JG2

Exhaust

1.39 (0.0547)

1.1 (0.043)

Contact surface angle on valve seat on valve

1. Measure contact surface angle on valve seat.
2. If the measured value exceeds the limit, replace valve

guide and valve seat as a set.

Standard

Degrees

                                                                                                                   

45°

                                                                                                                   

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6A – 14

  GENERAL ENGINE MECHANICAL

Valve depression

1. Install the valve (1) to the cylinder head (2).
2. Use a depth gauge or a straight edge with steel rule to

measure the valve depression from the cylinder head
lower surface.
If the measured value exceeds the specified limit, the
valve seat insert must be replaced.

Valve Depression

mm (in)

Standard

Limit

Inlet

0.73 (0.029)

1.28 (0.050)

4JB1
4JB1T
4JB1TC Exhaust

0.70 (0.028)

1.20 (0.047)

Inlet

4JG2

Exhaust

1.1 (0.043)

1.6 (0.063)

Valve Contact Width

1. Check the valve contact faces for roughness and

unevenness. Make smooth the valve contact surfaces.

2. Measure the valve contact width.

If the measured value exceeds the specified limit, the
valve seat insert must be replaced.

Contact Width

mm (in)

Standard

Limit

Inlet

1.7 (0.0670)

2.2 (0.0866)

Exhaust

2.0 (0.0788)

2.5 (0.0984)

Valve Seat Insert Replacement

Valve Seat Insert Removal

1. Arc weld the tire inside circumference 

! 

of the valve

seat insert 

"

.

2. Allow the valve seat insert to cool for a few minutes.

This will invite contraction and make removal of the
valve seat insert easier.

3. Use a screwdriver 

#

 to pry the valve seat insert free.

Take care not to damage the cylinder head 

$

.

4. Carefully remove carbon and other foreign material

from the cylinder head insert bore.

Valve Seat Insert Installation

1. Carefully place the attachment 

!

 (having a smaller

outside diameter than the valve seat insert) on the
valve seat insert 

"

.

NOTE:

The smooth side of the attachment must contact the
valve seat insert.
2. Use a bench press 

#

 to gradually apply pressure to

the attachment and press the valve seat insert into
place.

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GENERAL ENGINE MECHANICAL   6A – 15

NOTE:

Do not apply an excessive amount of pressure with
the bench press. Damage to the valve seat insert will
result.

Valve Seat Insert Correction

1. Remove the carbon from the valve seat insert surface.
2. Use a valve cutter (15°, 45°, and 75° blades) to

minimize scratches and other rough areas, this will
bring the contact width back to the standard value.
Remove only the scratches and rough areas. Do not
cut away too much. Take care not to cut away
unblemished area of the valve seat surface.

Valve Seat Angle

degree

                                                                                                                   

45°

                                                                                                                   

NOTE:

Use an adjustable valve cutter pilot.

Do not allow the valve cutter pilot to wobble inside the
valve guide.
3. Apply abrasive compound to the valve seat insert

surface.

4.  Insert the valve into the valve guide.
5.  Turn the valve while tapping it to fit the valve seat

insert.

6. Check that the valve contract width is correct.
7. Check that the valve seat insert surface is in contact

with the entire circumference of the valve.

Push Rod Curvature

1. Lay the push rod on a surface plate.
2. Roll the push rod along the surface plate and measure

the push rod curvature with a thickness gauge.
If the measure value exceeds the specified limit, the
push rod must be replaced.

Push Rod Curvature Limit

mm (in)

                                                                                                                   

0.4 (0.0157) or less

                                                                                                                   

3. Visually inspect both ends of the push rod for

excessive wear and damage. The push rod must be
replaced if these conditions are discovered during
inspection.

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