Isuzu N-Series. Manual - part 564

GENERAL ENGINE MECHANICAL 6A-13

Valve Thickness

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

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

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.

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 cyl-
inder head lower surface.
If the measured value exceeds the specified limit,
the valve seat insert must be replaced.

Valve Contact Width

1. Check the valve contact faces for roughness and

unevenness. Make smooth the valve contact sur-
faces.

Valve Thickness

mm (in)

Standard

Limit

4JB1
4JB1-TC

Inlet

1.79 (0.0705)

1.5 (0.06)

Exhaust

1.83 (0.0720)

4JG2

Inlet

1.41 (0.0555)

1.1 (0.043)

Exhaust

1.39 (0.0547)

4JH1-TC

Inlet

1.41 (0.0555)

1.1 (0.043)

Exhaust

1.38 (0.0543)

Standard

Degrees

45

°

N6A0129E

Valve Depression

mm (in)

Standard

Limit

4JB1
4JB1-TC

Inlet

0.73 (0.029)

1.28 (0.050)

Exhaust

0.70 (0.028)

1.20 (0.047)

4JG2
4JH1-TC

Inlet

1.1 (0.043)

1.6 (0.063)

Exhaust

N6A0132E

N6A3083E

6A-14 GENERAL ENGINE MECHANICAL

2. Measure the valve contact width.

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

Valve Seat Insert Replacement

Valve Seat Insert Removal

1. Arc weld the tire inside circumference (1) of the

valve seat insert (2).

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

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

3. Use a screwdriver (3) to pry the valve seat insert

free.
Take care not to damage the cylinder head (4).

4. Carefully remove carbon and other foreign material

from the cylinder head insert bore.

Valve Seat Insert Installation

1. Carefully place the attachment (1) (having a small-

er outside diameter than the valve seat insert) on
the valve seat insert (2).

Notice:
The smooth side of the attachment must contact the
valve seat insert.

2. Use a bench press (3) to gradually apply pressure

to the attachment and press the valve seat insert
into place.

Notice:
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 sur-

face.

Contact Width

mm (in)

Standard

Limit

Inlet

1.7 (0.0670)

2.2 (0.0866)

Exhaust

2.0 (0.0788)

2.5 (0.0984)

N6A3084E

N6A3085E

N6A3086E

GENERAL ENGINE MECHANICAL 6A-15

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.

Notice:
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 con-

tact 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 mea-

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

3. Visually inspect both ends of the push rod for ex-

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

Valve Seat Angle

degree

45

°

N6A3087E

N6A3088E

Push Rod Curvature Limit

mm (in)

0.4 (0.0157) or less

N6A3089E

N6A3090E

6A-16 GENERAL ENGINE MECHANICAL

Reassembly

1. Valve Guide

• Apply engine oil to the outside of the valve

guide.
Using special tool, drive in a new valve guide
from the rocker arm shaft side.
Valve guide replacer: 9-8523-1212-0

2. Valve Guide Oil Seal

• Using special tool, drive in a new oil seal 

Oil special tool, drive in a new oil seal
Oil seal installer: 5-8840-2033-0

3. Valve

• Apply engine oil to the outside of the valve

stem.

4. Valve Spring

• Attach the valve seat to the upper spring seat.

The painted area of the valve spring should be
facing downward.

5. Split Collar

• Use a spring compressor to push the valve

spring into position.

• Install the spring seat split collar.
• Set the split collar by tapping lightly around the

head of the collar with a rubber hammer.

Valve spring compressor: 9-8523-1423-0 (J-29760)

6. Rocker Arm Assembly

Tighten:
54 N

⋅m (5.5 kg⋅m/40 lb⋅ft)

N6A3068E

N6A3069E

N6A3070E

N6A3091E