Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual — part 561

6A – 82 ENGINE MECHANICAL

ROCKER ARM SHAFT AND ROCKER
ARM

Rocker Arm Shaft Run-Out

1. Place the rocker arm shaft on a V-block.
2. Use a dial indicator to measure the rocker arm shaft

central portion run-out.
If the run-out is very slight, correct the rocker arm
shaft run-out with a bench press. The rocker arm must
be at cold condition.
If the measured rocker arm shaft run-out exceeds the
specified limit, the rocker arm shaft must be replaced.

Rocker Arm Shaft Run-Out

mm (in)

Limit

0.3 (0.012)

Rocker Arm Shaft Outside Diameter

Use a micrometer to measure the rocker arm fitting
portion outside diameter.
If the measured value is less than the specified limit, the
rocker arm shaft must be replaced.
Rocker Arm Shaft Outside Diameter

mm (in)

Standard

Limit

18.98 – 19.00 (0.747 – 0.748)

18.90 (0.744)

Rocker Arm Shaft and Rocker Arm Clearance

1. Use either a vernier caliper or a dial indicator to

measure the rocker arm inside diameter.

Rocker Arm Inside Diameter

mm (in)

Standard Limit

19.010 – 19.030

(0.748 – 0.749)

19.100 (0.752)

2. Measure the rocker arm shaft outside diameter.

If the measured value exceeds the specified limit,
replace either the rocker arm or the rocker arm shaft.

Rocker Arm Shaft and Rocker Arm
Clearance mm

(in)

Standard Limit

0.01 – 0.05

(0.0004 – 0.0020)

0.20 (0.008)

ENGINE MECHANICAL 6A – 83

VALVE SPRING

Valve Spring Free Height

Use a vernier caliper to measure the valve spring free
height.
If the measured value is less than the specified limit, the
valve spring must be replaced.
Inner and Outer Spring Free Height

mm (in)

Standard Limit

Inner spring 45.3 (1.78) 44.4 (1.75)

4JA1, 4JA1T,
4JA1TC

Outer spring 49.7 (1.96) 48.2 (1.90)

4JB1T,

4JG2T,

4JH1TC

Single spring 48.0 (1.89) 47.1 (1.85)

Valve Spring Squareness

Use a surface plate and a square to measure the valve
spring squareness.
If the measured value exceeds the specified limit, the
valve spring must be replaced.
Inner and Outer Spring Squareness

mm (in)

Limit

Inner

Spring

3.0

(0.120)

4JA1, 4JA1T,
4JA1TC

Outer Spring

3.2 (0.126)

4JB1T,

4JG2T,

4JH1TC

Single Spring

1.7 (0.07)

Valve Spring Tension

Use a spring tester to measure the valve spring tension.
If the measured value is less than the specified limit, the
valve spring must be replaced.
Valve Spring Tension

kg (lb/N)

Compressed

Height

Standard Limit

Inner
Spring

37.0 mm

(1.46 in)

5.9

(13.0/57.9)

5.0

(11.0/49.0)

4JA1,
4JA1T,
4JA1TC

Outer
Spring

39.0 mm

(1.54 in)

20.9

(46.0/205.0)

18.1

(39.8/177.4)

4JB1T,
4JG2T,
4JH1TC

Single
Spring

38.9 mm

(1.53 in)

30.2

(66.4/296.0)

26.3

(57.9/257.7)

6A – 84 ENGINE MECHANICAL

Valve Seat Insert Installation

1. Carefully place the attachment

Q

(having a smaller

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

R

.

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

S

to gradually apply pressure to

the attachment and press the valve seat insert into
place.

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

with the entire circumference of the valve.

ENGINE MECHANICAL 6A – 85

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.

Valve Contact Width

mm (in)

Standard

Limit

Intake 1.7

(0.067)

2.2

(0.087)

Exhaust

2.0 (0.079)

2.5 (0.078)

Valve Seat Insert Replacement

Valve Seat Insert Removal

1. Arc weld the entire inside circumference

Q

of the

valve seat insert

R

.

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

S

to pry the valve seat insert free.

Take care not to damage the cylinder head

T

.

4. Carefully remove carbon and other foreign material

from the cylinder head insert bore.