Isuzu N-Series. Manual - part 494

Engine Mechanical (4HK1-TC)   6A-81

• Press the tool against the oil seal. Strike the

tool to remove the seal from the inside of the
cylinder head.

Inspection

1. Inspect the cylinder head assembly.

• Remove varnish, soot and others adhered on

the metal surface completely. Use metal brush
and others so that the seal surface of the
surface where the gasket is installed is not
damage.

• Check the following causes in the case of leak

of the seal surface of the cylinder head,
corrosion, air leak and defective gasket.

- Defective installation.
- Defective tightening of the cylinder head.
- Winding seal surface of the cylinder block.

a. Damage on the screw surface or extracted

cylinder head bolt due to extra tightening torque

Caution:
Replace suspicious bolt.

b. Inside the combustion chamber, glow plug hole.

• Check whether there is a crack between the

valve sheets and in the cylinder head of the
exhaust port part, and replace the cylinder
head if there is serious damage or crack.
Check the collar if necessary.

c. Flatness of the under surface of the cylinder

head

• Use a straight edge ruler and thickness

gauge to measure the four sides and
diagonal lines as shown in the drawing, and
replace if they exceed the limit.

d. Flatness of the surface where the exhaust

manifold and inlet cover are installed

N6A6139E

Distortion of the under surface of the 
cylinder head 

mm (in)

Standard

0.05 (0.002) or less

Limit

0.20 (0.0079)

N6A6140E

N6A6141E

6A-82   Engine Mechanical (4HK1-TC)

• Use a straight edge ruler and thickness

gauge to measure the four sides and
diagonal lines as shown in the drawing, and
replace if they exceed the limit.

e. Flatness of the exhaust manifold

• Use a straight edge ruler and thickness

gauge to measure the flatness. If it exceeds
the limit, replace the exhaust manifold.

2. Bridge

• Make sure the bridge moves smoothly along

the bridge guide.

• Measure the gap between the bridge and

bridge guide.

Legend

1. Bridge
2. Bridge Guide

 

3. Inspect the valve guide.

Caution:
If there is a scratch or abnormal abrasion in the valve
stem and the inner diameter part of the valve guide,
replace it with new one along with valve guide.

a. Measure the valve guide clearance.

• Measure the diameter of the valve stem with

a micro meter.
If the diameter of the valve stem is smaller
than the limit, replace the valve and valve
stem altogether.

Distortion of the surface where the 
manifold and cover are installed

mm (in)

Standard

0.05 (0.002) or less

Limit

0.2 (0.0079)

Distortion of the exhaust manifold

mm (in)

Standard

0.3 (0.0118)or less

Limit

0.5 (0.0197)

N6A6142E

N6A6143E

Gap between the bridge guide and bridge
guide

mm (in)

Assembly standard

0.020 (0.00079) –

0.056 (0.00220)

Usage limit

0.1 (0.0039)

The external diameter of the valve 
stem

mm (in)

Standard

Limit

Intake valve

7.946 (0.3128) – 

7.961 (0.3134)

7.88 (0.3102)

Exhaust valve

7.921 (0.3118) – 

7.936 (0.3124)

7.80 (0.3071)

N6A6145E

Engine Mechanical (4HK1-TC)   6A-83

• Measure the gap between the valve guide

and valve stem within 10 mm (0.39 in) from
the valve guide, using a dial gauge.

• If the measured value exceeds the limit,

replace the valve guide and valve
altogether.

4. Inspect abrasion of the bridge gap.

• Measure the contact surface of bridge cap and

the rocker arm, using a dial gauge.

• If the abrasion exceeds the limit, or there is an

abnormal abrasion (zonal abrasion), replace
the bridge cap.

5. Inspect the valve.

Thickness of the valve

• Measure the thickness of the valve.
• If the measured value exceeds the limit, replace

the valve and valve guide altogether.

Gap between the valve guide and 
valve stem

mm (in)

Standard

Limit

Intake valve

0.039 (0.00153) – 

0.071 (0.00280)

0.20 (0.00787)

Exhaust valve

0.064 (0.00252) – 

0.096 (0.00378)

0.25 (0.00984)

N6A6146E

N6A6147E

Abrasion of the bridge cap

mm (in)

Limit

0.1 (0.00394)

Thickness of the valve

mm (in)

Standard

Limit

Intake valve

1.71 (0.0673)

1.3 (0.0512)

Exhaust valve

1.75 (0.0689)

1.3 (0.0512)

N6A6148E

N6A6149E

6A-84   Engine Mechanical (4HK1-TC)

Valve sheet

• Remove carbon, water stain and others on the

under surface of the cylinder head.
Install the valve in the cylinder head.
Measure the depth of the valve from the under
surface of the cylinder head, using a depth
gauge or straight edge ruler.
If it exceeds the limit, replace the valve insert or
cylinder head assembly.

• Measure the contact width of the valve seat. If

the seat contact surface has a scratch or is
rough, or if the abrasion of the contact surface
exceeds the limit, modify or replace it.

Contact surface of the valve seat

• If the contact surface of the valve seat is

defective, modify it or replace the valve, valve
guide and valve seat altogether.
Angle of the contact surface: 45

° (degrees)

Repair of the seat surface

• Remove carbon from the surface of the valve

insert seat.

Depth of the valve

mm (in)

Standard

0.7 (0.0276) – 1.2 (0.0472)

Limit

2.5 (0.0984)

Contact width of the valve seat

mm (in)

Standard

Limit

Intake valve

2.5 (0.0984)

3.0 (0.1181)

Exhaust valve

2.0 (0.0787)

2.5 (0.0984)

N6A6150E

N6A6151E

N6A6152E