Isuzu N-Series. Service 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
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