Isuzu N-Series. Manual - part 385

6C-18 FUEL SYSTEM

Inspection

Injection Nozzle Needle

1. Remove the nozzle from the nozzle body.
2. Carefully wash the nozzle needle and the nozzle

body in clean diesel fuel.

3. Check that the nozzle needle moves smoothly in-

side the injection nozzle body.
If the nozzle does not move smoothly, it must be
repaired (See “Nozzle Lapping Procedure” below).

Nozzle Lapping Procedure

1. Lap the nozzle needle (1) and the nozzle body (2)

by applying a compound of oxidized chrome and
animal oil (3).

Notice:
Do not apply an excessive amount of the oxidized
chrome and animal oil compound to the injection needle
valve seat area.

2. Carefully wash the needle valve and the nozzle

body in clean diesel fuel after lapping.

Nozzle Body and Needle Valve
Check the nozzle body and the needle valve for damage
and deformation.
The nozzle and body assembly must be replaced if ei-
ther of these two conditions are discovered during in-
spection.

Notice:
New nozzles must be cleaned in a solvent to remove
protective coating.
The nozzle body and needle must always be replace as
an assembly.

Reassembly

N6A0847E

N6A0850E

N6A0845E

FUEL SYSTEM 6C-19

1. Nozzle Holder Body
2. Adjusting Shim
3. Nozzle Spring
4. Spring Seat
5. Spacer
6. Injection Nozzle

Install the nozzle dowel pin with it set to the dowel
hose of the nozzle holder body.

7. Retaining Nut

Clamp the injection nozzle holder in a vice.
Tighten the injection nozzle holder retaining nut to
the specified torque.

Tighten:
Injection nozzle holder retaining nut to 34 N

⋅m (3.5 kg⋅m

/ 25 lb

⋅ft)

Remove the injection nozzle holder from the vice.

8. Flange

Adjustment of Injection Starting Pressure

After reassemble of the injection nozzle, recheck the
opening pressure and spray condition.
Opening Pressure
Attach the injection nozzle holder to the injection nozzle
tester.
Apply pressure to the nozzle tester to check that the in-
jection nozzle opens at the specified pressure.
If the injection nozzle does not open at the specified
pressure, install or remove the appropriate number of
adjusting shims to adjust it.

Legend

1. Flange
2. Retaining nut
3. Injection nozzle
4. Spacer
5. Spring seat
6. Nozzle spring
7. Adjusting shim
8. Nozzle holder body

N6A0852E

Injection Nozzle Opening 
Pressure

MPa (kg/cm

2

/psi)

4HF1/4HF1-2/4HG1

18.1 (185/2,631)

4HE1-TC

21.6 (220/3,128)

N6A0846E

N6A0843E

6C-20 FUEL SYSTEM

Opening Pressure Adjustment

1. Clamp the injection nozzle holder (1) in a vise (2).
2. Use a wrench to remove the injection nozzle retain-

ing nut (3).

3. Remove the injection nozzle holder from the vise.
4. Remove the injection nozzle (4), the spacer (5), the

spring seat (6) the spring (7) and the adjusting
shim (8).

5. Install the new adjusting shim, the spring, the sprig

seat, the spacer, the injection nozzle, and the re-
taining nut.

6. Clamp the injection nozzle holder in the vise.
7. Tighten the injection nozzle holder retaining nut to

the specified torque.

Tighten:
Injection nozzle holder retaining nut to 34 N

⋅m (3.5 kg⋅m

/ 25 lb

⋅ft)

8. Remove the injection nozzle holder from the vise.

9. Attach the injection nozzle holder to the injection

nozzle tester.

10. Apply pressure to the nozzle tester to check that

the injection nozzle opens at the specified pres-
sure.
If the injection nozzle does not open at the speci-
fied pressure, install or remove the appropriate
number or adjusting shims to adjust it.
Removing or installing one shim will increase or
decrease the nozzle opening pressure approxi-
mately 370 kPa (3.77 kg/cm

2

 / 53.6 psi).

Spray Pattern
Check the spray condition.
Refer to the illustration.
Spray Condition

• Correct (1)
• Incorrect (Restrictions in orifice) (2)
• Incorrect (Dripping) (3)

If the spray condition is bad, the injection nozzle must be
replaced or adjusted.

Refer to “Adjustment”.

Notice:
Adjust the nozzle in a well ventilated area. Do not inhale
oil or spray injected from the nozzle.

Disassembly

4-1 Injection Nozzle (Two spring nozzle holder)
(4HG1-T only)
The two-spring nozzle holder has been developed to re-
duce NOx (Nitrogen Oxides) and particulates from direct
injection diesel engine exhaust.

N6A0855E

N6A0856E

Adjusting Shim Availability

mm (in)

Range

0.5 — 1.5 (0.02 — 0.06)

Increment

0.025 (0.001)

Total Number of Shims

41

N6A0029E

FUEL SYSTEM 6C-21

1. Before disassembly remove carbon deposit from

nozzle and nozzle holder using a wire brush and
wash the outside nozzle holder assembly.

Caution:
Do not touch nozzle holes with the wire brush during
cleaning it.

2. Disassemble the nozzle holder assembly to nu-

merical order.

Reassembly and Opening Pressure Adjust-
ment

The nozzle holder is adjusted as the components are re-
assembled in the sequence above.
As adjustment of the two-spring nozzle holder is made
in hundredths of a millimeter, clean the parts thoroughly
in light oil to completely remove any dirt or foreign mat-
ter.
Reassembly and Adjustment Procedure

1. First nozzle opening pressure adjustment

• Adjust the first nozzle opening pressure using

the shim.

Legend

1. Retaining nut
2. Nozzle & pin
3. Spacer & pin
4. Lift piece
5. Spring seat
6. Push rod
7. Shim (Second nozzle opening pressure adjust-

ment)

8. Second spring
9. Collar

10. Spring seat

11. First spring

12. Shim (First nozzle opening pressure adjust-

ment)

13. Nozzle holder body
14. Eye bolt
15. Gasket

N6A0858E

Legend

1. Nozzle holder body
2. Shim (First opening pressure adjustment)
3. First spring
4. Spring seat
5. Collar
6. Second spring
7. Push rod
8. Shim (Second opening pressure adjustment)
9. Spring seat

10. Lift piece

11. Spacer & pin

12. Nozzle & pin
13. Retaining nut
14. Gasket
15. Eye bolt

N6A0859E