Isuzu N-Series. Manual - part 589

6A1-44 4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE

4JH1

Notice:
The difference between the highest measured piston
head projection and the lowest measured piston head
projection must not exceed 1.0 mm (0.039 in).

2. Cylinder Head Assembly

1) Install the dowel in cylinder block.
2) Install the cylinder head gasket with top mark

up.

3) Clean up cylinder head lower surface and cylin-

der body upper surface.

4) Install the cylinder head as softly.
5) Apply engine oil to screw and seat of cylinder

head bolts.

6) Tighten the cylinder head bolts to the specified

torque in three steps following the numerical or-
der shown in the illustration.

Tighten:
Cylinder head bolts to 

• 1st step: 49 N

⋅m (5kg⋅m / 36 lb⋅ft)

• 2nd step: 60

° — 75°

• 3rd step: 60

° — 75°

3. Push Rod

• Apply engine oil to push rod and in to the cylinder

head.

4. Rocker Arm shaft

1) Loosen all adjusting screws.
2) Position the rocker arm shaft with the large oil

hole (4

φ) facing the front of the engine.

3) Tighten the rocker arm shaft bracket bolts to

the specified torque in the numerical order
shown in the illustration.

Legend

1. Grade mark

N6A3691E

N6A3218E

N6A3219E

N6A3119E

4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE 6A1-45

Tighten:

• Rocker arm shaft bracket bolt to 54 N

⋅m (5.5kg⋅m / 40

lb

⋅ft)

• Valve clearance adjustment.

Above works refer to “ROCKER ARM SHAFT AS-
SEMBLY” Section in this manual.

5. Cylinder Head Cover

• Apply engine oil to the rocker arms and the valve

spring.

• Install the cylinder head cover gasket to the cylin-

der head cover.

• The gasket must be perfectly smooth with no loose

areas.

• Tighten the cylinder head cover nuts to the speci-

fied torque in the numerical order shown in the il-
lustration.

Tighten:

• Cylinder head cover to 13 N

⋅m (1.3kg⋅m / 113 lb⋅in)

6. By-Pass Hose

7. Front Exhaust Pipe

• Install the pipe to manifold and tighten bolts and

nuts to the specified torque.

Tighten:

• W/Exhaust brake manifold nut to 37 N

⋅m (3.8 kg⋅m /

27 lb

⋅ft)

• WO/Exhaust brake manifold nut to 40 N

⋅m (4.1 kg⋅m

/ 30 lb

⋅ft)

• Pipe stay bolts to 40 N

⋅m (4.1kg⋅m / 30 lb⋅ft)

8. Vacuum Actuator Hose (Exhaust Brake Model)

• Install the vacuum hose to the vacuum actuator.

9. A/C Compressor Assembly (A/C Model)

• Install the A/C compressor fixing bolts and tighten

bolts to the specified torque.

Tighten:

• Compressor bolts to 37 N

⋅m (3.8 kg⋅m / 27 lb⋅ft)

N6A3091E

N6A3254E

N6A3294E

N6A3291E

6A1-46 4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE

10. Oil Cooler Water Pipe (Oil Cooler Model)

• Install the water pipe bolt and tighten bolt to the

specified torque.

Tighten:

• Water pipe nut to 19 N

⋅m (1.9 kg⋅m / 1.4 lb⋅ft)

• Pipe bracket bolt to 40 N

⋅m (4.1kg⋅m / 30 lb⋅ft)

11. Oil Level Gauge Guide Tube

• Install the guide tube bolt and tighten bolt to the

specified torque.

Tighten:

• Guide tube bolt to 19 N

⋅m (1.9 kg⋅m / 1.4 lb⋅ft)

12. Glow Plug Harness
13. PCV Hose

14. Leak Off Pipe

• Mount using a new copper washer.

15. Injection Pipe

• Install the flare nut to injection pump side.
• Install the flare nut to injection nozzle side.
• Tighten the flare nut to the specified torque.

Tighten:

• Flare nut to 29 N

⋅m (3.0 kg⋅m / 22 lb⋅ft)

N6A3290E

N6A3289E

N6A3288E

N6A3287E

4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE 6A1-47

• Fit pipe clip in specified torque.

Tighten:

• Sleeve nut to 29 N

⋅m (3.0 kg⋅m / 22 lb⋅ft)

16. Air Intake Duct
17. Engine Harness

• Connect the thermo-sensor harness and thermo-

meter unit harness.

18. A/C Compressor Drive Belt (A/C Model)

Check drive belts for wear or damage, and replace
with new ones as necessary. Check belts for ten-
sion, and adjust as necessary.

• Check drive belts tension.
• Push the middle of belts with a force of 10 kg

and check each bolt for deflection.

• Standard deflection

4JB1

Tension Adjustment
P/S oil pump and A/C compressor pulley belt

• With P/S pump lock bolt loose, adjust belt tension

with adjust belt.

Cooling fan pulley belt

• With AC Generator mounting and lock bolts loose,

adjust belt tension with adjuster’s adjust bolt.

Legend

1. Thermo-sensor

N6A3781E

N6A3286E

mm (in)

Initial tension

AC generator & fan pulley drive belt

8 — 12 (0.31 

— 0.47)

A/C compressor drive belt

P/S pump drive belt

Legend

1. A/C compressor drive belt & P/S pump drive 

belt

2. AC generator &fan pulley drive belt

N6A3295E