Isuzu N-Series. Manual - part 561

GENERAL ENGINE MECHANICAL 6A-1

ENGINE 4J SERIES

SECTION 6A

GENERAL ENGINE MECHANICAL

Contents

CYLINDER HEAD ................................................. 6A-2

Component ........................................................ 6A-2
Disassembly ...................................................... 6A-2
Clean ................................................................. 6A-3
Inspection and Repair........................................ 6A-3
Reassembly....................................................... 6A-6

VALVE SPRING, VALVE GUIDE OIL SEAL, VALVE 
GUIDE, PUSH ROD............................................ 6A-10

Component ...................................................... 6A-10
Disassembly .................................................... 6A-10
Inspection and Repair...................................... 6A-11
Reassembly..................................................... 6A-16

CAMSHAFT, TAPPET ........................................ 6A-17

Component ...................................................... 6A-17
Disassembly .................................................... 6A-17
Inspection and Repair...................................... 6A-18
Reassembly..................................................... 6A-21

ROCKER ARM ASSEMBLY ............................... 6A-25

Component ...................................................... 6A-25
Disassembly .................................................... 6A-25
Inspection and Repair...................................... 6A-25
Reassembly..................................................... 6A-27

OIL PUMP ........................................................... 6A-28

Component ...................................................... 6A-28
Removal .......................................................... 6A-28
Installation ....................................................... 6A-29

CRANKSHAFT.................................................... 6A-30

Component ...................................................... 6A-30
Disassembly .................................................... 6A-30
Inspection and Repair...................................... 6A-31
Reassembly..................................................... 6A-35

PISTON AND CONNECTING ROD .................... 6A-47

Component ...................................................... 6A-47
Disassembly .................................................... 6A-47
Inspection and Repair...................................... 6A-48
Reassembly..................................................... 6A-53

CYLINDER BLOCK............................................. 6A-57

Component ...................................................... 6A-57
Disassembly .................................................... 6A-57
Inspection and Repair...................................... 6A-58
Reassembly..................................................... 6A-61

6A-2 GENERAL ENGINE MECHANICAL

CYLINDER HEAD

Component

Notice:

• During disassembly, be sure that the valve train

components are kept together and identified so
that they can be re-installed in their original loca-
tions.

• Before removing the cylinder head from the engine

and before disassembling the valve mechanism,
make a compression test and note the results.

Disassembly

1. Thermostat Housing Assembly
2. Injection Nozzle Holder (4JG2)
3. Injection Nozzle Holder (4JB1, 4JB1-TC)
4. Injection Nozzle Holder (4JH1-TC)

1) Remove the nozzle holder bracket nuts.

Legend

1. Thermostat housing assembly

6. Glow plug and plug connector (4JB1, 4JB1-TC)

2. Injection nozzle holder (4JG2)

7. Rocker arm shaft and rocker arm

3. Injection nozzle holder (4JB1, 4JB1-TC)

8. Push rod

4. Injection nozzle holder (4JH1-TC)

9. Cylinder head

5. Glow plug and plug connector (4JG2)

N6A3052E

N6A3437E

GENERAL ENGINE MECHANICAL 6A-3

2) Use the nozzle holder remover and the sliding

hammer to remove the nozzle holder together
with the holder bracket.
Nozzle Holder Remover: 5-8840-2034-0
Sliding Hammer: 5-8840-0019-0

5. Glow Plug and Glow Plug Connector (4JG2)
6. Glow Plug and Glow Plug Connector (4JB1, 4JB1-

TC, 4JH1-TC)

7. Rocker Arm Shaft and Rocker Arm
8. Push Rod
9. Cylinder Head

• Loosen the cylinder head bolts a little at a time

in the numerical order shown in the illustration.

Notice:
Failure to loosen the cylinder head bolts a little at a time
in numerical order will adversely effect the cylinder head
lower surface.

Clean

• Cylinder head bolts
• Cylinder head

Carefully remove all varnish, soot and carbon to
the bare metal. Do not use a motorized wire brush
on any gasket sealing surface.

Inspection and Repair

Make the necessary adjustments, repairs, and part re-
placements if excessive wear or damage is discovered
during inspection.

• Cylinder head gasket and mating surfaces for

leaks, corrosion and blow-by. If the gasket has
failed, determine the cause;

– Improper installation
– Loose or warped cylinder head
– Insufficient torque on head bolts
– Warped case surface

1. Cylinder head bolts for damaged threads or

stretching and damaged heads caused by improp-
er use of tools.

Caution:
Suspected bolts must be replaced.

2. Cylinder head for cracks, especially between valve

seats and in the exhaust ports. 

3. Cylinder head deck for corrosion, sand particles in

head and porosity.

Caution:
Do not attempt to weld the cylinder head. Replace it.

4. Cylinder head deck, intake and exhaust manifold

mating surfaces for flatness.
These surfaces may be re-conditioned by milling
(except cylinder head lower face). If the surfaces
are “out of flat” by more than specification, the sur-
face should be ground to within specifications. If
more than limit of specification, it should be re-
placed.

N6A3054E

N6A3055E

N6A3056E

6A-4 GENERAL ENGINE MECHANICAL

Notice:
The cylinder head lower face cannot be reground.

5. Water jacket sealing plugs seating surfaces.
6. Use a straight edge and a feeler gauge to measure

the manifold cylinder head lifting face warpage.
Regrind the exhaust manifold cylinder head lifting
surfaces if the measured values are between the
specified limit and the standard. 
If the measured values exceed the specified limit,
the manifold must be replaced.

Hot Plug Depression (4JG2 only)

1. Clean the cylinder head lower side, taking care not

to damage the hot plug surfaces.

2. Use a straight edge and feeler gauge to measure

hot plug depression in a straight line from the No.
1 hot plug to the No. 4 hot plug. 
If the measured value exceeds the limit, the hot
plugs must be replaced.

Hot Plug Removal (4JG2 only)

1. Insert a 3.0 — 5.0 (0.12 — 0.20.) diameter bar into

the nozzle holder fitting hole unit it makes contact
with the hot plug.

2. Lightly tap the bar with a hammer to drive the hot

plug free.
If the measured value exceeds the limit, the hot
plugs must be replaced.

Combustion Chamber Inspection (4JG2 only)

1. Remove the carbon adhering to the inside of the

combustion chamber. Take care not to damage the
hot plug fitting positions.

mm (in)

Standard

Limit

Standard Limit
Cylinder Head
Lower Face

0.05 (0.002) or 

less

0.20 (0.0079)

Cylinder Head
Height 

92 (3.622) 

91.55 (3.6043)

Exhaust Manifold Warpage

mm (in)

Standard

Limit

0.05 (0.002) or less

0.20 (0.0079)

Depression Limit

mm (in)

0.02 (0.0008)

N6A3057E

N6A3058E

N6A3059E