Isuzu N-Series. Manual - part 315

6A-2 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. Glow Plug Connector
2. Glow Plug
3. Injection Nozzle Holder Assembly

Mark the nozzle holder assemblies fitting positions
by tagging each nozzle holder assembly with the
cylinder number from which it was removed.

4. Rocker Arm Shaft Assembly

1) Loosen the rocker arm shaft bracket nuts and

bolts in numerical order a little at a time and re-
move the rocker arm shaft assembly with the
camshaft brackets.

2) Leave the (A) indicated bolt unremoved on this

occasion, since it is the rocker arm fixing bolt.

Caution:
Failure to loosen the rocker arm shaft bracket nuts and
bolts in numerical order a little at a time will adversely af-
fect the rocker arm shaft.

Legend

1. Glow plug connector

6. Camshaft bearing cap

2. Glow plug

7. Camshaft bearing upper

3. Injection nozzle holder assembly

8. Camshaft assembly

4. Rocker arm shaft assembly

9. Camshaft bearing lower

5. Valve cap

10. Cylinder head

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ENGINE MECHANICAL 6A-3

5. Valve Cap

Caution:
Take sufficient care not to let valve caps fall into the gear
case or oil return hole.

6. Camshaft Bearing Cap
7. Camshaft Bearing Upper
8. Camshaft Assembly
9. Camshaft Bearing Lower

If the camshaft bearings are to be reinstalled, mark
their fitting positions by tagging each bearing with
the cylinder number from which it was removed.

10. Cylinder Head

Loosen the cylinder head bolts in numerical order
a little at a time.

Caution:
Failure to loosen the cylinder head bolts in numerical or-
der a little at a time will adversely affect the cylinder
head lower surface.

• Refer to Section 6A3 “CYLINDER HEAD”.

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.

Cylinder Head Lower Face Warpage

1. Use a straight edge and a feeler gauge to measure

the four sides and the two diagonals of the cylinder
head face.

2. If the measured values exceed the specified limit,

the cylinder head must be replaced.

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6A-4 ENGINE MECHANICAL

Notice:
Do not regrind the cylinder head lower face.

Manifold Fitting Face Warpage

Use a straight edge and a feeler gauge to measure the
manifold cylinder head fitting face warpage.
Regrind the manifold cylinder head fitting faces if the
measured value is greater than the specified limit.

Exhaust Manifold Warpage

Use a straight edge and a feeler gauge to measure the
manifold cylinder head fitting face warpage.
If the measured values exceed the specified limit, the
manifold must be replaced.

Reassembly

Install the cylinder head gasket with its “PART NUM-
BER” mark facing up and toward the left of the engine.

Caution:
Do not reuse the cylinder head gasket.

Above works refer to “CYLINDER BLOCK” section in
this manual.

1. Cylinder Head

Cylinder Head Lower 
Face Warpage

mm (in)

Standard

Limit

0.05 (0.002) or less

0.2 (0.008)

Manifold Fitting Face 
Warpage

mm (in)

Standard

Limit

0.05 (0.002) or less

0.2 (0.008)

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Exhaust Manifold 
Warpage

mm (in)

Standard

Limit

0.05 (0.002) or less

0.24 (0.008)

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ENGINE MECHANICAL 6A-5

1) Align the cylinder body dowels and the cylinder

head dowel holes.

2) Carefully place the cylinder head on the cylin-

der head gasket.

3) Apply a coat of molybdenum disulfide grease to

the M14 cylinder head bolt threads and setting
faces and apply a coat of engine oil to the M10
cylinder head bolt threads and setting faces.

4) Use the angular tightening method to tighten

the bolts (M14) to the specified torque in three
steps following the numerical order shown in
the illustration.

Tighten:
Cylinder head bolt (M14: (1) — (18)) to

• 1st step: 98 N

⋅m (10 kg⋅m / 72 lb⋅ft)

• 2nd step: 147 N

⋅m (15 kg⋅m / 108 lb⋅ft)

• 3rd step: 30 — 60

°

5) Tighten the cylinder head to the flywheel hous-

ing bolts (M10) to the specified torque.

Tighten:
Cylinder head bolt to (M10: (19) — (20)) to 38 N

⋅m (3.9

kg

⋅m / 28 lb⋅ft)

2. Camshaft Bearing Lower
3. Camshaft Assembly

1) Turn the crankshaft in the direction of normal

rotation until the timing mark on the crankshaft
damper pulley is aligned with the TDC notched
line. (Confirm that the No. 1 cylinder piston
comes to the compression top dead center.)

2) Apply engine oil to the camshaft journal and the

camshaft bearing surfaces before installation.

3) Carefully align the camshaft gear “I” mark and

the cylinder head upper face shown in the illus-
tration.

4. Camshaft Bearing Upper
5. Camshaft Bearing Cap

1) Install the bearing caps with the bearing cap

head mark (arrow) facing forward.

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