Isuzu engine 4j series. Service manual - part 17

6A – 4

  GENERAL ENGINE MECHANICAL

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 surface
should be grinded to within specifications. If more than
limit of specification, it should be replaced.

NOTE:

The cylinder head lower face cannot be reground.

mm (in)

Standard

Limit

Cylinder Head
Lower Face
Warpage

0.05 (0.002)

or less

0.20 (0.0079)

Cylinder Head
Height

92 (3.622)

91.55 (3.6043)

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.

Exhaust Manifold Warpage

mm (in)

Standard

Limit

0.05 (0.002) or less

0.20 (0.0079)

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.

Depression Limit

mm (in)

                                                                                                                   

0.02 (0.0008)

                                                                                                                   

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GENERAL ENGINE MECHANICAL   6A – 5

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.

2. Inspect the inside of the combustion chamber, the hot

plug, and the hot plug machined faces for cracking
and other damage.
If cracking or damage is present, the cylinder head
must be replaced.

NOTE:

Be absolutely certain that there are no scratches or
protuberance on the combustion chamber surfaces
which will be in contact with the hot plug after it is
installed. There flaws will prevent the hot plug from
seating correctly.

Hot plug inspection

Inspection the hot plugs for excessive wear and other
damage. Replace the hot plugs if either of these
conditions are discovered.

Hot plug installation (4JG2 only)

1. Align the hot plug knock ball 

!

 with the cylinder head

groove 

"

 and tap it temporarily into position with a

plastic hammer.

2. Place an appropriate metal plate 

#

 thick over the hot

plug upper surface 

$

3. Use a press 

%

 to exert a pressure of 44130 - 53937N

(4500 - 5500 kg/9923 - 12128 lbs.) on the metal plate
covering the hot plug upper surface. This will drive the
hot plug into position.

4. Lightly tap the hot plug heads to make sure that they

are firmly seated.

5.  Repeat the procedure Steps 1-4 for the remaining hot

plugs.

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6A – 6

  GENERAL ENGINE MECHANICAL

CAUTION:

Do not apply pressure greater than that specified.
Damage to the cylinder head will result.
6. Use a surface grinder to grind off any hot plug surface

protuberances.
The hot plug surfaces must be perfectly flush with the
cylinder head.

7. After grinding, make sure that the hot plug surfaces

are completely free of protuberances.
The hot plug surfaces must also be free of
depressions.

Once again, lightly tap the hot plug heads to make sure
that they are firmly seated.

Heat shield removal (4JG2 only)

After removing the hot plugs, use a hammer 

!

 and a

brass bar 

"

 to lightly tap the lower side of the heat shield

#

 and drive it free.

Heat shield installation (4JG2 only)

Install the heat shield washer and the heat shield to the
cylinder head from the nozzle holder installation hole side.
Lightly tap the flange into place with a brass bar.
The heat shield flange side must be facing up.

NOTE:

Always install a new heat shield. Never reuse the old
heat shield.

REASSEMBLY

6. Cylinder Head

1) Hot plug

•

Set the nock ball in the positioning groove on the
cylinder head side according to the order of the
cylinders, and hit it lightly with a plastic hammer.

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GENERAL ENGINE MECHANICAL   6A – 7

NOTE:
After being pressed into the cylinder head, the hot
plugs were provided with surface grinding.
Accordingly, their dimensions are different
individually among them, and take care not confuse
the order of the cylinders

.

When replacing the hot plug with new one:

When assembling a new hot plug, set the knock ball in the
positioning groove on the cylinder side and hit it lightly with
a plastic hammer until the hot plug is set in stably.
With patch attached to the hot plug to prevent it from
being damaged, press it in with a force of 4.5 to 5.5 ton
applied.
After pressing the hot plug, grind its surface to the cylinder
head.
And finally, hit the hot plug lightly with a plastic hammer
and check it for any excessive sinking, protrusion or
backlash.

2) Valve Seat Insert Installation

1. Carefully place the attachment 

!

 (having a smaller

outside diameter than the valve seat insert) on the
valve seat insert 

"

.

NOTE:

The smooth side of the attachment must contact the
valve seat insert.

2. Use the bench press 

#

 to gradually apply pressure to

the attachment and press the valve seat insert into
place.

NOTE:

Do not apply an excessive amount of pressure with
the bench press. Damage to the valve seat will

result.
Measure the height of the valve guide upper end from the
upper face of the cylinder head.

Valve Guide Upper End Height (H) (Reference)

mm (in)

                                                                                                                   

13 (0.51)

                                                                                                                   

NOTE:

If the valve guide has been removed, both the valve
and the valve guide must be replaced as a set.

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