Isuzu NHR 4J Series, Workshop Manual

Page: 176 / 406

4JB1/4JB1T/4JB1TC/4JG2 – ENGINE 6A1 – 41
INSTALLATION
20. Cylinder Head Gasket
Cylinder head gasket is determined by the piston head
projection from the cylinder body upper surface, in order to
improve engine performance.
Three types of gasket are provided by the difference of
thickness. Select the adequate one out of three grades of
gasket, according to the following procedure.
Before measurement, clear off carbon from the piston
head and cylinder body surface and also clean the place
where a gasket was installed.
Piston Head Projection Measurement Point
1) Use a dial indicator to measure the piston projection
amount.
2) Refer to the illustration for the piston head projection
measuring positions.
All measuring positions should be as close as possible
to the cylinder liner.
3) Measure the points
!"#$
and obtain two
differences
!
-
"
and
#
-
$
on each cylinder.
Calculate the average value of the piston head
projection on each cylinder.
4) Obtain the maximum value in the four cylinders.
5) Determine the gasket grade required to the maximum
value described above in accordance with the
following table.
4JB1/4JB1T/4JB1TC Cylinder Head Gasket Thickness
mm (in)
Gasket Grade Mark Piston
Projection
Gasket Thickness
(Reference)
A
0.758 - 0.813
(0.030 - 0.032)
1.60
(0.0630)
B
0.813 - 0.859
(0.032 - 0.034)
1.65
(0.0650)
C
0.859 - 0.914
(0.034 - 0.036)
1.70
(0.0670)
NOTE:
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).
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