Isuzu NHR 4J Series, Workshop Manual

Page: 117 / 406

6A – 50 GENERAL ENGINE MECHANICAL
NOTE:
It is most important that the correct piston grade be
used. Failure to select the correct piston grade will
result in engine failure. Always measure the cylinder
bore and select the correct piston grade.
Piston rings
Any worn or damaged part discovered during engine
overhaul must be replaced with a new one.
1. Ring end gap measurement
•
Insert the piston ring into the bore.
• Push the ring by the piston, at a right angle to the wall,
into the point ring at which the cylinder bore diameter
is the smallest.
• The top mark of the piston ring are shown in the
illustration.
4JB1 / 4JB1T / 4JB1TC mm.(in)
Standard Limit
1st 0.20 - 0.40
(0.0079 - 0.0157)
Compression
ring
2nd 0.20 - 0.40
(0.0079- 0.0157)
Oil ring
0.10 - 0.30
(0.0039 - 0.0118)
1.5
(0.059)
4JG2 mm.(in)
Standard Limit
1st 0.20 - 0.35
(0.0079 - 0.0138)
Compression
ring
2nd 0.37 - 0.52
(0.0146 - 0.0205)
Oil ring
0.20 - 0.40
(0.0079 - 0.0157)
1.5
(0.059)
2. Measure the clearance between the piston ring groove
and the piston ring with a feeler gauge. If the piston
ring groove/piston ring clearance exceeds the
specified limit, the piston must be replaced.
4JB1 / 4JB1T / 4JB1TC mm (in)
Standard Limit
1st 0.090 - 0.125
(0.0035 - 0.0049)
Compression
ring
2nd 0.050 - 0.075
(0.0020 - 0.0030)
Oil ring
0.03 - 0.07
(0.0012 - 0.0028)
0.15
(0.0059)
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