Isuzu N-Series. Manual — part 573
GENERAL ENGINE MECHANICAL 6A-49
The grading position for piston outside diameter is rep-
resented by the ‘G’ as shown in Figure.
Measure the cylinder bore inside diameter (refer to “in-
spection of the cylinder Block” in this Section).
If the piston clearance does not conform to the specified
valve, the piston and/or cylinder liners must be replaced.
Selection Method of Piston Grade for Service Parts.
If you find piston grade A from size mark or piston out-
side diameter measurement result, you will select AX for
service piston grade.
The stamped piston grade on the head of piston for ser-
vice parts.
Legend
1. G-mark
2. Front mark
4JG2
mm (in)
Size Mark
Outside Diameter
A
95.365 — 95.374 (3.7545 — 3.7549)
B
95.375 — 95.384 (3.7549 — 3.7553)
C
95.385 — 95.394 (3.7553 — 3.7557)
D
95.395 — 95.404 (3.7557 — 3.7561)
4JH1-TC
mm (in)
Size Mark
Outside Diameter
A
95.355 — 95.364 (37.5413 — 37.5449)
B
95.365 — 95.374 (37.5453 — 37.5488)
C
95.375 — 95.384 (37.5492 — 37.5528)
D
95.385 — 95.394 (37.5531 — 37.5567)
N6A3175E
Legend
1. G-mark
2. Front mark
Piston Clearance
mm (in)
4JB1 / 4JB1-TC
0.061 (0.0024)
4JG2
0.066 (0.0026)
4JH1-TC
0.057 — 0.075 (0.0022 —
0.0029)
Service piston grade
Piston Size Mark
Service Parts Grade
A
AX
B
AX
C
CX
D
CX
N6A3176E
6A-50 GENERAL ENGINE MECHANICAL
Notice:
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.
Service piston diameter
mm (in)
Piston Grade
4JB1 / 4JB1-TC
AX
92.989 — 93.004 (3.6610 — 3.6616)
CX
93.005 — 93.020 (3.6616 — 3.6622)
Piston Grade
4JG2
AX
95.369 — 95.384 (3.7547 — 3.7553)
CX
95.385 — 95.400 (3.7553 — 3.7559)
Piston Grade
4JH1-TC
AX
95.359 — 95.374 (3.7543 — 3.7549)
CX
95.375 — 95.390 (3.7549 — 3.7555)
N6A3177E
Legend
1. N mark (Top ring) (2nd ring) (4JB1)
2. 1N mark (Top ring) 2N mark (2nd ring) (4JG2)
3. R mark (Top ring) (2nd ring) (4JH-TC)
4JB1 / 4JB1-TC
mm (in)
Standard
Limit
Compression
ring
1st
0.20 — 0.40
(0.0079 — 0.0157
1.5
(0.059)
2nd
0.20 — 0.40
(0.0079 — 0.0157
Oil ring
0.10 — 0.30
(0.0039 — 0.0118)
4JG2
mm (in)
Standard
Limit
Compression
ring
1st
0.20 — 0.35
(0.0079 — 0.0138)
1.5
(0.059)
2nd
0.37 — 0.52
(0.0146 — 0.0205)
Oil ring
0.20 — 0.40
(0.0079 — 0.0157)
4JH1-TC mm
(in)
Standard
Limit
Compression
ring
1st
0.30 — 0.50
(0.0118 — 0.0197)
1.5
(0.059)
2nd
0.30 — 0.50
(0.0118 — 0.0197)
Oil ring
0.25 — 0.45
(0.0098 — 0.0117)
N6A3178E
GENERAL ENGINE MECHANICAL 6A-51
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 ex-
ceeds the specified limit, the piston must be re-
placed.
Piston Pin
Visually inspect the piston pin for cracks, flaws, and oth-
er damage and replace if necessary.
1. Use a micrometer to measure the piston pin out-
side diameter in both directions at three different
positions.
If the measurement exceed the specified limit the
piston pin must be replaced.
2. Measure the inside diameter of the connecting rod
small end. If the clearance between the small end
and pin does not conform to the specified value,
the connecting rod or bushing and pin must be re-
placed.
4JB1 / 4JB1-TC
mm (in)
Standard
Limit
Compression
ring
1st
0.090 — 0.125
(0.0035 — 0.0049)
1.5
(0.059)
2nd
0.050 — 0.075
(0.0020 — 0.0030)
Oil ring
0.03 — 0.07
(0.0012 — 0.0028)
4JG2
mm (in)
Standard
Limit
Compression
ring
1st
0.09 — 0.13
(0.0035 — 0.0051)
1.5
(0.059)
2nd
0.05 — 0.07
(0.0020 — 0.0028)
Oil ring
0.03 — 0.07
(0.0012 — 0.0028)
4JH1-TC
mm (in)
Standard
Limit
Compression
ring
1st
0.09 — 0.13
(0.0035 — 0.0051)
1.5
(0.059)
2nd
0.05 — 0.09 (0.002
— 0.0035)
Oil ring
0.03 — 0.07
(0.00118 — 0.0028)
N6A3179E
Piston pin outside diameter
mm (in)
Standard
Limit
4JB1
4JB1-TC
4JH1-TC
30.995 — 31.000
(1.2202 — 1.2204)
30.970 (1.2190)
4JG2
33.995 — 34.000
(1.3384 — 1.3386)
33.970 (1.3374)
mm (in)
Standard
Limit
Clearance
0.008 — 0.020
(0.0003 — 0.0008)
0.05 (0.0020)
N6A3180E
6A-52 GENERAL ENGINE MECHANICAL
3. Insert the piston pin into the piston and rotate it. If
the pin rotates smoothly with no backlash, the
clearance is normal. If there is backlash or rough-
ness, measure the clearance. If the clearance ex-
ceeds the specified limit, the piston and the piston
pin must be replaced.
Bushing Replacement
Removal: Use a suitable bar and bench press or ham-
mer.
Installation: Use a suitable bar and bench press.
Notice:
Align the bushing with the connecting rod oil port.
After installing a new bushing, finish the bushing bore
with a pin hole grinder.
Connecting Rods
1. Check the connecting rod alignment with a con-
necting rod aligner.
If either the bend or the twist exceeds the specified
limit, the connecting rod must be replaced.
2. Measure the connecting rod thrust clearance.
Use a feeler gauge to measure the thrust clear-
ance at the big end of the connecting rod.
If the clearance exceeds the specified limit, the
connecting rod must be replaced.
mm (in)
Standard
Limit
Clearance
0.002 — 0.004
(0.00008 — 0.00016)
0.04 (0.0016)
N6A3181E
N6A3182E
mm (in)
Standard
Limit
Bend per
100 (3.94)
0.08 (0.0031) or less
0.20 (0.0079)
Twist per
100 (3.94)
0.05 (0.0020) or less
0.15 (0.0059)
Thrust Clearance
mm (in)
Standard
Limit
0.230 (0.0091)
0.350 (0.0138)
N6A3183E
Нет комментариевНе стесняйтесь поделиться с нами вашим ценным мнением.
Текст