Mitsubishi S4Q User Manual page 74

PISTONS, CONNECTING RODS,
CRANKSHAFT AND CRANKCASE
Measuring
directions
Measuring
points
Figure 131 Checking crankcase bore
Figure 132 Measuring piston diameter
74 / 174
10.2.4 Crankcase
1. Checking crankcase bore
1)
Piston available
Size
Standard
0.25
[0.0098]
oversize
0.50
[0.0197]
oversize
Out-of-round and
taper of bores
2)
a
b
Perpendicular
to piston pin
c
ENGLISH
ENGINE MAIN PARTS
Measure the entire bore with a cylinder bore
gage having a dial indicator. Take
measurements at A, B and C positions in the
bore on axes 90° apart, as shown in the
illustration, to check the diameter, out-of-
round and taper. If the bores exceeds the
service limit for diameter, out-of-round and
taper, increase them for oversize pistons.
Bore Diameter
Size
Assembly Standard
Code
+0.035
STD 88 [3.46
0
+0.035
25 88.25 [3.4744
0
+0.035
50 88.50 [3.4842
0
0.015 [0.0006] or less
Boring of cylinders
There are two piston oversizes (0.25 mm
[0.0098 in.] and 0.50 mm [0.0197 in.] over
standard size) as listed above. Determine the
piston size to be used based on the largest
bore diameter of the cylinders.
Measure the outside diameter of the piston to
be used.
Based on the measurement of the piston
outside diameter, calculate the finishing
dimension to be achieved by boring.
A : Measured piston outside diameter selected
oversized piston) mm
B : Clearance between piston and cylinder
(standard value) 0.03 mm [0.0012 in.]
C : Honing allowance 0.04 mm [0.0016 in.] or
less
Finishing dimension = A + B - C
Service Manual Mitsubishi SQ-Series diesel engines
Unit: mm [in.]
Service
Limit
+0.0014
]
0
+0.0014
]
0
+0.2
[+0.008]
+0.0014
]
0
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Version 08/2004