Cylinder Block, Crankshaft, Pistons, Oil Pan; Measuring The Piston Diameter; Measuring The Clearance Between The Piston Ring And The Ring Groove; Measuring The Piston Ring Gap - Mitsubishi diesel engines Service Manual

3. Cylinder Block, Crankshaft, Pistons, Oil Pan

3.1 Measuring the piston diameter

Using a micrometer, measure the piston diameter
across the piston skirt and squarely with the
piston pin, as illustrated.
If the measured value is less than the limit,
replace with a new part.
allowable variation in weight among the pistons
on the same engine is 5 grams (0.18 oz).
Nominal
value
78.00
STD
(3.07)
Piston 0.25 78.25
diameter OS (3.08)
0.50 78.50
OS (3.09)
Max. allowable variation in
weight among pistons on the
same engine:
3.2 Measuring the clearance between the
piston ring and the ring groove
(1) Measure the piston ring-to-groove clearance. If
the measured value exceeds the limit, replace the
piston ring.
Standard value
No. 1 ring 0.09 to 0.11 (0.0035 to 0.0043) 0.300 (0.012)
No. 2 ring 0.07 to 0.11 (0.0028 to 0.0043) 0.200 (0.008)
Oil ring 0.03 to 0.07 (0.0012 to 0.0028) 0.200 (0.008)
(2) With the new piston ring installed, measure the
ring-to-groove clearance again. If the measured
value still exceeds the limit, replace the piston.

3.3 Measuring the piston ring gap

Install the piston ring being measured into the
gauge or a new cylinder. Then, using a thickness
gauge, measure the piston ring gap.
measured value exceeds the limit, replace all
rings of the relevant piston as a set.
STD=78
Gauge bore size 25 OS=78.25
50 OS=78.50
Note: To install a piston ring into the gauge, use a
piston to push the ring evenly.
Piston No. 1 ring 0.15 to 0.30 (0.006 to 0.012)
ring No. 2 ring 0.15 to 0.35 (0.006 to 0.014)
gap
Oil ring 0.20 to 0.40 (0.008 to 0.016)
ENGINE MAIN PARTS - INSPECTION AND CORRECTION
The maximum
Unit: mm (in.)
Standard
value
77.93 to 77.95
(3.070 to 3.071) (3.065)
78.18 to 78.20
(3.080 to 3.081) (3.075)
78.43 to 78.45
(3.090 to 3.090) (3.085)
5 g (0.18 oz)
or less
Unit: mm (in.)
Limit
+0.03 +0.0012
mm (3.07 in.)
0 0
+0.03 +0.0012
mm (3.08
0 0
+0.03 +0.0012
mm (3.09
0 0
Unit: mm (in.)
Standard value
(0.06)
Limit
Measuring the piston diameter
77.80
78.05
78.30
• \
No. 1 piston
ring-to-groove
clearance
Measuring the piston ring-to-groove clearance
Thickness gauge
If the
in.)
in.)
Measuring the piston ring gap
Limit
1.50
Measure squarely
with piston pin
Measuring location
No. 2 piston
ring-to-groove
clearance
2 - 27