Piston And Connecting Rod - Inspect And Repair; Piston - Inspect Visually; Piston Outside Diameter - Measure; Piston Ring Groove - Inspect - Mitsubishi S12A2 Service Manual

4. Piston and Connecting Rod - Inspect and Repair

4.1 Piston - Inspect Visually

Check the combustion surface, piston pin bore, ring groove,
sliding surface and bottom surface of piston. If any defect
are found, replace the piston with a new one.

4.2 Piston Weight

Check the piston weight on the top face of piston.
When replacing pistons, be sure that the weight difference
per engine is within permissible range.
Item Part No. ID stamp
32517-91101 91101
Piston
32617-00701 00701
weight
differ-
32517-91201 91201
ence
32617-00600 00600

4.3 Piston Outside Diameter - Measure

Measure the piston outside diameter of piston skirt at right
angle to piston pin.If the value exceeds the limit, replace the
piston with a new one.
Nominal
Item
value
Piston outside ø150 mm
diameter [5.9 in.]

4.4 Piston Ring Groove - Inspect

Remove carbon deposits from piston and inspect the
entire circumference of piston.
(1) Remove all deposits such as carbon from each ring
groove.
(2) Visually check each ring groove for wear or damage. If
faulty, replace the piston with a new one.Inspect the
ring insert of No. 1 compression ring groove by dye
penetration test for cracks and separation.
Chapter 6 INSPECTION AND REPAIR OF BASIC ENGINE
Com-
pres-
Standard value
sion
ratio
14
Within ±15 g
[0.53 oz]
15
14
Within 20 g
[0.71 oz]
15
Standard
Limit value
value
149.71 to
149.75 mm 149.68 mm
[5.8941 to [5.8929 in.]
5.8957 in.]
Piston - Inspect Visually
Piston weight mark
Part number (last 5 digits)
Piston weight punch mark
Piston Outside Diameter - Measure
Ring carrier
Piston Ring Groove - Inspect
Engine front
direction mark
[F]
Measurement
point
No.1 compression ring
groove
No.2 compression ring
groove
Oil ring groove
6-15