Shibaura ST318, Workshop Manual

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39
4) Piston and piston ring
Disassembly
(1) Remove the piston ring using a piston ring tool.
(2) Remove the snap ring and extract the piston pin.
1. Piston ring
2. Piston pin
Inspection
(1) Piston
➀
Check the piston for crack, streak and burnout on
the outside surface and replace if remarkable.
➁
Measure the longer diameter at 10 mm above the
lower end of the piston skirt and bore of the
cylinder in the thrust direction, calculate the
clearance, and replace if the repair value is
exceeded.
➂
When the cylinder is substituted with an oversize
one, use a piston of an oversize.
Model Piston size Part code No.
Skirt bottom
longer dia.
S753
S.T.D 115317790 74.9325-74.9475
O.S. 0.5 115317800 75.4325-75.4475
O.S. 1.0 115317810 75.9325-75.9475
S773
S.T.D 115317630 76.9325-76.9475
O.S. 0.5 115317640 77.4325-77.4475
S773L
S.T.D.
115317990 76.9325-76.9475
O.S. 0.5 115317995 77.4325-77.4475
➃ Measure the piston pin hole diameter and piston pin
outside diameter and replace if the clearance
exceeds the service limit.
T120
Clearance between cylinder and piston (mm)
Model
Standard
assembling value
Service limit
S753
·
S773
·
S773L
0.0425 – 0.0765 More than 0.25
Piston skirt bottom longer dia. (mm)
Model
Standard
assembling value
Service limit
S753 ∅ 74.9325-74.9475 Less than ∅ 74.7
S773 ∅ 76.9325-76.9475 Less than ∅ 76.7
S773L ∅ 76.9325-76.9475 Less than ∅ 76.7
T121
T122
Clearance between piston pin hole and piston pin (mm)
Model
Standard
assembling value
Service limit
S753
·
S773
·
S773L
-0.004 ~ +0.004 More than 0.02