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Note 2: The piston is barrel shaped. Do not use a standard micrometer to measure the diameter precisely.
Use a blade micrometer.
viii) Measure the inner diameter of the piston pin hole (Fig. 11) with an internal
caliper gauge.
Replace the piston in case the measured inner diameter is more than φ9.140mm.
Note: Measure the piston pin hole at both ends vertically and horizontally. Adopt
the largest as the data.
Viiii) Install the maintained piston ring (see 3. Inspection and maintenance of the
piston ring below) or a new piston ring in the piston ring groove and make sure it
moves smoothly in the groove.
③
Inspection and maintenance of the piston ring
Note: There is no top side and base side of the piston ring when it is new, but once it is used, surfaces of the
piston ring become matching to the top/base surface of the piston ring groove. So once top/base side is
decided, the top side should always be on top side and the base side always on base side. Do not install
the piston ring upside down when you use the same piston ring after maintenance.
i) Remove carbon buildup on the inner side of the piston ring with a tool made of softer material than the
piston ring itself not to give damage on it.
ii) Check the upper side of the piston ring for carbon buildup and remove the carbon buildup. Do not file off the
ring itself but only remove the carbon buildup.
iii) Check the outer surface of the ring for heat mark or any scratches. Replace the ring if there are damages
on it. Check the inner wall of the cylinder block for damage as well. It is likely to have damages on it when
the outer surface of the ring is damaged.
iv) Check the bottom side of the piston ring for heat mark or any scratches. Replace the ring if there are
damages on it. Check the base surface of the piston ring groove for damages as well. It is likely to have
damages on it when the bottom side of the piston ring is damaged.
④
Inspection and maintenance of the piston pin
i) Pull out the piston pin to remove carbon buildup.
ii) Measure the outer diameter of the piston pin, both ends, center vertically and
horizontally (total 6 points). Replace the piston pin in case the measured diameter is
less thanφ9.010mm. (Fig.12)
⑤
Inspection and maintenance of the crankshaft assembly
Note: The crankshaft assembly and connecting rods cannot be disassembled.
i) Wash the assembly unit with kerosene or gasoline.
WARNING
When you wash the part with gasoline or kerosene, carry out the work only outdoors or in well ventilated
area away from any source of fire to prevent a fire.
ii) Measure each diameter of the crankshaft shown in Fig.13 with a micrometer. Replace the crankshaft
assembly in case the measured diameter is less than the size shown in Fig.13.
Summary of Contents for GT120THU
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