Suzuki GN125F Service Manual page 49

Decarbonize the piston.
Using a soft-metal scrapper or discarded piston ring
to decarbon the ring grooves of the piston. Do not use
the steel brush or the piston will be scratched.
INSPECTION
Temporary install the piston rings to the suitable position
with marked side upward.
Measure the clearance between the piston ring and groove
with a thickness gauge.
Piston ring-groove clearance limit:
1st: 0.180 mm
09900-20803: Thickness gauge
Measure the piston outside diameter at the place 8mm from
the skirt end with a micrometer.
Piston outside diameter limit:
56.844 mm at the 8 mm from the skirt end
09900-20203: Micrometer (50~75 mm)
Using a caliper gauge to measure the inside diameter of the
piston pin bore.
Piston pin bore inside diameter limit: 14.03 mm
09900-20605: Caliper gauge
Using a micrometer to measure the piston pin O.D..
Piston pin O.D.: limit: 13.98 mm
09900-20205: Micrometer (0-25)
2nd: 0.150 mm
ENGINE
3-18
8mm