Use a vernier caliper at several points around the piston.
Piston Ring Groove Width Standard:
Top [A] 0.82 
0.84 mm (0.0323
0.0331 in.)
Second [B] 0.82 
0.84 mm
(0.0323 
0.0331 in.)
Service Limit:
0.92 mm (0.036 in.)
Second 0.92 mm (0.036 in.)
If the width of any of the two grooves is wider than the service limit at any point, replace the piston.
Piston Ring, Piston Ring Groove Wear Inspection
Piston Ring Thickness InspectionFuel Pump Removal
WARNINGGasoline is extremely flammable and can be
explosive
under certain conditions, creating the
potential for serious burns. Make sure the area is
well-ventilated and free from any source of flame
or sparks; this includes any appliance with a pilot
light. Do not smoke. T ...
Piston Wear Inspection
Measure the outside diameter [A] of each piston 5 mm
(0.20 in.) [B] up from the bottom of the piston at a right
angle to the direction of the piston pin.
If the measurement is under service limit, replace the piston.
Piston Diameter
Standard: 75.959 75.974 mm
(2.9905 2.9911 in.)
...
Before Servicing
Before starting to perform an inspection service or carry out a disassembly
and reassembly operation
on a motorcycle, read the precautions given below. To facilitate actual
operations, notes, illustrations,
photographs, cautions, and detailed descriptions have been included in each
chapter w ...