If the measurement is under service limit, replace the piston.

Piston Diameter
Standard: 75.959
75.974 mm
(2.9905
2.9911 in.)
Service Limit: 75.81 mm (2.985 in.)
Cylinder (Upper Crankcase) Wear Inspection
Piston Ring, Piston Ring Groove Wear InspectionDrive Chain Removal/Installation
NOTE
Since the drive chain is installed through the swingarm,
The chain can not be removed other than by cutting it.
Prepare the new link pin, link plate, grease seals, and
tools for rejoining the chain.
Remove:
Bolts [A]
Front Footpeg Bracket [B]
Remove:
Bolts [A]
Chain Cover [B]
...
Engine Sprocket Installation
Replace the sprocket washer and axle cotter pin.
Install the engine sprocket onto the output shaft.
Apply molybdenum disulfide oil solution to the threads
and seating surface of the engine sprocket nut.
Tighten:
Torque - Engine Sprocket Nut: 145 N·m (14.8 kgf·m, 107
ft·lb)
NOTE
...
Tightening Sequence
Generally, when installing a part with several bolts, nuts,
or screws, start them all in their holes and tighten them to
a snug fit. Then tighten them according to the specified sequence
to prevent case warpage or deformation which can
lead to malfunction. Conversely when loosening the bolts,
n ...