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 InspectionExploded View
11. ZX1000JD/KD
AD: Apply adhesive.
AL: Tighten the two clamp bolts alternately two times to ensure even tightening
torque.
G: Apply grease.
L: Apply a non-permanent locking agent.
Specifications
...
Rocker Arm Installation
Install the both rocker arms [A] so that their marks [B] face
left side.
Replace the tie-rod nut, rear shock absorber nut and
rocker arm nut with new ones.
Apply grease to the inside of the oil seals.
Tighten:
Torque - Rocker Arm Nut: 34 N·m (3.5 kgf·m, 25 ft·lb)
Tie-Rod ...
Shift Fork Guide Pin/Drum Groove Wear Inspection
Measure the diameter of each shift fork guide pin [A], and
measure the width [B] of each shift drum groove.
If the guide pin on any shift fork is less than the service
limit, the fork must be replaced.
Shift Fork Guide Pin Diameter
Standard: 6.9 7.0 mm (0.272
0.276 in.)
Service Limit: ...