2001 Yamaha YFM660 Raptor Factory Service Manual, Page 214Get this manual
CYLINDER AND PISTON
NOTE: Measure cylinder bore "C" in parallel to and at right angles to the cylinder matching surfaceThen, find the average of the measurementsStandard Cylinder bore "C" Wear limit
100.005100.100 mm 100.045 mm (3.9404 in) (3.93723.9388 in)X+Y 2
out of specification, rebore or replace the cylinder, and replace the piston and piston rings as set2nd step: Measure piston skirt diameter "P" with micrometerb 5.0 mm (0.20 in) from the piston bottom edge