2001 Yamaha YFM660 Raptor Factory Service Manual, Page 215Get this manual
CYLINDER AND PISTON
CHECKING THE PISTON RING 1.Measure: Ring side clearance Use feeler gaugeOut of specification Replace the piston and rings as setNOTE: Clean carbon from the piston ring grooves and rings before measuring the side clearanceSide clearance Standard Top ring 2nd ring 0.040.08 mm (0.00160.0031 in) 0.030.07 mm (0.00120.0028 in) Limit 0.13 mm (0.0051 in) 0.13 mm (0.0051 in)
2.Position: Piston ring (in cylinder) NOTE: Insert ring into the cylinder and push it approximately 50 mm (2.0 in) into the cylinderPush the ring with the piston crown so that the ring will be at right angle to the cylinder borea 50 mm (2.0 in)