2001 Yamaha YFM660 Raptor Factory Service Manual, Page 229Get this manual
CHECKING THE CLUTCH SPRING The following procedure applies to all of the clutch springs1.Check: Clutch spring Damage Replace the clutch springs as set
2.Measure: Clutch spring free length Out of specification Replace the clutch springs as setClutch spring free length: 42.8 mm (1.69 in) Limit: 40.7 mm (1.60 in)