2001 Yamaha YFM660 Raptor Factory Service Manual, Page 210Get this manual
VALVES AND VALVE SPRINGS
11.Measure: Compressed spring force Out of specification Replaceb Installed length
Compressed spring force: Inner: 149173 at 27.2 mm (15.1917.64 kg, 33.5038.89 lb at 1.07 in) Outer: 165191 at 30.7 mm (16.8319.49 kg, 37.0942.94 lb at 1.21 in)