2004-2009 Suzuki LT-Z250 Service Manual, Page 70Get this manual
VALVE SPRING The force of the coil spring keeps the valve seat tightWeakened spring result in reduced engine power output, and often account for the chattering noise coming from the valve mechanismCheck the valve springs for proper strength by measuring their free length and also by the force required to compress themIf the spring length is less than the service limit or if the force required to compress the valve spring is not within specification, replace both the inner and outer springs as set Valve spring free length (INEX) Service Limit: 43.0 mm (1.69 in) Valve spring tension (INEX) Standard: 256 29 N36.6 mm (26.1 30.0 kgf36.6 mm, 57.5 6.1 lbs1.44 in)09900-20101: Vernier calipers