2008 Suzuki LT-A400/F, LT-F400/F ATV Service Manual, Page 101Get this manual
Engine Mechanical: Valve Stem Wear If valve stem is worn down to the limit, as Measured with micrometerwhere the clearance is found to be in excess of the limit indicated replace the valve, if the stem is within the limit, then replace the guideAfter replacing valve or valve guide, be sure to re-check the clearanceSpecial tool0990020205 (Micrometer (0 25 mm)) Valve stem O.DStandard (IN: 4.975 4.990 mm (0.1959 0.1965 in) Standard (EX: 4.955 4.970 mm (0.1951 0.1957 in)
Valve Spring The force of the coil spring keeps the valve seat tightA weakened spring results in reduced engine power output and often accounts 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 spring does not fall within the specified range, replace the valve springSpecial tool0990020101 (Vernier calipers (115 mm, 150 mm)) Valve spring free length (IN& EX Service limit: 40.9 mm (1.61 in) Valve spring tension (IN& EX Approx196 (20.0 kgf, 44.1 lbs) at length 31.5 mm (1.24 in)