2009 Suzuki 400 LTZ Quad Sport Service Manual, Page 177Get this manual
1D-35 Engine Mechanical: 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 tool (A): 0990020101 (Vernier calipers (115 mm, 150 mm)) Valve spring free length (IN& EX Service limit: 38.8 mm (1.53 in) Valve spring tension (IN& EX Standard: 182 210 (18.6 21.4 kgf, 41.0 47.2 Ibs)31.5 mm (1.24 in) I933H1140136-01
Valve seat width 1) Visually check for valve seat width on each valve faceIf the valve face has worn abnormally, replace the valve2) Coat the valve seat with red lead (Prussian Blue) and set the valve in place3) Rotate the valve with light pressureSpecial tool (A): 0991610911 (Valve lapper set)