2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 68Get this manual
ENGINE (300) Cylinder Head Assembly CAUTION
Wear eye protection during assemblyNOTE: Assemble the valves one at time to maintain proper order1Install new valve seals on valve guides786Place retainer on springs and install valve spring compressorCompress spring only enough to allow split keeper installation and prevent loss of spring tensionInstall split keepers with the gap even on both sidesRepeat procedure for remaining valveWhen all valves are installed, tap lightly with soft faced hammer on the end of the valves to seat the Split keepers
Valve Sealing Test
12Clean and dry the combustion chamber areaPour small amount of cleaning solvent into each port and check for leakage around each valveThe valve seats should hold fluid with no seepage
Engine Bottom End Disassembly