2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 32Get this manual
MAINTENANCE Exhaust Valve Clearance 1Insert .006" (15 mm) feeler gauge(s) between end of exhaust valve stem and adjuster screw(s)Sportsman 400 H.OTiming Inspection Plug Gasket
Gasket Recoil Housing Feeler Gauge for Both Valves Drain Plug
Compression and Leakdown Tests