2009 Polaris Sportsman 850 XP EFI EPS Service Manual, Page 153Get this manual
ENGINE Low Compression
No valve clearance Valve not seating properly (bent valve or carbondebris accumulated on sealing surface) Cylinder head gasket leak Cylinder or piston worn Piston rings worn, leaking, broken, or sticking Bent valve or stuck valve Valve spring broken or weak Rocker arm sticking