2010 Polaris Sportsman 850 Service Manual, Page 128Get this manual
ENGINE Valve Inspection
12Remove all carbon from valves with soft wire wheel or brushCheck valve face for runout, pitting, and burnt spotsTo check for bent valve stems, mount valve in drill or use "V" blocks and dial indicator5Measure diameter of valve stem with micrometer in three places, then rotate 90 degrees and measure again (six measurements total)Compare to specifications
Measure valve stem in several placesRotate the valve 90 degrees and measure for wear