2003 Polaris ATV Trail Boss 330 Factory Service Manual, Page 62Get this manual
ENGINE 5Remove valve sealsCAUTION: Replace seals whenever the cylinder head is disassembledHardened, cracked or worn valve seals will cause excessive oil consumption and carbon buildup
VALVE INSPECTION
1Remove all carbon from valve with soft wire wheel2Check valve face for runout, pitting, and burnt spotsTo check for bent valve stems, mount valve in drill or use "V" blocks and dial indicator
4Inspect split keeper groove for wear or flaring of the keeper seat area (B)NOTE: The valves cannot be re-faced or end groundThey must be replaced if worn, bent, or damaged5Measure diameter of valve stem with micrometer in three places and in two different directions (six measurements total)Compare to specifications