2001-2005 Honda TRX250EX Sportrax TRX250EX Factory Service Manual, Page 103Get this manual
CYLINDER HEADVALVE
CYLINDER HEAD ASSEMBLY
Blow through the oil passage in the cylinder head with compressed airInstall the valve spring seatsInstall new stem sealsLubricate the valve stem sliding surface ith molybdenum oil solutionInsert the valve into the guide while turning it slowly