1999-2002 TRX400EX Fourtrax Service Manual, Page 101Get this manual
CYLINDER HEADVALVE
CYLINDER HEAD ASSEMBLYI INSTALLATION
_ SPRING COTTER
A-SPRING RETAINER _
Blow through the oil passage in the cylinder head with compressed airInstall the valve spring seatsInstall new stem sealsLubricate the valve stem sliding surface with molybdenum oil solutionInsert the valve into the guide while turning it slowly to avoid damage to the stem seal