1999-2004 Honda TRX400EX FourTrax Service Manual, Page 105Get this manual
CYLINDER HEADVALVE Make tensioner shaft stopper tool of thin piece of steel (0.8 thick) using the diagram
Turn the tensioner shaft clockwise with the stopper tool to retract the tensioner, then insert the stopper fully to hold the tensioner in the fully retracted position
Install new gasket onto the cam chain tensioner lifterInstall the tensioner lifter onto the cylinder and tighten the two mounting bolt securelyRemove the stopper tool from the tensioner lifterCoat new O-ring with oil and install it into the tensioner lifter grooveInstall and tighten the tensioner lifter plug