Yamaha WR400F(M) Owner's Service Manual page 336

VALVES AND VALVE SPRINGS
4. To secure the valve cotters onto the
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
5. Install:
NOTE:
Lubricate the valve lifters and pads with
molybdenum disulfide oil.
Valve lifter must turn smoothly when rotated
with a finger.
Be careful to reinstall valve lifters and pads
in their original place.
4 - 37
valve stem, lightly tap the valve tip with a
piece of wood.
Adjusting pad 1
Valve lifter 2
ENG