Yamaha FX Nytro 2008 Manuel D'atelier page 452

VALVES AND VALVE SPRINGS
10. Lap:
• Valve face
• Valve seat
NOTE:
After replacing the cylinder head or replacing the
valve and valve guide, the valve seat and valve
face should be lapped.
Lapping steps:
• Apply a coarse lapping compound a to the
valve face.
CAUTION:
Do not let the lapping compound enter the gap
between the valve stem and the valve guide.
• Apply molybdenum disulfide oil onto the valve
stem.
• Install the valve into the cylinder head.
• Turn the valve until the valve face and valve
seat are evenly polished, then clean off all of
the lapping compound.
NOTE:
For the best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
• Apply a fine lapping compound to the valve face
and repeat the above steps.
• After every lapping procedure, be sure to clean
off all of the lapping compound from the valve
face and valve seat.
• Apply Mechanic's blueing dye (Dykem) b onto
the valve face.
• Install the valve into the cylinder head.
• Press the valve through the valve guide and
onto the valve seat to make a clear impression.
• Measure the valve seat width c again. If the
valve seat width is out of specification, reface
and lap the valve seat.
5-35
ENG