Yamaha TTR90(M), Owner'S Service Manual

Page: 184 / 287

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ENG
VALVES AND VALVE SPRINGS
2. Lap:
●
Valve face
●
Valve seat
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
●
Apply a coarse lapping compound to the
valve face.
●
Apply molybdenum disulfide oil to 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 compound.
●
Apply a fine lapping compound to the
valve face and repeat the above steps.
●
Apply Mechanic’s blueing dye (Dykem) to
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
pattern.
●
Measure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
NOTE:
After every lapping operation be sure to
clean off all of the compound from the valve
face and valve seat.