Yamaha RS90K Manuel D'atelier page 482

VALVES AND VALVE SPRINGS
9. Measure:
• Valve seat width a
Out of specification → Replace the cylinder
head.
Measurement steps:
• Apply Mechanic's blueing dye (Dykem) 1 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.
NOTE:
Where the valve seat and valve face contacted one
another, the blueing will have been removed.
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.
5-32
ENG
Valve seat width:
Intake:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.0630 in)
Exhaust:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
<Limit>: 1.6 mm (0.0630 in)