Yamaha RS90K Manuel D'atelier page 480

VALVES AND VALVE SPRINGS
• After installing the valve guide, bore the valve
guide with the valve guide reamer 3 to obtain
the proper valve-stem-to-valve-guide clearance.
NOTE:
After replacing the valve guide, reface the valve
seat.
3. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
4. Inspect:
• Valve face
Pitting/wear → Grind the valve face.
• Valve stem end
Mushroom shape or diameter larger than the
body of the valve stem → Replace the valve.
5. Measure:
• Valve margin thickness a
Out of specification → Replace the valve.
6. Measure:
• Valve stem runout
Out of specification → Replace the valve.
NOTE:
• When installing a new valve, always replace the
valve guide.
• If the valve is removed or replaced, always
replace the oil seal.
7. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
8. Inspect:
• Valve seat
Pitting/wear → Replace the cylinder head.
5-31
ENG
Valve guide remover (ø5):
90890-04097, YM-04097
Valve guide installer (ø5):
90890-04098, YM-04098
Valve guide reamer (ø5):
90890-04099, YM-04099
Valve margin thickness:
Intake:
0.8 ~ 1.2 mm (0.0315 ~ 0.0472 in)
Exhaust:
0.5 ~ 0.9 mm (0.0197 ~ 0.0354 in)
Valve stem runout:
0.01 mm (0.0004 in)