Yamaha RS90GTZ Service Manual page 261

VALVES AND VALVE SPRINGS
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
Out of specification → Replace the valve.
6. Measure:
• Valve stem runout
Out of specification → Replace the valve.
TIP
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always
replace the valve stem seal.
7. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
8. Inspect:
• Valve seat
Pitting/wear → Replace the cylinder head.
5-36
ENG
Valve margin thickness:
Intake:
0.80 ~ 1.20 mm
(0.0315 ~ 0.0472 in)
Exhaust:
0.50 ~ 0.90 mm
(0.0197 ~ 0.0354 in)
Valve stem runout:
0.010 mm (0.0004 in)