Yamaha TT-R125S Manuel D'atelier Du Proprietaire page 312

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VALVES AND VALVE SPRINGS
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3. Inspect:
Valve face
G
Pitting/wear → Grind the face.
Valve stem end
G
Mushroom shape or diameter larger
than the body of the stem → Replace.
4. Measure:
Margin thickness a
G
Out of specification → Replace.
Margin thickness:
Intake:
0.4 ~ 0.8 mm
(0.0157 ~ 0.0315 in)
Exhaust:
0.8 ~ 1.2 mm
(0.0315 ~ 0.0472 in)
5. Measure:
Runout (valve stem)
G
Out of specification → Replace.
Runout limit:
0.01 mm (0.0004 in)
NOTE:
When installing a new valve always replace
G
the guide.
If the valve is removed or replaced always
G
replace the oil seal.
6. Eliminate:
Carbon deposits
G
(from the valve face and valve seat)
7. Inspect:
Valve seats
G
Pitting/wear → Reface the valve seat.
ENG