Yamaha TTR125LM, Owner'S Service Manual

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4 - 28
ENG
VALVES AND VALVE SPRINGS
8. Measure:
●
Valve seat width
a
Out of specification
→
Reface the valve
seat.
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)
Measurement steps:
●
Apply Mechanic’s blueing dye (Dykem)
b
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. Where the
valve seat and valve face made contact,
blueing will have been removed.
●
If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat
must be refaced.
9. 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.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the valve
guide.