Yamaha TT-R125(R) Owner's Service Manual page 264

VALVES AND VALVE SPRINGS
8. Measure:
Measurement steps:
G
G
G
G
G
9. Lap:
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
G
Do not let the compound enter the gap
between the valve stem and the valve
guide.
G
4 - 28
Valve seat width a
G
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)
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.
Valve face
G
Valve seat
G
Apply a coarse lapping compound to the
valve face.
CAUTION:
Apply molybdenum disulfide oil to the
valve stem.
ENG