Yamaha TT-R125EY Service Manual page 121

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