Yamaha YFM250RX 2008 Service Manual page 142

VALVES AND VALVE SPRINGS
3. Measure:
• Valve seat width
Out of specification → Replace the cylinder
head.
a. Apply Mechanic's blueing dye (Dykem)
onto the valve face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
d. Measure the valve seat width.
NOTE: NOTE:
Where the valve seat and valve face contacted
one another, the blueing will have been
removed.
4. Lap:
• Valve face
• Valve seat
NOTE: NOTE:
After replacing the cylinder head or replacing
the valve and valve guide, the valve seat and
valve face should be lapped.
4-26
ENG
Valve seat width
Valve seat width C (intake)
0.90 ~ 1.10 mm
(0.0354 ~ 0.0433 in)
Valve seat width C (exhaust)
0.90 ~ 1.10 mm
(0.0354 ~ 0.0433 in)
Valve lapper
90890-04101
Valve lapping tool
YM-A8998