Yamaha YBR250 2007 Service Manual page 215

VALVES AND VALVE SPRINGS
1
2. Replace:
• valve guide
NOTE:
To ease valve guide removal and installation, and
to maintain the correct fit, heat the cylinder head
to 100
a. Remove the valve guide with the valve guide
remover 1.
b. Install the new valve guide with the valve guide
installer 2.
c. After installing the valve guide, bore the valve
2
guide with the valve guide reamer 3 to obtain
the proper valve-stem-to-valve-guide
clearance.
NOTE:
After replacing the valve guide, reface the valve
seat.
3
3. Eliminate:
• carbon deposits
4. Check:
• valve face
• valve stem end
5. Measure:
a
• valve margin thickness a
5-25
o
C in an oven.
Valve guide remover (ø6)
90890-04064
Valve guide installer (ø6)
90890-04065
Valve guide reamer (ø6)
90890-04066
Pitting/Wear --> Grind the valve face.
Mushroom shape or diameter larger than the
body of the valve stem
--> Replace the valve.
Out of specification --> Replace the valve.
Valve margin thickness
0.80 ~ 1.20 mm (0.032 ~ 0.047 in)
ENG