Checking The Valve - Yamaha 2008 YZ250F Fahrer- Und Wartungshandbuch

REMOVING THE VALVE LIFTER
AND VALVE COTTER
1. Remove:
• Valve lifter "1"
• Pad "2"
Identify each lifter "1" and pad "2" po-
sition very carefully so that they can
be reinstalled in their original place.
2. Check:
• Valve sealing
Leakage at the valve seat
spect the valve face, valve seat
and valve seat width.
Checking steps:
a. Pour a clean solvent "1" into the
intake and exhaust ports.
b. Check that the valve seals prop-
erly.
There should be no leakage at the
valve seat "2".
3. Remove:
• Valve cotter
Attach a valve spring compressor "1"
between the valve spring retainer and
the cylinder head to remove the valve
cotters.
Valve spring compres-
sor:
YM-4019/90890-04019

CHECKING THE VALVE

1. Measure:
• Stem-to-guide clearance
Stem-to-guide clearance = valve
guide inside diameter "a" -
valve stem diameter "b"
Out of specification
the valve guide.
Clearance (stem to
guide):
Intake:
→
In-
0.010–0.037 mm
(0.0004–0.0015 in)
<Limit>:0.08 mm
(0.003 in)
Exhaust:
0.025–0.052 mm
(0.0010–0.0020 in)
<Limit>:0.10 mm
(0.004 in)
2. Replace:
• Valve guide
Replacement steps:
To ease guide removal, installation
and to maintain correct fit heat the
cylinder head in an over to 100 °C
(212 °F).
a. Remove the valve guide using a
valve guide remover "1".
VALVES AND VALVE SPRINGS
→
Replace
4-22
b. Install the new valve guide using a
valve guide remover "1" and valve
guide installer "2".
c. After installing the valve guide,
bore the valve guide using a valve
guide reamer "3" to obtain proper
stem-to-guide clearance.
Valve guide remover:
Intake:4.0 mm (0.16 in)
YM-4111/90890-04111
Exhaust:4.5 mm (0.18
in)
YM-4116/90890-04116
Valve guide installer:
Intake:4.0 mm (0.16 in)
YM-4112/90890-04112
Exhaust:4.5 mm (0.18
in)
YM-4117/90890-04117
Valve guide reamer:
Intake:4.0 mm (0.16 in)
YM-4113/90890-04113
Exhaust:4.5 mm (0.18
in)
YM-4118/90890-04118
After replacing the valve guide reface
the valve seat.
3. Inspect:
• Valve face
→
Pitting/wear Grind the face.
• Valve stem end
Mushroom shape or diameter
larger than the body of the stem
→
Replace.