Yamaha WR250F(N), Owner'S Service Manual

Page: 340 / 686

4 - 37
ENG
VALVES AND VALVE SPRINGS
5. Measure:
●
Runout (valve stem)
Out of specification
→
Replace.
NOTE:
●
When installing a new valve always replace
the guide.
●
If the valve is removed or replaced always
replace the oil seal.
6. Eliminate:
●
Carbon deposits
(from the valve face and valve seat)
7. Inspect:
●
Valve seat
Pitting/wear
→
Reface the valve seat.
Runout limit:
0.01 mm (0.0004 in)
8. Measure:
●
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.