Yamaha YFM250XL(C) Service Manual page 122

ı
Ç
4
Î
INSPECTION AND REPAIR
ı Valve seat is in the middle of the valve face
but too narrow.
Valve seat cutter set
Use 45˚ cutter
Ç Valve seat is too narrow and right up near
valve margin.
Valve seat cutter set
30˚ cutter To center the seat
Use
45˚ cutter
Î Valve seat is too narrow and is located down
near the bottom edge of the valve face.
Valve seat cutter set
60˚ cut-
ter, first
Use
45˚ cutter
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5.Lap:
Valve face
Valve seat
NOTE:
After refacing the valve seat or replacing
the valve and valve guide, the valve seat
and valve face should be lapped.
*********************************
Valve lapping steps:
Apply a coarse lapping compound 1 to
the valve face.
CAUTION:
Be sure no compound enters the gap
between the valve stem and guide.
4 - 24
ENG
Desired result
To achieve a uni-
form valve seat
width of 1.0 mm
(0.04 in)
Desired result
and to achieve its
width of 1.0 mm
(0.04 in)
Desired result
To center the seat
and increase its
width.