Yamaha YFM4FAR Service Manual page 152

CAMSHAFT, ROCKER ARMS AND VALVES
3.Check:
Valve face
G
Pitting/wear → Grind the face.
Valve stem end
G
Mushroom shape or diameter larger than the
body of the stem → Replace.
4.Measure:
Margin thickness a
G
Out of specification → Replace.
Margin thickness:
Intake:
1.0 ~ 1.4 mm (0.0394 ~ 0.0551 in)
Exhaust:
0.8 ~ 1.2 mm (0.0315 ~ 0.0472 in)
5.Measure:
Runout (valve stem)
G
Out of specification → Replace.
Runout limit:
0.01 mm (0.0004 in)
NOTE:
When installing a new valve, always replace
G
the guide.
When a valve is removed or replaced,
G
always replace the oil seal.
6.Eliminate:
Carbon deposits
G
(from the valve face and valve seat)
7.Check:
Valve seat
G
Pitting/wear → Reface the valve seat.
8.Measure:
Valve seat width a
G
Out of specification → Reface the valve seat.
Valve seat width:
Intake:
1.2 ~ 1.4 mm (0.0472 ~ 0.0551 in)
<Limit>: 1.6 mm (0.0630 in)
Exhaust:
1.2 ~ 1.4 mm (0.0472 ~ 0.0551 in)
<Limit>: 1.6 mm (0.0630 in)
4 - 22
ENG