Yamaha MBK MW125 2014, Service Manual

Page: 228 / 380

VALVES AND VALVE SPRINGS
5-25
NOTICE
ECA13790
Do not let the lapping compound enter the
gap between the valve stem and the valve
guide.
b. Apply molybdenum disulfide oil onto the
valve stem.
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and valve
seat are evenly polished, and then clean off
all of the lapping compound.
TIP
For the best lapping results, lightly tap the valve
seat while rotating the valve back and forth be-
tween your hands.
e. Apply a fine lapping compound to the valve
face and repeat the above steps.
f. After every lapping procedure, be sure to
clean off all of the lapping compound from the
valve face and valve seat.
g. Apply blue layout fluid “b” onto the valve face.
h. Install the valve into the cylinder head.
i. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
j. Measure the valve seat width again. If the
valve seat width is out of specification, reface
and lap the valve seat.
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EAS30286
CHECKING THE VALVE SPRINGS
The following procedure applies to all of the
valve springs.
1. Measure:
• Valve spring free length “a”
Out of specification
→
Replace the valve
spring.
2. Measure:
• Compressed valve spring force “a”
Out of specification
→
Replace the valve
spring.
Free length (intake)
33.75 mm (1.33 in)
Limit
33.40 mm (1.31 in)
Free length (exhaust)
33.75 mm (1.33 in)
Limit
33.40 mm (1.31 in)
Installed compression spring
force (intake)
132.20–152.20 N (13.48–15.52
kgf, 29.72–34.21 lbf)
Installed compression spring
force (exhaust)
132.20–152.20 N (13.48–15.52
kgf, 29.72–34.21 lbf)
Installed length (intake)
26.80 mm (1.06 in)
Installed length (exhaust)
26.80 mm (1.06 in)