Yamaha XN125 2000, Service Manual

Page: 115 / 259

ENG
4-19
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and valve
seat are evenly polished, then clean off all of
the lapping compound.
NOTE:
For the best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between 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 Mechanic’s blueing dye (Dykem) 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 c again. If the
valve seat width is out of specification, reface
and lap the valve seat.
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EAS00241
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.
Valve spring free length (intake
and exhaust)
Valve spring
41.94 mm
<Limit>: 39.84mm
2. Measure:
• compressed valve spring force a
Out of specification
→
Replace the valve
spring.
b Installed length
VALVES AND VALVE SPRINGS