Yamaha MT-09SP 2021 - Checking the Valve Seats

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VALVES AND VALVE SPRINGS
5. Measure:
• Valve stem runout
Out of specification → Replace the valve.
TIP
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always re-
place the valve stem seal.
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CHECKING THE VALVE SEATS
The following procedure applies to all of the
valves and valve seats.
1. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
2. Check:
• Valve seat
Pitting/wear → Replace the cylinder head.
3. Measure:
• Valve seat contact width “a”
Out of specification → Replace the cylinder
head.
a. Apply blue layout fluid “b” onto the valve
face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
d. Measure the valve seat contact width.
TIP
Where the valve seat and valve face contacted
one another, the blue layout fluid will have been
removed.
4. Lap:
• Valve face
• Valve seat
TIP
After replacing the cylinder head or replacing the
valve and valve guide, the valve seat and valve
face should be lapped.
a. Apply a coarse lapping compound “a” to the
valve face.
NOTICE
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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.
Valve stem runout
0.020 mm (0.0008 in)
Valve seat contact width limit
(intake)
1.6 mm (0.06 in)
Valve seat contact width limit
(exhaust)
1.8 mm (0.07 in)
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