Checking The Valve Seats - Yamaha SR400 2014 Service Manual

EAS24300

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 width "a"
Out of specification  Replace the cylinder
head.
Valve seat width (intake)
1.30 mm (0.0512 in)
Limit
1.6 mm (0.06 in)
Valve seat width (exhaust)
1.30 mm (0.0512 in)
Limit
1.6 mm (0.06 in)
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a. Apply blue layout fluid "b" onto the valve face.
VALVES AND VALVE SPRINGS
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 width.
TIP
Where the valve seat and valve face contacted
one another, the blue layout fluid will have been
removed.
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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.
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a. Apply a coarse lapping compound "a" to the
valve face.
ECA13790
NOTICE
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, then clean off all of
the lapping compound.
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