Yamaha YZF-R15, Service Manual

Page: 180 / 338

5-17
VALVES AND VALVE SPRINGS
REMOVING THE VALVES
The following procedure applies to all of the
valves and related components.
NOTE:
Before removing the internal parts of the cylinder
head (e.g., valves, valve springs, valve seats),
make sure the valves properly seal.
1. Check:
• Valve sealing
Leakage at the valve seat → Check the valve
face, valve seat, and valve seat width.
Refer to “CHECKING THE VALVE SEATS ”
on page 5-19.
a. Pour a clean solvent “a” into the intake and
exhaust ports.
b. Check that the valves properly seal.
There should be no leakage at the valve seat “1”.
2. Remove:
• Valve cotters “1”
Remove the valve cotters by compressing the
valve spring with the valve spring compressor
and the valve spring compressor attachment“2”.
Valve spring compressor
YSST-603
3. Remove:
• Upper spring seat “1”
• Valve spring “2”
• Valve “3”
• Valve stem seal “4”
• Lower spring seat “5”
Identify the position of each part very carefully so
that it can be reinstalled in its original place.
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CHECKING THE VALVES AND VALVE
GUIDES
The following procedure applies to all of the
valves and valve guides.
1. Measure:
• Valve-stem-to-valve-guide clearance
Out of specification → Replace the cylinder
head
• Valve-stem-to-valve-guide clearance =
Valve guide inside diameter “a” -
Valve stem diameter “b”
Valve-stem-to-valve-guide clear-
ance (intake)
0.010–0.037 mm
Limit
0.080 mm
Valve-stem-to-valve-guide clear-
ance (exhaust)
0.025–0.052 mm
Limit
0.100 mm
Valve & Valve guide clearance = a–b
5-18
VALVES AND VALVE SPRINGS
2. Eliminate:
• Carbon deposits
(from the valve face and valve seat)
3. Check:
• Valve face
Pitting/wear → Grind the valve face.
• Valve stem end
Mushroom shape or diameter larger than the
body of the valve stem
→ Replace the valve.
4. Measure:
• Valve margin thickness D “a”
Out of specification → Replace the valve.
Valve margin thickness D (intake)
0.50–0.90 mm
Valve margin thickness D (ex-
haust)
0.50–0.90 mm
5. Measure:
• Valve stem runout
Out of specification → Replace the valve.
NOTE:
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always re-
place the valve stem seal.
Valve stem runout
0.010 mm
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 C “a”
Out of specification → Replace the cylinder
head.
a. Install the valve into the cylinder head.
b. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
c. Measure the valve seat width.
NOTE:
Where the valve seat and valve face contacted
one another, the blueing will have been re-
moved.
Valve seat width C (intake)
0.90–1.10 mm
Valve seat width C (exhaust)
0.90–1.10 mm
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