Yamaha YZF-R15, Service Manual

Page: 179 / 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.
NOTE:
There should be no leakage at the valve seat “1”.
2. Remove:
• Valve cotters “1”
NOTE:
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
2
1
3. Remove:
• Upper spring seat “1”
• Valve spring “2”
• Valve “3”
• Valve stem seal “4”
• Lower spring seat “5”
NOTE:
Identify the position of each part very carefully so
that it can be reinstalled in its original place.
ssssssssssssssssssssssssss
ssssssssssssssssssssssssss
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.
• 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.
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
ssssssssssssssssssssssssss
ssssssssssssssssssssssssss