Yamaha YZ450FX 2019, Owner'S Service Manual

Page: 224 / 388

VALVES AND VALVE SPRINGS
5-25
EAM30090
REMOVING THE VALVES
TIP
Before removing the internal parts of the cylinder
head (e.g., valves, valve springs, valve seats),
make sure that the valves are properly sealed.
1. Remove:
• Valve lifter “1”
•
Adjusting pad “2”
TIP
• Place a cloth in the timing chain space to pre-
vent adjusting pads from falling into the crank-
case.
•
Make a note of the positions of valve lifters and
adjusting pads so that they can be reinstalled
in their original places.
2. Check:
•
Valve sealing
Leakage at the valve seat

Check the valve
face, the valve seat, and the valve seat con-
tact width.
Refer to “CHECKING THE VALVE SEATS”
on page 5-27.
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a. Pour a clean solvent “a” into the intake and
exhaust ports.
b. Check that the valves are properly sealed.
TIP
Check that there are no kerosene leaks from the
valve seat “1”.
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3. Remove:
• Valve cotter “1”
TIP
Remove the valve cotters by compressing the
valve spring with the valve spring compressor
“2” and the valve spring compressor attachment
“3”.
4. Remove:
• Valve spring retainer “1”
•
Valve spring “2”
• Valve “3”
•
Valve stem seal “4”
• Valve spring seat “5”
TIP
Identify the position of each part very carefully so
Valve lapper (ø14)
90890-04101
Valve lapping tool (14mm)
YM-A8998
2
1
Valve spring compressor
90890-04019
Valve spring compressor
YM-04019
Valve spring compressor attach-
ment
90890-04108
Valve spring compressor adapter
22 mm
YM-04108
a
1
a
2 2
1 1
3 3