Yamaha F400A 2022 - Checking the Valve Seat; Refacing the Valve Seat

Cylinder head
7-63
4. Measure:
• Inside diameter
Checking the valve seat
1. Remove:
• Carbon deposit
2. Measure:
• Valve seat contact width
Not seated properly/out of specification
→ Reface the valve seat.
Uneven → Check the valve guide.
a. Remove the carbon deposits from the
valve.
b. Apply a thin, even layer of blue layout
fluid (Dykem) onto the valve seat.
c. Press the valve lightly against the valve
seat using the special service tool “1”.
d. Measure the valve seat contact width
“a” where the blue layout fluid is ad-
hered to the valve face.
TIP:
Reface the valve seat if the valve is not seated
properly or if the valve seat contact width is
out of specification. Check the valve guide if
the valve seat contact width is uneven.
Refacing the valve seat
After every lapping procedure, make sure
to clean off any remaining lapping com-
pound from the cylinder head and valves.
Valve guide reamer “2”
90890-06804
Valve guide reamer “2”
YB-06804
Inside diameter IN
5.504–5.522 mm (0.2167–
0.2174 in)
Inside diameter EX
5.504–5.522 mm (0.2167–
0.2174 in)
Valve lapper “1”
90890-04101
Valve lapping tool “1”
YM-A8998
1
Seat contact width IN
1.10–1.40 mm (0.0433–0.0551
in)
Limit
1.850 mm (0.0728 in)
Seat contact width EX
1.40–1.70 mm (0.0551–0.0669
in)
Limit
2.150 mm (0.0846 in)
a