Yamaha XC125 Service Manual page 51

INSPECTION AND REPAIR JENGI ___
• Valve seat is too narrow and right up near
[]
Ij
__.__j,j_x_ vaive margin (see "_1" diagram).
I Valve Seat Cutter Set Desired Result
30 ° cutter, first To center the seat and
Use to achieveits width of
45° cutter 1.0 mm (0.039 in)
I i= Valve seat is too narrow and is located
down near the bottom edge of "the valve
face (see diagram "[] ").
[]
I Valve Seat Cutter Set Desired Result
I 60 ° first To center the seat and
cutter,
Use to achieve its width of
45 ° cutter 1.0 mm (0.039 in)
Valve/Valve Seat Assembly Lapping _-_
1. Apply:
e Coarse lapping compound (_) (Small
amount)
"_ (to valve face)
o Molybdenum disulfide oil
(_ (to valve stem)
Be sure no compound enters into the gap
between the valve stem and guide.
2. Insert:
® Valves
(to cylinder head)
3. Rotate:
• Valve
Turn until valve and valve seat are evenly
polished, then clean off all compound.
NOTE:
To obtain the best lapping results, lightly tap
the valve seat while rotating the valve back and
forth between your hands.
4. Apply:
o Fine lapping compound (Small amount)
(to valve face)
3-12