Sym Mio 50 Service Manual page 82

Use 60° cutter to cut a quarter lower parts out.
Remove the cutter and check new valve seat.
Use 45° cutter to grind the valve seat to specified
width.
Caution
Make sure that all roughness and uneven
faces had been grinded.
Grind valve seat again if necessary.
Coat the valve seat surface with red paint.
Install the valve through valve guide until the valve
contacting with valve seat, slightly press down the
valve but do not rotate it so that a seal track will be
created on contact surface.
Caution
The contact surfaces of valve and valve seat
are very important to the valve sealing
capacity.
If the contact surface is too high, grind the valve
seat with 32° cutter.
Then, grind the valve seat to specified width with
45° cutter.
If the contact surface is too low, grind the valve
seat with 60° cutter.
Then, grind the valve seat to specified width with
45° cutter.
To this chapter contents
Contact surface too high
Contact surface too low
6. Cylinder Head / Valve
Old valve seat width
60°
1.0mm
45°
Old valve seat width
Old valve seat width
32°
60°
6-13