Yamaha YFM660FS Grizzly 4x4 Supplementary Service Manual page 244

VALVES AND VALVE SPRINGS
3.Install:
Valve cotters
G
NOTE:
Install the valve cotters while compressing the
valve spring with the valve spring compressor
1 and valve spring compressor attachment
2.
4.To secure the valve cotters onto the valve
stem, lightly tap the valve tip with a piece of
wood.
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
4 - 31
ENG
Valve spring compressor:
P/N. YM-04019, 90890-04019
Valve spring compressor
attachment:
P/N. 90890-01243