2001 Yamaha YFM660 Raptor Factory Service Manual, Page 211Get this manual
VALVES AND VALVE SPRINGS 3.Install: Valve cotters
NOTE: Install the valve cotters while compressing the valve spring with the valve spring compressor and attachment 2Valve spring compressor: PNYM-04019, 90890-04019 Valve spring compressor attachment: PN90890-01243