82 kz 440 front sprocket

I just bought a 1982 kz 440ltd and I converted it from a belt drive to a chain drive, at first the front belt pulley would make a sound. Sounded like a playing card in bicycle spokes. After converting it to chain driven, I torqued the front sprocket nut to 70 ft pounds for a couple weeks no noise everything was fine. Recently I started to hear the same noise that I heard when I the pulley on. Does anyone know what could cause this or what should I do.

Is the front sprocket nut loose? Is the chain properly adjusted? Is the splined lock washer in place and properly installed?

The factory service manual says to torque the nut to 61 pound-feet, not 70.

See page 71.    www.kzrider.com/modules/ServiceManuals/kz440.pdf