Use a scuff pad (320)and carb cleaner \\\ wear rubber gloves and protect your eyes with safty glasses and due it outside in the fresh air.
YOU WONT HURT THE PISTON THIS WAY :drinkers:
wire wheel on a bench grinder. I have 2 grinders stacked on a pedestal. 2 different stones on the bottom, a wire wheel on one side of the top and a buffing wheel on the other side. works pretty well and doesn't take up as much space that way.