Installing a new rotor last week, couldn't hold the crank to tighten the nut to spec by putting it in gear and stepping down hard on the rear brake. I had this old oil filter wrench that fit the rotor circumference perfectly - it's about 3 1/2 inch diameter or a bit more when opened up and works with any 1/4 inch drive. It held that rotor perfectly while I tightened up the nut with my other hand on the torque wrench. It might be a way to loosen/tighten the clutch nut when engine's out of bike.