There is a special tool required to change a mainspring, called a mainspring let down key set. This tool eliminates the possibility of the repairman getting injured and is described in the Clock Help pages. You really do not want to get whacked by a mainspring, they can hurt. This is why the tension of the spring is released before separating the clock plates, or attempting to remove the spring in anyway. Without the tension of the spring being released, the spring will unwind it self very fast in a uncontrollable fashion that can harm the repair person and the rest of the clock movement.