I've been told I need an airgun, but I have no means of getting one. An alternative is a tool that looks like this. It has a handle of flat steel that splits into a wide U, almost Y shaped but the V part of the Y is a U. At the end of each side of the U is a pin, and a pulley has a hole on either side of it's main nut, so when you put this thing on the pulley, you can hold it to stop it turning while you loosed or tighten the main axle nut of the pulley.
Does anyone know what this thing is called?