get a socket for it then put on the socket wrench and get a breaker bar for more leverage. From what I heard with a normal one it will take a breaker bar anyways. If that doesn't cover it someone has to have some air tools. BTW what are you doing so the sprocket doesn't rotate? Just don't leave it in gear as that may fuck up or chip your gears. Thats why I mentioned the 2x4 through the wheels so as the wheel rotates it will stop once the 2x4 is butted against the swing arm.

BTW most shops only charge like $25-35 to do the job for ya