You may not be able to get to the tensioning screw Joe mentions. Using a torch, or heat gun on the 1500 watt setting, put some heat at the arrow. This will expand the aluminum. At the same time try moving the timer back and forth to free it. Wiggel it off before it cools down. Might need gloves.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.
