Do you mean the rotor? Do not try to put it back on with the bolt, you could strip out the hole in the crank, then you would be screwed. If you can not get it off you have two choices, make a proper installer with a bolt (or threaded rod) that will fit and put it back on, then get an alternator kit, or loosen the motor mount so you can jack up the engine high enough to pull the rotor. In the latter case you will also have to pull the outdrive to re-align it, as the chances of getting the motor mounts back EXACTLY the same are slim.
