The Great Clock is wound three times a week. First, the auto-winding mechanism is set. This winds the striking train and the chiming train. Then the winding handle is attached to the going train. This part of the mechanism must be wound by hand. When the winding handle is operated, 'maintaining power' is activated. This keeps the Great Clock going while winding takes place. Oiling the mechanism is part of the clock's regular maintenance to keep all its parts in working order.
For more information about Big Ben visit:
http://www.parliament.uk/bigben
