To remove the centre gear, you must first remove the timers face and hand, this can be done either by drilling the rivers on top, or using pliers to bend and pull the face off.

begin by removing the three rivets near the edge of the face, then either use pliers or by hand, you should pull the face off the last rivet, and the had with it.

once you have removed the face and hand, a small metal rod and brass band covering it should remain,(the metal rod is the top of the gear, being held by the brass band) using a thin metal pin and a mallet, you should be able to knock the rod out of the brass band, setting the centre gear free.