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Can you check your model number again. Every combination that I put in for it does not come up.
I am pretty sure I know what your problem is though. The larger gear is held in place by a woodruff key, or a half moon key. It sits in the axle and keys to a slot in that large gear. If you can slide the gear to the side (it may be help in place by an E-clip or roll pin) you will see what I am talking about. The bad news is that snapper uses a very specialized key that must be bought from a snapper dealer. The good news is that they are fairly inexpensive. It is just a hassle sometimes to get to a dealer.