Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Has anyone else had the hairpin in the pinion shaft located on the lower left side of the machine break?  I understand that it keeps the pinion from turning, but what is the pinion doing that it shouldn't turn.  It snapped off in below zero weather one day when I was rolling it out of the garage.  Can any harm come from not having the pin preventing the pinion from turning?  I emailed Ariens about the pinion anti rotation kit, and they said if I lost the pin I should call the dealer.  Yeah, and have them tie up the machine for weeks on end.  I just stuck something else in to prevent it from spinning.  Can anyone explain the operation of the pinion and what it is doing?