Originally Posted by
sliderman
The missing tooth is the result of what's referred to as a single stress overload. It's the tooth that was in full contact at the instant the prop hit a solid object with the engine was at speed. A bad shim build will set the gears into a self destruct spiral. The top of the gears will be rounded and noticably worn. Your's should appear shiny with small nicks and dimples from chewing up that one tooth. Also, it sounds as though you are missing a locking ring that sits between the spanner nut and carrier. It has tabs that are to bend down and prevent the spanner from moving. No loc-tite is used.