Here is where you can get your ??'s answered about troy bilt tillers, find service manuals, etc. The first models were made by Gateway and troy bilt bought them out.
They can tell you how to locate model numbers on the gearcase also.
I was flogging one of them old dogs awhile back and chzuck gave me lots of info. Some guys replace those engines with the HF $100 Predator engine with good results. Lots of parts on flea bay. (and lots are overpriced) Take pic's before you remove any tines, the tines have to be installed correctly or it won't dig dirt correctly and are a real puzzle even with pic's if you have a pile of tines. Mine had a big pile of tines that Bubba had removed when I started getting this one back together.
Don't overlook the 3rd link about manuals at the bottom of this post.
Good Luck with yours.
If you can find a guy in these forums by the name of chzuck (Dirt digger) he is a Troy bilt Tiller (Gateway )specialists. Just noticed he is in the 2nd link. He can give you links to download all kinds of Owners manuals and Service info about your old tiller once the correct name (Horse 1, 11, or 111, or Pony and model is ID'ed. If it's the older Gateway their owners manual has lots of good service info and how to safely use the tiller and also the Service manual gets into detail about the gearbox, etc. (Later model owners manuals for eq is usually not much for actual servicing in detail)
https://www.mytractorforum.com/forums/tiller-talk.214/
https://www.mytractorforum.com/threads/ ... t-12408045
https://www.mytractorforum.com/291-troy-bilt-tiller-manuals/