Type in Troy-Built tillers and you will find a ton of stuff about them. I have 6 horses and a tuffy, most have had the engines replaced before I got them. I have rebuilt some of the gearboxes because someone ran them without oil. Watch the seals in the tine shafts and wheel shafts, as they are notiorius for leaking bad, and are not easy to replace.
also watch the tine wear---after a certain point, ----they gotta be replaced with new ones.
When they work they are good tillers, just require a lot of care, which most of them never see by their owners!