The 1800 hour overhaul time on the O-200 (and similar for nearly all other such engines) is a manufacturer's recommended interval. In Canada, and other placed I'm sure, it is only mandatory for commercially operated engines. Private aircraft can operate "on condition". My O-200 went happily to more than 3600 hours (with some interm cylinder work). At that point, I opened it up because I found some ferrous metal in the filter, the source of which could not be confirmed. It turned out that the engine was magnificent inside, and it was only a crimped on cover on the alternator drive making the metel (which really had nothing whatever to do with the critical internal workings of the engine). If taken care of, those engines have an amazing life span, because, yes, run properly, they really don't work that hard compared to a modern car engine!
Pilot DAR