The Lycoming IO-360 in my 1976 Cardinal RG was overhauled in 1989. Since that time I've logged 2,440 hours on the engine. Lycoming recommends a TBO (time between overhauls) of 2,000 hours or 12 years, so the engine has performed much better than expected. The TBO is advisory, not mandatory (unless the airplane is used in revenue service under Part 135 or 121), so as long as the engine is performing as it should and the oil analyses and oil filter inspections aren't showing unusual levels of metal, there's no reason not to let the engine soldier on. The oil analyses have been very positive. In fact, the most recent one from Blackstone Labs concluded: "Nice report at 2,429 hours SMOH."