I’m looking at a 310 with original 1970s engines that hit had a top overhaul done (Factory new cylinders) in 1998 at about 1400. The engines now have 220 hour since top overhaul. Compressions are all over the place, but it’s not the most reliable test so ignoring t.
My question is: is it standard practice to do a top overhaul instead of overhaul when the IO470s hit TBO? How many more hours can I expect to get out of these assuming they have been correctly broken in and maintained? Seller says another 1000 hours, but if that were the case I would expect to see many more high-hour top overhauled engines.
Many people will do top overhauls on 470s at TBO and keep on trucking. It’s not uncommon to see 470s at 2000-2500 SMOH, but the resale value is lower. Keep in mind that while compressions aren’t the most reliable indicator, they still have values they must be above to be airworthy. On original 1970s bottom ends, there is always a concern about age, corrosion, etc. If the price is right and the risk doesn’t bother you (it wouldn’t bother me), go for it.