I don't want anything that will need work or need to be OH'd anytime soon... let's say less than 900 SMOH.
Don't take the SMOH number as any kind of gospel. I'm currently overhauling a 200 SMOH engine that only had a year of flying on it. The aircraft I'm flying is 1600 SMOH and will likely run another 800. Since I fly it around 100 hours a year, that's a lot of time left.
Check compressions, idle oil pressure, and cam lift. Pull and inspect the plugs. Look at the accessories. Read through the engine AND propeller log to see how things match up. Borescope the cylinders. Find the overhaul entry to see which parts were new and which were serviceable.
Remember, the TBO number is a recommendation, not a requirement. If the engine is at or over TBO but still looks good, then keep flying it. If the engine is way below TBO but seems suspicious, then tear it down.
By the way, if you think any aircraft doesn't need any work at the time of purchase don't worry, it soon will. "Affordable" and "aircraft" don't usually fit together in the same sentence. ;-)
