I own and fly a 67 172H 220 HP CSP, 760 hours or so to date, I use it for X country and back country, the Franklin 220 makes a 172 preform as good as or better than a 182 or a 172 XP. In my opinion, here are things that you need to consider to make a solid decision.
1. When was the engine installed, how many hours TT. , which STC do you have? Oil cooler under engine the original Franklin, oil cooler on top is the later one that I believe was developed for the PZL engine, the PZL has a deeper oil pan. Is it a Franklin or PZL?
2. How many times has it been rebuilt and by whom?
3. Do you have a mechanic that has worked on Franklins?
4. Does it have a good cam in it? There has been a common mistake made by rebuilders for years on many engines with respect to the cam to lifter interface, this is the reason Franklin camshafts are so scarce and failures are common. Search the back country pilot data base for a post I wrote “why some cams fail” It will explain it all.
5. Consider parts availability, many parts are scarce for these engines, cams, valves, cylinders, etc. As in all aviation if you look long and hard enough you will eventually find your parts. Beware of counterfeit parts! Valves and valve springs.
6. What prop is on it? There are no parts available for a MC 21, I got a field approval for a C201 for mine. Good luck on that.
7. I HIGHLEY!! Recommend an engine analyzer, Franklin 220 is a 10:1 compression engine, they are great, but they are also less tolerant than a 7:1 engine don’t EVEN think about running Mogas in this engine. I have a JPI 711 I love it as I do my 496, money well spent, can’t imagine not having it, The 711 takes away the boogey man, I know what all cylinder temps are, and flashing display limits without it you’re only guessing.
8. Definitely consider a sportsman STOL kit. It took 10-15 mph off all lower numbers, the airplane handles better under all conditions ,VX changed dramatically, My airport manager calls it the 172 that thinks it’s a helicopter and no change in cruise speed, I live in the mountains, 15 mph X winds are common, safer airplane all around, money well spent
9. I’m not trying to talk you out of buying one, I love mine, it’s fast and economical , running lean of peek on some cylinders @ 2500-2550 FL 8500 I average point to point less than 9 GPH @ 142-145 MPH @ 10 GPH it’s around 152 MPH not bad for an old 172. If you end up with it and need help sorting it out call me C-760-832-2736 Joe Good Luck