I feel I'll probably euthanize a good engine when the time comes, so if I'm still running good when it's delivered, I have 90 days to return the core and I'll use up every minute of that!
Then I get to fly 200 hours not trusting my engine.
I unfortunately did this 2 years ago. Sent back a good running 0-320 H2AD motor within 90 days to Lycoming as my core. I waited until the last minute to swap it in.
I started flying a H2AD motor at 1416 hrs that was original from 1981 in April 2018. It was in a 1980 N 172 that got a new cam and lifters in 1981-82. No indication that the T mode was done then.
I flew it nervously for a friend at first for about 150 hrs after it mostly sat for 10 years. (9 hrs use in 10 years). I bought it from my friend after 150 hrs of flight time.
All was well for the most part with good oil analysis. At 1750 hrs We pulled all 4 clys off of it because of increased oil usage and lower leak down readings on 2 clys as I leaked it often. It was almost 40 years old. I found corrosion on the cam and lifters but no spauling. I did find 3 pistons with the ring gaps lined up with one another. Everything else looked good, could still see the cross hatch on the cyl walls.
Wasn't sure about the cam at the time, so I ordered a rebuilt zero time H2AD replacement from Lycoming in late Dec 2019 They said 7-9 weeks delivery. I figured it would take longer because of covid. It took 12 weeks to get it.
So I spaced out the original rings and put it back together so I could continue to fly it while I waited for the rebuilt motor. It only got new o rings for the clys bases and new valve cover gaskets.
It ran great after putting it back together. Leak down was better and the big thing was the oil usage went from 1 QT oil per 4 hours to 1qt per 8-9 hours! Huge improvement, I flew it for another 100 hrs until I had to swap in the new rebuilt motor. I definitely experienced buyers remorse by ordering the replacement motor. My old motor would have run for another 1000 hrs I would bet.
I swapped the motors July 4th weekend 2020 and just flew it to 400 hours yesterday. Way past the 200 hrs window that they say it could fail. The lycoming rebuilt motor is burning 1qt per 12-14 hrs and runs great with a power flow exhaust, challenger air filter, mapleleaf exhaust fairing which was on my old motor also. Hopefully myself or someone else will fly it to 2500 hrs or so before it needs to be overhauled or replaced. Did not want a 180 hp 360 or a STC to put in a D2J motor in or the added expense and time. I wanted cheaper and faster when I swapped motors which only took a week to swap since I didn't have change stuff like you would otherwise. So far it is working out good. That's my story.
Cold this Dec day.
6 months later swapping in the new motor. Hot as hell this July day. Cruiser fly's with me and spends most his time with me at the hanger, he has well over 500 hours I would bet.