So O360 cracked where? It is pretty common to have a case crack in internal webs. It is also common to have them repaired. I assume this is external and possibly not where they can do a weld repair? You can buy a new case half or halves for way less than a whole new engine. I assume the entire engine is OK, crank, rods, pistons, rings, valves, heads. If this were PRE 2019 when new engines were less it would be a tough choice. How?
If you have your heart set on a $40,000 new engine (vs repairing your existing engine for say $10,000), go for it. I see on ebay newly refurbished yellow tag Lycoming case halves ready to go for $6000.
If the case can be weld repaired, often they are, it would be sent out to a certified repair station, who will clean, inspected for all specs, weld, normalized (heat treat the case to alleviate residual stresses from welding); then it will be refinished, painted like new. put the crank and rods in, bolt the case halves together, put the jugs on. Not brain surgery.
So what are you worried about besides your wallet, Liability with your insurance company. Good on you for having hull insurance. If you repaired this engine you will have yellow tag from repair station for repaired / overhauled case and the A&P signed off log book for tear down engine and reassemble. I am not sure you even need an A&P but I would enlist one to help. You should be covered. This is experimental. We do not have to comply with the same type certificated airplane requirements. We don't have a type certificate therefore we don't need type certificate parts or need to maintain it to the same standard. That is why there is a placard warning in cockpit, can't be used for hire, etc. I think it wise to try and maintain it to same level or standards are type cert. planes but legally no, not required. As far as insurance.... you need to research that with the insurance company based on your policy.
Stuff happens. That is what insurance is for. If you are concerned CALL your insurance company and say I am doing XYZ to repair my engine. I doubt a new engine is required per your policy. Get your policy out and READ IT forwards and backwards like a lawyer. Then ask your insurance agent a lot of questions, like WHAT would void my policy so you would not pay out a claim... with typical examples.
Once repairs are done send them copies of the yellow tags and engine log book pages. Let's for example God forbid you screw up a landing, go off the side of the runway. I doubt they will not pay out because of unrelated engine case weld repair work. Now if you are not current, 90 days T/L's, Flight Review, Medical, and plane is out of "annual" or condition inspection, insurance may say "no bueno", not settle for damage or loss of aircraft loss, or any liability / medical claim per policy. Look at exclusions and disclaimers. I am far from an insurance expert. I have had to fight with insurance over home owner insurance and storm damage.
It is experimental. You could DO ALL the work and sign it off yourself if you are the builder. If you are not the builder I still think you can do a majority of the work, at least remove engine, remove all the accessories, and reinstall it once engine is gone through. I did something like this with my used engine I bought for my project. I wanted to go through it, so I got an A&P involved with engine tear down, sending items off to repair station for overall. He helped me reassemble engine. It was fun and learned a lot.
Even with a certified plane, with A&P supervision you can work on the plane.
