A bit of help regarding maintenance

[Sam Buchanan]

It depends. For E-AB, for the most part, anything goes. You could power your plane with a twisted rubber band if you wanted to, and anybody can work on any engine. I believe you can get a shorter initial test period if you use a certified aircraft engine, if so then you need a licensed mechanic to work on the engine.

Just for clarification, the shorter Phase One test period (25 hrs vs 40 hrs) is available if the engine and prop were originally certificated as a combination. But even if that is the case, anyone can do any maintenance on the engine because there really isn't any such animal as a certificated engine in an aircraft with an experimental airworthiness certificate. An A&P is only needed for the logbook endorsement for the 12-month Condition Inspection.