If the engine mount screws are coming loose it may be due to unwanted vibration, possibly caused to unbalanced prop. Balanced props are highly recommended. Thread locker is also a good idea as gus pointed out.
I would like to say I have read article about using the prop to help balance the engine, but the engines they were referring to were the old cast-iron cylinder engines like the old Fox, todays engines are much more precise and don't really apply here. FWIW