Onto more interesting things. Light knocking noise in the engine. I thought I'm going to have to take the head off. You can magically replace a valve with the head on, if it was as easy in real life
If you have stripped and rebuilt the Moths engine and don't get a completed message you probably missed the head gaskets.
You can remove the cylinders complete, what the game doesn't tell you is that it places them on the wooden palates where you can strip them more easily.
You can remove the heads while still on the plane but its a bit harder, the head gaskets are easy to miss.