I\'ve found a bug that sometimes causes the decoupler to break the engine off. I think this has something to do with the increased ejection force when an engine is inside. I\'ll look into it and try to make a fixed version. EDIT: After some testing, it looks like the configuration I have in the pictures works, but if I add another fuel tank on the bottom stage, it will rip the engine off when ejected. Right now I haven\'t been able to pinpoint the cause so all I can say is keep the lower stage small.