well.......when i first got tower fun 51, i had this old O.S. .40 engine and it work great, never had any trouble with it. After a while, i decided to step up to more extreme stunts and need more power but ever since i bolted .46 ABC engine on it, it seemed not good engine for any reason and that engine is main cause of the crash. but now i fixed the fun 51 and has .50 O.S. and i didn't mind the little steep price tag and it works far better.
As someone mentioned, that old O.S. .40 was an ABC. Your new .50 is ringed
BUT it's an O.S.
In summary, two O.S. engines that ran great and one Tower engine that didn't. Not a lot of data to go on but I think you see a pattern beginning to form.
