Recently converted t' 13mm power, went unstable off t' rod and tumbled.  Motor wasn't seated all t' way because I friction fit it and it got stuck. Avast! Blimey!  Couldn't get it in any further, couldn't get it out. Begad! Blimey!  I'll try again with t' engine seated properly t' see if it flies stable or if t' 13mm conversion makes it a shelf queen.