Hi folks, i have a little problem with my heli.

my friend crashed his bcx2 and boght a smaller and less complicated heli. he gave me his broken bcx2, i had to change the battery holdet, skids and the rear body. when i did all the pre-flight checks i found that the outer shaft is slightly out of round and the heli is shaking a little-bit. when i try to hover the heli takes off and stabilize in the air for 2 sec, then it start to spin clockwise, i tried to ajust the trim but at some point it spins clockwise, i give a tiny click of trim and the heli start to spin out conterclockwise... ive tried to ajust the"main motor proportional mix" and still the same thing but the trim "sensitive point" change location on the trim travel . any idea of what could be the problem ? could to a video of the shake and the problem on demand

thanks in advance folks