Smoked outrunner questions

I was running a 600kv outrunner in my direct drive elst on 4cells. I put a 400kv motor in it and it also ran ok on 4 cell. I ran it on 6cell and thats when things went bad. It was better off the line but after about 75% throttle it would cut out and screech like a stuck rotor on start up. If Even if I tried to accelerate slowly it would still do it. After a few passes up and down the street smoke was pouring out of it. I unplugged the batteries and found the motor very hot. I pulled the motor out and it hardly turns at all now. Both bearings seem good, magnets are still good so what gives?

[brushlessboy16]

is it the 50-55?

umm is the outer can warped from the heat?
It might not be balaance well enough to run that many rpm

I run mine on 5s and its fine though..

could the shaft be bent?

both are 50-55's I used the shft out of the 600kv so I didn't have to cut the 400's. I put it back in 600 and its fine. I took all three bearings out of the 400 and they are good. I never tried 6cells with the 600kv motor. I did run the 600kv on 18 nimh cells without any problems other than weak start-up.