[florianz]

Are the magnets loose on the rotor, or is it just a bit damaged?
I had similar problems with my losi motor, and fixed it with good super glue.
Are the bearings damaged? If so, the rotor touches the inner of the motor.
Just soak the kevlar rovings with super glue, as long the magnets are not loose, that should be working.
try to get the Motor clean from dust and sand, that damages the rotor.