Hello everyone,
I searched a lot for it , still, don't want to experiment with my motors.
Actually, few days back some metal dust (that came out during drilling my motor mounts) got clinged to the magnet inside the motors. I understand that it was absolute carelessness from my side
Unknowingly , since, I took part in a competition held at IIT-K, I was finishing up my Quadcopter and so just to have a regular check of motor I gave some throttle(20%) after which the motor gave a noisy sound and some smoke was also seen although it rotated. Immediately I disconnected all my motors and on opening them I found a powdery substance clinged to the magnets. I'd tried my level best in cleaning it with a soft cloth but still, there is dust inside.
Kindly tell me some methods of removing that dust on magnets. I have 4 motors and same problem in all of them.
Please Please help me out. Otherwise new motors are damn expensive!!!

You will have to do it manually - there is no other way.

One thing you can do is mix up some epoxy and smear thinly
on the inside of the bell - that way most of the metal filings will
be trapped in the epoxy matrix and not foul when the motor is running.

Sir,
I'm ready to give every effort to clean it myself.
Planning to clean it with the ear buds(used for cleaning ears) and then I'll use blower end of vaccuum cleaner to remove every small strand of cotton(if any) in it.
Still, more suggestions/methods to do this are most welcome.

@utkarshg13
Try wrapping double side sticky tape around your chichi ungli,
And wipe the inside of the motor. Might work.

Nice idea
Will try that too...

More suggestions awaited!

smoke! that black soot could be sign of burnt motor / coils.
Only a more stronger magnet can remove metal filings from another magnet, else as others have suggested
use glue, epoxy, strong adhesive tape to wrap the core and hope they stick to 'em.

cheers.

Thanks.

Have you tried using hot glue or Fevicol? It should come of easily too, without dislocating the magnets. Or try using modelling clay.

Best idea so far!

Yes! Modelling clay (plasticine) 

Thank you so much everyone. 
I would try doing everything suggested above and would update my progress after then.

you get this stuff called "blu tac" which is very useful for things like this... its dry and stcky... it should grab those filings instantly... you can get it at any craft store... check out in the stationary sections of malls...

hope this helps!

Thanks Aniket

Apply some hot glue inside bell let it dry and it should take all metal particle with it.