rotor snaped on speedpassion v3 motor

[moggy12]

my speedpassion v3 13.5 brushless motor was making a right noise so i took it apart to find that the long pin where you connect pinion had come away from the main rotor i think the motor is great never let me down before so i have ordered another v3 13.5 motor what can i do to stop this happening again the car it goes on is a xray t3 thanks for any replies