.........there must be somthing wrong somewere to need a heat sink and a fan on the motor,there is no way unless you cut a big hole in the shell that the shell will fit over the fan
and i dont think it will last 5 mins in a race without some one hitting it,if you go out door it will be a nightmare coz the chassis will get so much crap in it because of the bit missing
as will the fan,i know iv not been much help,does the car run free across the ground if you push it slightly if you disconect the pinion,if yes is it meshed to tight,