RE: How tight should my brushless motor aginst the sprocket?
Icedude,
you're doing O.K., but the easiest way is to put a piece of paper (32 and 48 pitch gears will work with this - 64 pitch is adjusted a little differently), like receipt paper, between the pinion and spur gears, then tighten the motor screws down. Remove the paper, and they are properly adjusted.
Aplekan,
don't run the car too long with tight gears. You'll ruin the electronics if they get too hot. Adjust it using the above method, and you'll be O.K. Check the tightness of all the screws on the car periodically, so this doesn't happen again.