spur gear melted

ive gone through 4 spur gears now...it always melted and i dont have a clue why? brushless e revo

where and how is it melting?
gear mesh could be to tight. the revo have a slipper clutch (i don't remember) if it's to loose it could be slipping to much, causing friction and heating it up. you could have excess drag in the drive line somewhere that is somehow manifesting itself in the spur for some reason

you might have a to big or to small pinion gear that is causing the motor to heat up more

check the tooth sizes on both the pinion and spur gears.

I've gone through 3 just because of stripping, the pinion slides forward on mine, yeah try loosening your gear mesh or change geat setup.