Resurecting a Syma F4 with busted main motor brush

Since the syma F4's mainmotor sparepart are quite rare, i replaced one with V911, they are exactly identical for the size, it's an easy one to one replacement, on the other hand the pinion is not compatible, i uses the original nylon pinion came with the F4, and removed fragile V911 brass pinion from the spare v911 motor.. It's works, but i might have to replace the 2 y.o. battery, that only stands for less than 2 minutes ;)