RE: Installing the Pinion Gear on a brushless motor.
Here are a couple of suggestions that I've done in the past.
1) Find a small drill bit about the same size as 2mm which is the shaft size of your motor and drill out the pinion. Once you've done that make sure the pinion can side onto the motor shaft. Next put the motor into the gearbox this way you can line up the pinion so it messes with the spur gear. Put some red locktite on the motor shaft and side the pinion in place. Wait about 5 to 10 minutes and your set. If you ever what to change the pinion a pinion puller will take the pinion off with no problems.
2) Most of the manufactures use an arbor press to put pinions on. The secret is that both sides of the shaft must be anchored so the shaft doesn't get pushed out of the can.
3) Buy a Himax aluminum gearbox for around 30 dollars and the pinion gear is kept on with a set screw.
4) The last thing that I've been using that seems to work will is go to the hardware store and buy a C clamp. Drill a hole in the base of the clamp so the shaft of the motor can exit allowing the pinion to be pressed on.
Bevo