Hi guys. I also had to replace my main gear in Belt CP v2. I got the Blade 400 main gear without the bearing so had to use the bearing from stock gear.
I think this is very important for anyone swapping bearing on Belt CP.
Important, this bearing is like a cone. So you have to pay attention from what side its coming out and how its going back in.
First, to remove the bearing, you must hammer it on the side that does not have the arrow and some writings.
Second, it goes back in same way it came out, do not flip it around. The side you will hammer on this time will have the writings and the arrow on it.
Also make sure you use a little bit of grease or oil on the inside of the gear where the bearing will go in and around the bearing. Also make sure you position the bearing as straight as possible before hammering.
Another thing specifically in regards to Blade400 main gears is that the part that holds the bearing is actually thicker than Esky gears. So I had to sink in the bearing about 1 mm in on the side with the arrow and the writing to have the bearing lip comeout a little bit on the other side. This is so the gear has some clearance between the frame. This is my opinions from own observation and use of digital caliper.
Hope this helps.