It's a outrunner motor thats why you can lift the outer case, If the pinion gear wasn't on it you can pull it apart and look at it! Scared ya didn't it?
Zim what did I tell you about putting stuff together upside down hahaha. Long as it works is what really counts. What works for me may not work for you and vice versa. Interesting enough my original main shaft collar was the same on the top and the bottom (rounded), lasted about 10 flights before the set screw came loose and distroyed the threads in it.
I just want to get my belt to make friends with my rear sprocket and follow it around...