Holy cow...do you mean to tell me that you are wanting to build a motorized bike, and you can't re-assemble the rear axle, and bearings?
Wow...good luck with actually being able to put the motor on the bike. And good luck getting the rear sprocket mounted to the wheel.
If you can't figure out the rear wheel bearings and axle, how in the world do you expect to build a safe bike with a motor on it? Seriously, if you can't figure out how to re-assemble the rear axle, getting the sprocket onto the hub will be a real challenge for you because it's not as easy as just putting some nuts and bolts through some holes. Look out for that pesky coaster brake arm!
Geeze, I can't understand how there are so many people in this world who do not have BASIC bicycle mechanical skill and knowledge. All I know is that when I was 10 years old, I completely dissassemble my bike, clean and grease all of the bearings, and re-assemble it correctly.
I don't mean to sound like a jerk or anything, but seriously, there are a ton of things that you need to be able to do in order to put a motor on a bike to make it safe, dependable AND getting it running right.