Gather these items:
1) Thick leather gloves
2) Aluminum cookie sheet
3) Hot oven - 350F (Not Celsius!!)

Here's the process:
1) Turn on oven to 350 F
2) Disassemble your engine down to just the crankcase, front and rear bearings, and crankshaft. (Don't lose the little key on the front of the crankshaft!!)
3) Tap on the front of the crankshaft with a block of wood and it will pop out of the back.
4) Put the new rear bearing onto the crankshaft and place this assembly in the freezer
5) Put the crankcase on the cookie sheet, rear of the engine pointing down, then place the cookie sheet in the oven.
6) Listen carefully to the oven, and in about 10-15 minutes you should hear the rear bearing fall out of the engine and hit the cookie sheet.
7) Put on your leather gloves, and grab the freezing cold crankshaft and rear bearing from the freezer.
8) Pick up the engine from the oven, turn it over, and slide the crankshaft w/bearing right into the crankcase.
9) Let the whole thing cool, then re-assemble.

I Hope this helps!!!