Small Engines (Lawn Mowers, etc.): changing engine on two man augers

Question
I have a general brand two man augers I'm trying to remove the engine from the gear drive to replace the engine. All the bolts are out and the gear box moves 1/2" but the shift must have a key or keeper ring...I need to get them apart ... how? It still rotates but I can't get them apart...

Answer
There could be a key, a burr on the shaft or the clutch could be preventing the engine and gear box from coming apart.  

If you have a 1/2 inch of room you should be able to get a pen light inside to illuminate the area and then do a visual inspection to see what is binding.  

Can you attach a picture of the engine?
Eric