How do I get the crankcase cover off a Craftsman 4.5hp lawnmower engine?

I've drained the oil and removed the bolts (of course) and the cover came off the gasket, but wont move more than about 1.5 inches off the blade shaft. I pull really hard but it just stops suddenly like it wasn't meant to be removed. I can't see anything that would hold it on there. Help?