It'll be stuck on the old gasket. Make sure you HAVE got all the screws out - ALL of them. Then hit it with a large rubber mallet or a big bit of wood. Hit each side in turn until you break the seal. Don't lever it with a screwdriver or a chisel as you'll distort the face of the crankcase and have a permanent oil leak when you've got it back together.
If the sump is rusty you may need a new one by the time you've got it off.
Chicks Fan, December 2008
