Originally Posted by mikeread

I had this problem once years ago, nothing would shift the pedal spindle and the hex had rounded out.

I got a mate to weld a large nut onto the pedal spindle (pedal was scrap anyway) and with a large spanner and pipe and the crank in a sturdy padded vice we loosened it off. Once the seal was broken it screwed out easy by hand.

Make sure you are turning it the correct way, it can be confusing when you are working from the back and you have to account for LH or RH threads on each side.