Vintage new home (XR-VII model 990)sewing machine...

Question

Hi there, my vintage machine has a handwheel that is soooo hard to move. I can move it though and the rest of the machine seems to move properly although very slowly. there is a gear connected to the wheel that can move freely when I move the belt clockwise but when I try to move it/them counterclockwise it very difficult. I have tried to oil, clean etc. and have removed the outer casing to the machine. any ideas? when I plug in the machine the motor seems to want to run but the wheel is so hard to move that it can't.