Hello everyone. I recently bought '81 bayliner with volvo penta 280 outdrive. It will not shift into foward gear. It does shift in neutral and reverse. I found a schematic for it:

I can shift it foward by twisting Eccentric piston #46 with plyers when the #49 screw is loose. As soon as this screw is tightened the piston will not go into foward position. What could be wrong? and is there a quick fix for this?

Also i should notice that when i am in neutral and i rev up my engine the transmission switches into rear by itself. I guess from the vibrations.