Kenmore Sewing Machine 385.1695180 internal repair?

My machine will not follow the cam pattern and switch from straight to zig zag, it only does straight stitch. I evaluated all the moving parts internally and discovered that there is a rod that connects to the width selection and it is connected with a screw that screws up from the bottom to hold the rod tight. If I add pressure manually to this rod, and use the wheel manually, the needle appears to follow the cam pattern and operate. Obviously you can't sew with the top open and manually operate that rod. Do you know how I can get that screw tightened without disassembling a lot of parts. Do you know where I could get a schematic of the interior or a proper angled screwdriver to tighten and perhaps fix this machine? Any suggestions? Thanks