I found a Classica 90 that wouldnt reverse. When I took it apart I realized the stitch width mechanism was stuck.
The reversing mechanism manipulated that part to reverse. Problem- mechanism and shaft super stuck. I took it out and forced the shaft to turn and lubed it with a general thin oil. I didn’t know the mechanism; or anything about sewing machines. The give-away was a spring connected to the mechanism. Since it was stuck the spring didn’t seem to have any function..... until I realized it had to be moving. Hope it makes sense.
One screw top back to removed cover. It glides up.
1 screen behind reverse button removes front cover. Also slides up. You reach from behind to get the mechanism out( 2 screws holding small shaft. 2 springs off also. )
Front cover needs to come off to dissemble stitch width turning nob. Has to come of to release the reversing/stitch width mechanism.
It’s not as difficult as it look. You might need a small plier to put springs back in place
Foto shows the stitch width mechanism. The front spring is attached to the part that was stuck.