My first post on the forum. Mt Pfaff 545 slipped gears and went out of time. I've readjusted the gears so I've got the hook grabbing the needle thread ok, but when it rotates around with the thread, a small arm ( B/C Opener ?) touches the bobbin and will not allow the thread to pass through and creates a tangled mess . Sorry I don't know all the part names. Any manual I've looked at doesn't show that nor does any on line video. Its something I never paid attention to when it was running fine so I'm not sure exactly how its supposed to operate.