I love those old Singer 15s and the clones - very often I've had to take the tension apart and put it back together - a good cleaning is helpful. The manual here will help. I enlarged the pictures so I can see it at a glance.
http://www.tfsr.org/pub/technical_in...echanism_2.pdf I figure if I can follow a pattern I can rebuild a tension. Take your time and don't lose your screws...