Thank you for your question.
I can understand your concern when the bobbin case will not stay into the shuttle race.
There can be a couple of reasons why it keeps popping out.
I believe however that this machine is from the late 60’s or early 70’s.
• One is if the thread is being caught in the race hook and center pin if the hook is out of time. It will rap around the center pin and when the pick lever on top of the machine goes to tighten the stitch it pulls the bobbin case and shuttle race out of position.
• I would suggest that you have the sewing machine shuttle hook timing checked by a sewing machine technician.
• The other problem can be if the shuttle race ears are not locked into position to hold the shuttle cover in place.
• I have included a picture of the shuttle race and the top and bottom thread path as the machine goes through its making of a stitch.
• The Top thread is the solid line and the dotted line is the bottom thread and they both have to make this path around the shuttle to form a stitch.
• The first picture shows the hook in its farthest left position.
• The next picture shows the hook starting to move to the right and the needle is down to deliver the top thread so as the hook point travels to the right it will pick up the upper thread and raps it around the lower thread and slides through the shuttle spring and out the other side to form the stitch.
• If it is even slightly out of time it will not release the thread and it will get caught in the shuttle and as the take up lever pulls the thread it dislodges the hook and race parts.
I hope this will help with understanding how this works and that is requires a special timing tools to get it adjusted correctly.
Thank you for using Manage My Life.