Welcome. I'm not familiar with your machine, in particular. I don't know if this would be what you need or not.
https://www.youtube.com/watch?v=sNULAP4YoOc
The manual at
http://www.needlebar.org/main/manual...evs/index.html isn't very good for instructions on threading the bobbin. There is a good article about a Singer long shuttles can be found down the page at
https://w.treadleon.net/sewingmachin...vsshuttle.html It is possible the spring has rusted and/or has been screwed on too tight to allow thread to pass through it.
Good luck on getting it working properly.
Janey - Neat people never make the exciting discoveries I do.
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