This is the tension mechanism on most of the machines labelled simply "BU" or "BF" on the pillar, and some labelled "Nova," all with the "VN" logo on the bed.
To remove it, loosen the set screw on the side; you need to raise the presser-foot to see it.
Slide the entire mechanism out:
Take it apart and clean everything; be careful not to lose the pin that lives inside the post.
You can see the pin between the threaded prongs in this picture:
After inserting the pin, put the other pieces back together in the same order they came apart, screw on the cap, slide back into the machine and tighten set screw.
