Watch out for using "glazed cotton threads" or thread designed to make hand sewing easy. but the coating will mess with tension disks and bobbin springs gumming them up. With old style long bobbin VS shuttle machines I think it is over oiling the needle bar which will /can cause oil to find its way under the tension spring. Often these old machines will sew with lint trapped and only when you change your bobbin thread to a different weight will you have trouble with bobbin tension. Cheapskate - Yorkshire man here who often sews with thin overlocking thread in both bobbins ;-) in machines that are over 100y old. I trap a think bit of wood when I lower the presser foot and feel the drag of the top thread as it passes out through the eye of the needle and under the gap I left under the foot; then test the lower bobbin tension by pulling on it. Often I am looking to see if the tension is constant. It is surprising how low the bottom bobbin tension needs to be.
Bent out of shape... A previous owner had managed to bend the tension spring on my 1950s machine. I did manage to make a small wood V block and used a piece of hard wood shaped like a large flat head screwdriver to "sort of" burnish / rub the inner curve of the spring to bring it back to a tighter curve. I did have another spring out of similar machine to compare the curve. This is not a job for a beginner so you should try it out with some scrap spring steel first. I do have a an engineering background back in 1983 I straightened a pair of motorbike telescopic front forks (they were bent like a banana ) however I had access to V blocks and a large hydraulic press.
Watch out for using "glazed cotton threads" or thread designed to make hand sewing easy. but the coating will mess with tension disks and bobbin springs gumming them up.
With old style long bobbin VS shuttle machines I think it is over oiling the needle bar which will /can cause oil to find its way under the tension spring.
Often these old machines will sew with lint trapped and only when you change your bobbin thread to a different weight will you have trouble with bobbin tension.
Cheapskate - Yorkshire man here who often sews with thin overlocking thread in both bobbins ;-) in machines that are over 100y old.
I trap a think bit of wood when I lower the presser foot and feel the drag of the top thread as it passes out through the eye of the needle and under the gap I left under the foot; then test the lower bobbin tension by pulling on it. Often I am looking to see if the tension is constant. It is surprising how low the bottom bobbin tension needs to be.
Easy if you know how! Thank you.
Bent out of shape... A previous owner had managed to bend the tension spring on my 1950s machine. I did manage to make a small wood V block and used a piece of hard wood shaped like a large flat head screwdriver to "sort of" burnish / rub the inner curve of the spring to bring it back to a tighter curve. I did have another spring out of similar machine to compare the curve.
This is not a job for a beginner so you should try it out with some scrap spring steel first.
I do have a an engineering background back in 1983 I straightened a pair of motorbike telescopic front forks (they were bent like a banana ) however I had access to V blocks and a large hydraulic press.