I recently revived a Singer portable with basic zigzag. I did a search on youtube.com for reviving my machine. Several sites came up and I chose one that was over 50 minutes long but it was thorough. I took off all the shell piece by piece and cleaned with Qtips and oiled everything that moved. The last step was to take off the bobbin case and exposed a little black cover. Upon taking it off there were the gears for the bobbin encased in a thick grease mostly black. I cleaned that out with Qtips per instructions. Then he said to fill it up clear up with vaseline. I did this and worked it some. It turned so easy and when I pushed down on the foot pedal it purred like a kitten. It seemed that that the bobbin gear thing was what was so bound up. Hope this helps.