About a week ago, I fixed a lady's sewing machine. When I didn't charge her, I told her all I did was replace her bobbin case with one from a parts machine someone had given me. I told her if she hears of anyone about to toss out a machine, please grab it for me because I can always use parts. She said she had a machine out in the garage that was worn out and good only for parts, I could have it if I wanted it.
Turned out to be a Singer 401. I am partial to the Singer slant needle machines because a 301 was my first sewing machine and a 401 was my second, so I took it.
She said that it had been used so much that thread has worn a groove in the housing of the machine, the thread kept getting caught in the groove and shredding or breaking. I looked closer and, sure enough, there was a groove just above the last thread guide on the housing. I threaded the machine and she was correct - the thread runs right through that groove.
I toyed with several options: grinding the groove smooth, installing a rub strip over the groove so the thread would no longer catch in it but being low-tech, I opted to just bend that thread guide at the groove about 1/8" so the thread no longer runs through the groove.
In a quick test, it sews fine. I need to clean and oil and give it a real test tomorrow.