Picture of Motor Boss

The issue of whether a specific old Singer (or other machine) can or cannot be converted to hand crank seems to recur about every other week. For the record, the only reproduction hand crank available is the one for Singers. If you have any old sewing machine that is not a Singer and want to convert it to hand crank, you will have to find a matching original hand crank mechanism, or have something machined. As to Singers, only those Singers that were equipped for motors or hand cranks in casting design, i.e. those that have a cast in motor boss, will accept the reproduction hand cranks. Here is a picture of the Singer motor boss:

Here you see a "motor boss", i.e. the raised part of the casting that accepts the motor, or hand crank. It has ridge in the middle that matches an indentation in the hand crank or motor base, and a threaded hole in the middle whereby the screw holds the motor mount or hand crank in position. These bosses are standardized on the older Singers. When used to mount a hand crank, they center the crank's motion on the middle of the hand wheel and assure that the engagement finger is the right height. Some later Singer models use the same system, but the geometry is not quite identical and the hand crank may not work without the drilling and tapping of a new hole just above or below the existing one. (I can't quite remember whether it is above or below)