"Some" Singer motors have a felt pad surrounding the bronze (or whatever it's made from) bushing at the ends of the armature shaft. You can see this through the air vents. Oiling that and then letting the motor sit so the oil soaks in will usually improve the motor's performance and quiet it down. I've done that to several of them.
I've also used break cleaner and denatured alcohol to clean the commutator, brushes, and brush tubes. So far I've not set any of them on fire by doing so.
The cure for setting things on fire with electrical contact cleaner or other flammable chemicals is to let it evaporate and dry before powering up the motor or electrical system. That's only common sense and is probably mentioned in the warnings on the can.
Joe