This is a cut-and paste from a very old old Singer sewing machine forum post on Yahoo Groups, whose author’s name has been lost to the mists of time. This applies only to all-metal machines from the 1960s or earlier!
Cleaning methods (with comments on minimizing splash on a Singer Slant’s internal motor. All others simply remove the motor):
1) (My favorite, many disagree).
Get the following:
An aluminum turkey pan
A large tough plastic leaf bag
A few cheap china paint brushes
Some really cheap clay kitty litter
A gallon of kerosene (not lamp oil, but real kerosene. I have a 1 gal. gas can marked “Kerosene” all over with a sharpie and buy it at a filling station).
Oil and grease for the machine. Many of us use Tri-Flow, a bicycle oil, as it has Teflon as an extra lubricant and if the oil evaporates some, the Teflon remains. But Singer oil and grease from Wally-Mart will be just fine.
Put the pan in the bag, and the bag on a back porch, breeze way, or garage with no flame sources.
Remove covers and put the machine in the pan and drench everything but the motor in kerosene. If you splash some there, no big deal. Tie the bag off.
The next day, use the china brush to splash the kerosene around all of the moving parts again, and scrub at tough looking spots.
Do it as many times as necessary to cut through the gunk.
Take the machine out, set it on some paper grocery bags or newspaper
to drip dry.
Pour the kitty litter in the dirty kerosene and now you can tie off the bag and pitch the whole thing with a clean conscious.
Oil and lube the machine.
2) Do something similar to the above but use PB Blaster (my favorite, can be found at Auto-Zone, Pep Boys, etc) to drench the machine and use the china brush to scrub what you can reach. Some like, some hate WD-40. Don’t use a silicone spray as it won’t cut the gunk as a petroleum (or fish oil type WD-40) product will.
Auto solvent is safer then kerosene, but about three times as expensive. I have also used Simple Green, but don’t like flushing an iron/steel machine with water so used kerosene anyway as a flush.
Last updated January 31, 2007
Sewing Dude 
My sister rescued a Singer 66 from a dumpster.
I am not sure my method is correct; but I have never seen a froze-up rusty old singer before, that was not well cared for. So, I felt like I had nothing to lose by using what ever would loosen up the crusty old machine.
It took 3 days of sitting outside in the heat (sunshine), after oiling & spraying all the mechanisms with PB Blaster, I finally got that froze up machine to move. I had to place a stick of wood against the lower mechanism & whack it with a hammer; whacking the mechanism back & forth, all the while adding more oil & PB Blaster to every metal part, to get it to move.
Now it is freed up; I am wondering if I need to flush the PB Blaster out of the machine.
What is the kitty litter for???