As with learning anything, you have to start with the basics and hands-on is better than just reading a book. With that in mind, here is Ed’s method for learning vintage sewing machine repair:
1. Start with a Singer straight stitch machine, they plentiful and cheap and parts and documentation are readily available. Scout around for a model 15, 66, 99, or 185 that is complete and has no rust. First scour all your relatives and acquaintance's basements for a freebie. If that doesn't yield results, keep an eye on local thrift shops, local classified ads, craigslist, yard sales, and local auctions and flea markets. If you pay more than $30, you got cheated. The balance wheel should spin but, if not, use that fact to talk down the price. I have paid as little as $5 at a local auction and $2.50 at an antique store that was trashing the heads to make tables out of the treadle cabinets.
2. Go to singerco.com and download the free instruction manual, so you know how to use the machine, then go to parts.singerco.com and download the free service manual – sometimes called adjuster’s manual. For 15 Class machines, I recommend the 15-91 manual in the “Instruction Manuals” section and for 66 Class machines (66, 99, 185), the 66 manual in the “Instruction Manuals” section. I have a re-typed version of the 66 Adjuster's Manual in pdf format with a few added procedures, like disassembly of the tension assembly. If you would prefer that to the Singer download, I am oldsewingmachines at gmail.
3. Clean all the fuzz bunnies out from under the needle plate and remove all the covers and oil the machine. Disregard the oiling diagram in the manual, with oiler in hand, rotate the balance wheel and put a drop of sewing machine oil at every point where metal rubs against metal. Run the machine at full speed until the new oil is worked in and your baby is purring. At this point, you might even want to install a fresh needle and see if the machine will make a stitch. If it does, don't be tempted to stop there - just because it sews doesn't mean it sews as well as it should.
4. Now, get out the service manual (adjuster’s manual) and go cover-to-cover, checking every adjustment in the book – needle bar height, feed dog height, feed dog centering, tension assembly, bobbin winder, hook timing, hook-to-needle clearance, drive belt tension, check spring, and all the gaps that thread must pass through on its way to making a stitch. No special tools are needed, you should have all you need lying around the house.
5. After making any necessary adjustments, you should now have a vintage Singer sewing machine that runs and sews like new and you know why it does. If you have gone through all the above steps and your machine does not sew, perform a search for “vintage sewing machine forum” and join one of the many forums where SM collectors hang out. They are all anxious to show how much they have learned and willingly answer questions within minutes. You will be more credible if you can tell what you have already tried that didn't fix the problem.