How do we make our machines look and sew like a new machine?
After an initial scan for missing parts and obvious problems, we start by just turning the hand wheel to feel the action.
Often the machine will feel stiff and sticky, due to dried and hardened oil and grease in the joints and gears. If it turns without undue resistance, the machine is plugged in (if it's electrified) and run, to further assess it's present condition.
The fun part is next. The machine is opened up at every access, and thoroughly brushed out and vaccumed to remove all the accumulated dust and lint. Without this neccessary step, the new oil can draw abraisive particles down into the joints and moving parts, and cause additional wear. Wads of oil-soaked lint will jam a machine, change tolerances, and cause more trouble.
The hand wheel, bobbin case, hook, and tension assembly are disassembled and removed, and rotating parts checked for thread jams. It doesn't take much to add drag to the machine's works. On some machines, a little thread around the hook or hand wheel is enough to stop the rotation, entirely.
Now is a good time to check for wear and damage. Wiring can have cracked or frayed insulation, belts can fray and separate, the hook can be worn, bent or damaged.
Usually the needle bar and linkages and the presser foot bar and it's related assemblies are removed and they go into the alcohol bath and the needle gets replaced because it's the leading cause of problems with sewing machines.
We disassemble as much of the stitch forming section as seems appropriate in each case and polish the parts when they come out of the alcohol bath. Sometimes the contol knobs and shafts are coated with dried on oil and need to come out for cleaning and generally, anything else that needs attention gets our care.
The motor gets opened up and the commutator polished and shafts cleaned and oiled. Motor brushes can wear down or soak up oil, causing the motor to smoke so they come out and get cleaned.
Gear assemblies are cleaned of hardened and dirty grease.
It's important to use the right oil. Never use household oil or WD-40 to lubricat a sewing machine. The correct oil is sewing machine oil. It won't dry out and turn into varnish like household oil. And go lightly. Just a drop or two at each point of movement. More isn't better.
After the machine is reassembled and adjusted, and then tested, the exterior gets a thorough cleaning and detailing to return it to it's best possible condititon.