So my repair job was to simply replace a rewind spring on my lawn mower.
Okay I'll back up. In pioneer days , to start a small engine, you would wind a rope around a pulley and pull. If the engine started great! If the engine didn't start you wound the rope around the pulley and pulled again. Sometimes you had to pull 10 times for the engine to start.
So some wise guy thought, "Why don't we have something to rewind the cord automatically and make things easier?" Well the gizmo was invented and was part of small engines.
Now I know some people's eyes are starting to glaze over and look for the end of this post. My eyes are glazing over too.
Okay back to my repair. The "unit" consists of a housing to hold the spring, a pulley with a rope, a worm gear and small plastic gear. The housing and pulley are on a shaft. The housing doesn't turn but the pulley does turn.
Much of this you can't see because it's enclosed. Much of it you can't see because it's underneath whatever. Your hands have to feel things to put them back together.
The spring is a challenge to wind. First discover which way to wind it. It is wound opposite to the pulley with the rope. The rope is to turn the pulley counter clockwise. Too complicated for me. It took me four tries to get this right, but I did get it. I'm not going to tell about my dumb mistakes.
I'm not going to give details because who cares? Today most lawn mowers start by turning a switch!