When I was a kid my brother owned a toy steam engine. It was similar to the Wilesco engine pictured to the right. You could connect a belt to its wheel and drive toy pieces of machinery with it. I remember it having a miniature table saw that could cut paper. We chopped up a lot of paper with that thing.
As you can imagine, it vastly entertained a young male's mind. There was an element of danger about it, with its little boiler of scalding water under pressure chugging away and, in our fevered imaginations, always ready to explode at any moment. Thus, we had great respect for the engine's pressure release valve. We fiddled with it endlessly to make sure it wasn't clogged.
However, the point of this post isn't really nostalgia. The other day I ran across a website called Animated Engines. The owner of it has methodically drawn frame by frame diagrams of engines with Autocad, which he then animates (and the speed of his animated gifs can be controlled). He's got 7 types of internal combustion engines, 10 steam engines, and 4 Stirling engines diagrammed. Quite fascinating to see all the approaches to building engines.
It was watching the animations of the steam engines that reminded me of my brother's toy. As much as we played with it, and as much as we fretted over the pressure release valve, watching the animation made me realize I never actually knew how it worked. Turns out the things had some really clever valve mechanisms to spin the drive wheel. The variety of their form is also interesting.
The site is worth spending a bit of time exploring.