This is one of a couple of steam toys that I have sectioned for demonstration purposes. This one is (was) a Mamod SE3. (see here for a whole model)
All significant parts have been cut open to enable viewers to see what's inside. This includes the boiler and it's fittings (safety valve, whistle, throttle, overflow plug & chimney), firebox, burner, one of the cylinders and one of the port blocks.
The sectioning was done mainly with a junior hacksaw, finishing the cut surfaces with a needle file and emery cloth. One or two tricky bits were cut with a carborundum abrasive blade in the hacksaw. The thin sheet of the boiler and burner were cut with special shears. Most of the moving parts are still movable. The exception is the throttle, which I had to glue in place in the open position. The moving parts of the whistle and safety valve still move, although the bodies are glued into the threaded bushes. The cylinders and pistons are, of course, fully functional (except that they are no longer steam tight!).
The boiler had previously been repaired, leaving a bit of a mess on the inside. This didn't matter before sectioning but is clearly visible now. I tried to tidy it up a bit but it's still obvious what has been done in the past. In a way, this adds to the interest!
I have replaced the pulley on the crankshaft with a Meccano sprocket so that it can be motorised.
I have also sectioned the engine unit from a Wilesco D16. This is a double acting cylinder with a slide valve. (This can be seen here.)