The instruction manuals of the '20-ies and '30-ies contain a lot of mechanical machinery. Next to the trucks, cranes and large excavators, they have a range of workshop machinery and engines. These models do look their age, they are very 'period'.
A neat example is this oscillating steam engine.
This is from the 1923 (Dutch) printing of the Meccano Instructions booklet for sets 1 to 3. It is built here with early '20-ies parts. For this model the book actually added some explanatory text to the single picture, but to be frank it confused me more than it clarified.
Despite its simplicity, it does nicely catch the essence of the oscillating engine. A short, stocky engine like this would have been used as a stationary engine or more likely fitted as a ship's engine (e.g. driving paddle wheels.)
As usual, the model needed some tweaking and small modifications to get enough clearance for the cylinders and to get it to work smoothly. But then it shows the two cylinders' oscillating motion on the crankshaft very well.
This drawing from the 1922 printing of the Lichtenbelt textbook on the marine steam engine shows the general arrangement of a single cylinder of such an engine.
Very simplified - an enjoyable little 3D puzzle :)