The $29.99 all-metal desktop Stirling engine kit is one of the simplest ... sells for $89.99 and is functional when assembled. The model is advertised as being suitable for ages 12 and up.

It shouldn’t come as much of a surprise, then, that you can also still buy and build the Visible V8 model engine kit, first sold by Renwal in 1958 and one of the longest-selling plastic model ...