LEGO vacuum engine with quick-reverse mechanism

I was bored yesterday, so I did what any other normal person would do: shut myself up in the workshop for hours and build a vacuum engine out of LEGO. I built an engine with two cylinders in such a way that it never has to be pushed to get it to start.

It turns out I don’t have a vacuum that is strong enough to power this thing, but a little creativity (and an electric motor) allows me to demonstrate that it should work perfectly fine if I had a larger vacuum.

One thing that I added to this that I haven’t seen on many other LEGO vacuum engines (or even pneumatic engines, for that matter) is a simple and fast way to reverse the direction that the engine runs without having to even partially disassemble the engine.

Okay, okay, maybe pulling one of the gears out of mesh to reorient it kind of counts as disassembly, but it’s a fair compromise. The reverse-while-the-engine-is-running mechanism requires a differential, and all the LEGO differentials that I have have too much backlash for the engine to be able to run with the best timing. But rest assured that it is possible!