To be honest, the standard Lego Technic cylinder engine model is a bit too big for my building scale. Therefore I designed a couple of cylinder models myself. These are compact enough to even fit them into a Lego motorbike scale model!
About this creation
A lot of Lego Technic cars are equipped with V8 engines and motorbikes with V2 or V4 engines. For another project I developed a straight five engine to make it a more compact. It turned out to be actually larger and I was a bit disappointed first. From then I downsized it by rebuilding the cylinder engine from the ground up. I payed attention to the details and utilized every tiny space. On top of that I worked as compact as I could and it worked out pretty well.
Instead of building around the standard Lego Technic cylinder engine, I created a smaller mk1 inline four cylinder engine. The L-shaped gray parts hold the rubber bands and the upper layer of the engine together. The Mark 1 engine rotates well, but it feels sturdy as a result of too stressed rubber bands.
The mk1 straight engine was too straight and too stiff in performance. By shrinking the Mark 1 into the Mark 2 four cylinder engine by a Lego brick size I positioned the cylinders in such a way, that the crankshaft would rotate the full 360 degrees, but not without almost stickiness and tend to block. The engine didn't sound realistic, but rather forced. To make the cylinder engine both move and sound normal, at least one or two cylinders have to be placed in opposite position, which results in a wider v-configuration.
Engine mk2 didn't discourage me to downsize further. In contrary, from this point I saw more unnecessary and too thick parts then on mk1 and mk2. I scrapped lots of parts and mk3 became one of the most supple rotating inline engines that I created so far. I must admit that mk3 also rotates a bit suppler than the mk5.
Inline cylinder engine mk4 has almost the same suppleness of mk3, but I flattened the top by one brick size. The flattening causes a bit more stress in the rubber bands. Although mk4 is more compact than mk3, the crankshaft of mk4 rotates a little less supple, but definitely not less good. The red rubber band too wide, so I used the white one instead.
First I thought the Mark4 inline cyilinder engine was the best I could create, but I realised that it still contains too much parts. I rebuilt and downsized the Mark 4 engine. After comparing Mark 4 to Mark 5, Mark 5 has a super compact appearance and it has the excellent supple rotating qualities of the mk4 engine.
I took some pictures of the original Lego Technic cylinder and compared it to my self-assembled inline engines. As you can see, they share almost the same height, but my most downsized cylinder engine mk5 is three brick lengths more compact.