During another project I created my own version of a Lego Technic cylinder engine. My goal is to replace the regular Lego Technic cylinder engine for my own future models, because I think that it has become too big for the models that I want to build. For achieving that goal I have rebuilt the cylinder engine as compact as I can. Now it even fits in 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. To create a more compact inline cylinder engine, I developed a mk1 straight five engine. Somehow it turned out to be actually larger and from that point I kept downsizing my model. I payed attention to the details and to work as compact as I could. I think it worked out pretty well.
Instead of developing the five cylinder engine further, I created a smaller mk2 inline four engine. I removed the spring feathers from mk1 to save space and replaced them by Lego rubber bands. Due to a lot of stress on the rubber band it felt too sturdy when in motion. The L-shaped gray parts hold the rubber bands and the upper layer of the engine together.
The mk3 straight engine is too straight and too stiff in performance. I reduced the width by shrinking it by a Lego brick size. By doing that I made myself position the cylinders in such a way, that the crankshaft had to move all the cylinders in one round. That resulted in an way too heavy, almost sticky, tend to declining rotation and above that the engine didn't sound realistic. To make the cylinder engine both move and sound with a some ruff in it, at least one or two cylinders have to be placed in opposite position to the remaining others. That's what I learned from inline engine mk3.
Engine mk3 didn't discourage me to downsize further. From this point I saw more excess and too thick parts then I saw on mk1 and mk2. I scrapped lots of parts and mk4 became one of the most supple rotating inline engines that I created so far. I must admit that mk4 also rotated a bit more supple than the mk6.
Inline cylinder engine mk5 has almost the same capabilities of mk4, but I flattened it out on the height by one brick size. The flattening causes a bit more tensity in the rubber bands. Although mk5 is more compact than mk4, the crankshaft of mk5 rotates a little less supple. The red rubber band was too big in diameter, so it couldn't hold together the top of the engine. Instead of that I used the white one.
First, I thought mk5 was the best I could create, but then I realised that it still has too much parts. I rebuilt, then downsized it. Compared to mk5, mk6 has a super downsized appearance and it has the excellent 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 mk6 is three brick lengths more compact.