Five-stroke engine In 1879, Nikolaus Otto manufactured and sold a double expansion engine (the double and triple expansion principles had ample usage in steam engines), with two small cylinders at both sides of a low-pressure larger cylinder, where a second expansion of exhaust stroke gas took place; the owner returned it, alleging poor performance.
In 1906, the concept was incorporated in a car built by EHV (Eisenhuth Horseless Vehicle Company) CT, USA;22 and in the 21st century Ilmor designed and successfully tested a 5-stroke double expansion internal combustion engine, with high power output and low SFC (Specific Fuel Consumption).23 Six-stroke engine The six-stroke engine was invented in 1883.Four kinds of six-stroke use a regular piston in a regular cylinder (Griffin six-stroke, Bajulaz six-stroke, Velozeta six-stroke and Crower six-stroke), firing every three crankshaft revolutions. The systems capture the wasted heat of the four-stroke Otto cycle with an injection of air or water. The Beare Head and "piston charger" engines operate as opposed-piston engines, two pistons in a single cylinder, firing every two revolutions rather more like a regular four-stroke.Źródło: https://en.wikipedia.org/wiki/Internal_combustion_engine
On the basis of the fact that - from the need to maintain a balance, and ending with the fact that driving license for motorcyclists is difficult, because the instructor is not in the same vehicle, every student - we can say that getting a license for a motorcycle requires really a lot of effort.
However, this does not discourage people who want to manage their own engine.