The Stirling engine is a type of external combustion engine invented by Scottish engineer Robert Stirling in 1816. It works because of the temperature difference between its hot and cold end. The major difference maker in its design over other heat engine is the fact that it can use almost any kind of heat energy. From a wide variety of fossil fuels to many types of reusable energy sources like solar power. Great flexibility is also visible in the fact that some smaller models can run on temperature differences as low as half a Kelvin. Stirling engine was the first hot air piston engine used since 1818. when it was utilized for pumping water into a quarry. Over time with the invention of Otto and diesel engines, Stirling's engine being inferior in power, slowly becomes forgotten. In the future, given the fact that fossil fuel reserves are running low, it is expected to see a new rise in usage once advanced but now unrightfully neglected machine. There is no lack of variety in the designs of this engine. Considering mechanical configuration, it is usually divided into three major groups. Alpha, beta, and a type closely described in this paper, gamma. Other than the three most common ones, many other interesting configurations exist such as rotary Stirling engine, free–piston engine, or flat engine. The final work named Modification of a Stirling engine is made in two parts. Theoretical, where it was shortly explained its history, the key principle of its work, biggest advantages, and disadvantages, and the second practical part consisted of a calculation of the flywheel, its production, and an attempt to fix the non-working model of the engine.