well easiest way would be to first learn how the coding of the engine works, then after that you just need to model the engine and create a basic jbeam structure for it
I recommend using automation. I like to create engines in automation then use one of the engines in-game as a base and tweak the code to my liking.
for the code yeah but automation engines model are incredibly high poly and also have modeled internals making them unstable and laggy in game compared to standard models