This is the reason why Texmaco, despite originally a textile manufacturer, could make its own engine.
The parts presented in the videos above are simple. But designing a working, feasible engine, as cheap as possible and with good power output is another thing.
Ever heard about Indonesians making an engine (any type of engine) with >40 hp power? I certainly never, such feat need a teamwork of experienced engineers. Texmaco can produce engines, but they're license-produced them, the same happened with Boma Bisma Indra with their Doosan engine.
The engines that we design ourselves, like Rusnas engine and Fin Power engine, only has small output. Need more effort, cost, willpower, and much more manpower (engineers who design their parts) to make more powerful engine.
Like @Nilgiri said ..It needs concentrated funding (to make the organisation of people) and then sustained import of lot of several heavy capital machinery.
Preferably as early as possible.
A deep study as possible of how Japan and then Korea did it...(and then became involved heavily in India's efforts later in cold war) for example is useful.
The later you get into this, the more expensive it becomes as labour+corporates are pulled+competing in all kind of other sectors downstream.
Regather + redeploy energy (and much more competitive world for capital intensive machinery + investment etc for it) is basically lot higher now in every opportunity cost and price level.
This is big problem confronting India and electronics production for example right now.
It takes a concentrated effort and sacrifices to make such endeavour comes into reality . An efforts we lacked and sacrifices we couldn't dare to stomach ... Yet , we could spare an effort try to create an overrated turboprop aircraft that never sale ...... Ironic isn't ??
One thing for sure is ....
Without a natural domestic market to absorb the output every government oriented project are bound to fail...