Not to take anything from Maryak and his engine (a fine project, and an excellent writeup), but I thought I'd toss out another nominee.
Not an engine, but the boiler project firebird made, and his step by step documentation. He tried some neat things (pressing the end caps) that I would otherwise have not considered. I really like that he shows both what worked and what didn't. It also shows his experimentation with burners.
I think, reading the whole thread again, that one could make a boiler using the techniques shown and have a reasonable chance of success.
Not an engine, but the boiler project firebird made, and his step by step documentation. He tried some neat things (pressing the end caps) that I would otherwise have not considered. I really like that he shows both what worked and what didn't. It also shows his experimentation with burners.
I think, reading the whole thread again, that one could make a boiler using the techniques shown and have a reasonable chance of success.