I built a sterling engine some years back. It worked really well, except I mage the flywheel by hand. I just bent some round rod into a circle and added some round rod spokes. It was not balanced even a little and would dang near fly off the table if I put any more heat then just a small candle to it. But it was fun to do.
I have seen some videos of some really nice ones, if you have a mill, lathe and all that stuff.
I love that tinkering in the shop time.