Simple steam boat (part 3, the proper pop-pop engine)

So, this is the pop-pop (diaphragm) motor. I used the concave bottom of an aluminum can and part of the can wall, 1/8" aluminum tube, m3 nuts and lots of high temperature silicone. I made the threads on the aluminum tubes using an m3 nut, but ideally I would use a threading die. I honestly don't like this type, its neat because of the noise but it's hard to make, unstable and doesn't withstand high temperatures (I used a candle because the flame of an alcohol lamp is too hot).