Don't be sorry... There could be several reasons why your engine doesn't run.
The dimensions of your engine seem not to be the cause of the problem. Such an engine should work.
1. The copper pipe cap thickness can be whatever you find i your mess box. If it is very thick it will need time to reach 100°C (212F).
2. The boiler is not necessarily to be filled but it must contain enough liquid water (due to its size). As you observed bubbles there is a possibility that there was not enough water. Thus, when the air trapped in the engine was heated it expanded up to the end of the pipe
and without water the engine couldn't run.
3. If the brass diaphragm was too thick, it would prevent the engine to make noise, but not to deliver pulses.
4. The boiler is possibly too big to be heated effectively by a "tea light" candle. Add a second wick (or two) to increase the heating power.
5. The cause of the problem could also be a leak. An engine could be tight at ambient temperature and leaking steam when hot. But in that case, generally the engine starts and runs for some seconds before burnout.
Good luck! And when you have found the cause, please let us know.
--- In email@example.com, William Abernathy <william@...> wrote:
> While reviewing Jean-Yves's diaphragm boiler plan, I was struck by one
> post-build photo that showed three birthday candle stubs under his
> boiler. Emulating this, I got the desired rattle out of my little
> engine. So, mission accomplished, I now have to figure out how to
> produce enough heat (safely!) to make this go.
> Sorry to squeak for help before trying out everything first. I'll send
> photos when I can!
> William Abernathy
> Berkeley, CA