Good proportions for a metronome engine.

[Jagang]

Hello, newbie here.

I've been trying to build a simple engine for a while, but everytime I fail, even at making simple tin can engines.
Somwehere along the line, there's always something going fatally wrong. Hindight mistakes.
Materials that don't behave like expected.
Working piston balloons that I don't get tensed up properly (tense on the outside, sloppy on the inside.), because the rubber appears to be unequally distributed over a balloon.

So I found the metronome engine online, and I thought: "This is so simple, if I cant make this one, I might as wel just give up."
Just a displacer/working piston, with a pipe on it, either filled with air, and maybe some water in a lock.
How hard can it be, right?

Well, I kinda built one, but it doesn't kick at all.
Again, I experience problems with the tensioning of the membrane.
For a displacer, I use a small can, according to the "transferator" principle, since making nice round steel wol displacers don't seem to work for me either. (They look more like a bad hair day after winding it up, causing too much friction.)

Maybe I just too clumsy by nature to make projects like this ending happily, but I want to try one more time.

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[Jagang]

Nope, checked the hose for having an airtight fix on the cylinder, and it has, but it's as dead as a doornail.
It's not even trying.

So.. Either the diaphram must be too loose, or it's too large. But I've seen metronomes with full size diaphrams functioning?

[tibsim]

Hi! This so takes a lot of heat! Correct ratio if piston is 50% of the cylinder. Make the displacer out of fine metal wool that you loosen up so you can almost see through it! The gap between the displacer and the cylinder must be small! You can make a displacer box and put metal wool in it.

[tibsim]

Maybe, mistake is still that the circle of the balloon is small. Many work will make good result...