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Excellent work. I'm impressed.

Thanks so much Matt. I did wonder about the copper PP cylinder. I didn't think wear would be an issue because of the graphite piston (and its only a toy, not running intermittently). But hadn't considered the expansion. I'm doing my best to come up with a modular design that is easy to swap parts in...

I was thinking 30mm diameter displacer with 30mm stroke. Displacer cylinder being 60mm of stainless and 30mm of air cooled copper. Displacer piped to nearby power cylinder. Cylinder being air cooled copper with a 24.3 mm graphite piston and 30mm stroke. Each side will be on seperate frame to try and...

Thanks Matt. I was assuming the rules were derived from Rizzo but it may have well been Senft. I have not been able to source any of their works yet so do not proclaim to have read them. The "rules" I refer to are: 1. The length of the displacer chamber = 3 times its diameter. 2. The lengt...

I'm designing up a basic gamma using what I believe are Rizzo's "rules of thumb". One rule is that the swept volume ratio displacer:power is 1.5:1. Knowing my power swept volume its easy enough to work out stroke and piston diameter. However there are infinite variations obviously. What sh...

I simply buy an aerated cement building block from my local hardware store. In Australia these are marketed under the brand name "Hebel". Once you have the brick, simply hack off a chunk (hacksaw or handsaw makes light work of it) and start shaping. One brick will supply many many pistons....

I've been experimenting further with an aerated cement (hebel) displacer and had good success with the following. I rough out an oversized piston from the aerated cement. I then bore a hole down the centre at about half the size of the final required diameter finishing about 10mm away from the hot e...

I'm just watching and learning with interest. Congratulations on an impressive looking creation. Beautifully built. I look forward to the day you "crack the code" and we see it spinning.

The displacer is 16mm x 40mm diameter. Which I have now just realised doesn't line up with recommended ratios. Maybe the designer who drew the plans had a reason. I covered the Hebel piston in a muffler paste tonight. I heated it until the paste hardened then lightly sanded to smooth everything back...

Hebel is a brand name. It is (as you have tried) foamed/aerated cement. I agree with the crumbling potential which is why I thought of a heat paste coating. The first iteration I impregnated with superglue. Although the cold end was fine the hot end vaporised the glue. I also tried the kneaded high ...

I thought I'd try and make a hebel brick displacer piston. My thoughts being it was relatively light and insulative. Surprisingly it worked very well. I question how well the hot end will fare but I'm thinking of coating that with JB high temperature paste. I've only run it for a few minutes so far....

I have a 3D printer and can use CAD so I'll give it a go. I have just tried making a displacer piston using JB Weld high heat putty. I haven't attempted to machine it yet as its still curing. That adventure was far from perfect so far. I'll get some 2 part JB and give your system a try.

Thank Vincent. Do you make them hollow some how or are they just a chunk of epoxy machined to suit?

I'm proud to report I now have a running engine. It will only run on a little hand held propane burner at this stage with the aluminium disp!acer piston. It runs much better if I put the wooden displacer piston in but it can't handle the heat and begins to burn. So the next step in the journey is to...

Thank you so much for your input Tom. You have educated me no end. I understand the basic principles but once we delve deeper into the thermodynamics I'm lost. Although I still haven't got this engine working yet, I refuse to be beaten. I just today finished lapping a new power cylinder (mild steel)...