To conclude this article.
I know there have been many failures with this engine over the years but a couple of modifications can make a mountain of difference. If any readers are contemplating a build, don’t hesitate, go for it…. The castings are available from Reeves of Birmingham.
Find a suitable aerosol deodorant can to make the displacer piston from. Either Steel or Aluminium. The Steel is much slower in heat conduction but a little heavier in weight. The hot end material chosen is the other major factor. In the original ME text it suggests Copper or Nickel alloy. Both these are good conductors of heat, sadly in the wrong direction. We need a concentrated spot, right at the bottom end but with poor conduction via the material. As stated above worn out shock absorbers make ideal hot ends with no risk of leaking air.
There’s two methods of fixing the hot end described in the ME text. The screw on method is the least desirable. Any heat will be directly conducted into the cold end. The use of a flange with studs and nuts with a nice thick juicy Silicone or Viton O ring between will greatly reduce heat transfer. And why so many studs, in the original text? I would suggest a maximum of 3, the smaller the better. It’s not a racing engine, an injured Gnat develops more power. No need for all those extra fixtures.
Many of the smaller, original Heinrici engines were actually air cooled. The cold end being just a tubular Iron casting. They worked very well. Because the replica cold end is made from Aluminium it will tend to absorb heat much more quickly so this is why a water jacket is essential.
Graham.