Lil' Bit, a Half Scale LTD Stirling

New 3/15/98

Last year I built 3 Low Temperature Differential engines from Jim Senft's book of the same name. Richard had made up a few sets of the main plates in a beautiful blue anodized aluminum, and had the Plexiglas rings and piston assemblies, so I had only the miscellaneous parts to fabricate. As in the fans, one copy went to the Machine Tool Club at DeKalb Tech, another to my son and the third resides with me. But, being a chronically dissatisfied model maker, I wanted a smaller version.

At last fall's PRIME, I was looking over Jerry Howell's offerings and noticed that he had made a half sized LTD, and was selling a "Hard to Find Parts" kit for the same. A few seconds calculation told me that I could not order the bearings for much less than his show special price, so one went home with me. Making the fans took up most of my time over the next few months, so it wasn't until late February that I got started.

In the meantime, Jim Senft had written an article for Modeltec magazine on his "Domino", a half size version of his N-92 engine. So, armed with Jerry's bearings, Plexiglas ring and displacer material and Jim's article, I made a few design changes and proceeded to make my own engine, which you see here.

The main plates are just over 3" diameter. The Plexiglas ring is 3" o.d. and 2.75 i.d. The power cylinder is .375 i.d. and just over 1" long. The flywheel and displacer crank shaft run in 3/32 x 3/16 ball bearings. This is a really sweet running little engine. I made a heat transfer plate per Jim's suggestion in his Modeltec article, and the engine will run over 5 hours on an eight ounce styrafoam cup of crushed ice! My cold hands will barely run it on a cold day, but my wife, Hazle - the one with the hot hands - can rev it up to over 250 rpm in less than a minute!