Using the Westbury reference as a design guide, here is my test mule made from bits in my "scrap" box. The cylinder is a piece of DOM tubing 3" OD x 1.5" ID bored and honed to 1.75". Stroke is 3.5" with the exhaust port opening at about 40% of stroke from TDC. Ignition is with points, coil and a condenser. I added a 1/8" NPT port for a hot tube later on. The frame was made on my CNC router/mill using CamBam for CAD. Everything else was designed/fabricated using pen and paper to get the crank and rod clearances correct. The mixer has a flat-faced valve with 6 holes in the mixer body; five for air and one smaller hole for propane fuel. The flywheel is a spare casting I had lying about which is GiB keyed to the crank. The exhaust valve has provision for adjusting the spring pressure to see how that affects running. Both valves have 1/2" heads. After a few pops and spurts, I richened up the fuel to air ratio by blocking off one of the mixer intake holes. Surprisingly, it took off and ran as in the video. It still needs some crank counter weights as it is a bit "hoppy" on the bench. I'll perform some finish work in the next few weeks to pretty it up with a more substantial base and a bit of paint. Here is a link to the video:
https://rumble.com/shorts/v7gish6
Myrickmachine@gmail.com
7 Oct 2026, 13:57Log in to see this image





Graham.