This thread details my thought process, fabrication, assembly, usage, and improvements in making a twin jackshaft automatic transmission for small engines. SEE POST 40 FOR FINAL UPDATE AND SETUP Got the idea of making a 3-speed jackshaft. Anybody ever had one of those Rupp 2-speeds? I did not, but I had R/C cars with adjustable 2nd gear shift points. They worked well. The way the 2-speed work is by the use of a freewheel and a cent. clutch inside the 2nd gear. The motor pulls the first gear on the freewheel, and then when the jackshaft spins fast enough, the 2nd gear engages and spins the JS faster than first gear, which makes first gear freewheel. RC car company Kyosho made a 3-speed for their Mad Force. They combined the cam from 2nd gear and the FW from first gear, to make a middle gear. Thus, after the 2nd gear cam engages, it drives the JS faster than 1st making it freewheel, but not fast enough for 3rd to engage. As the JS spins up even faster, 3rd gear engages and forces 2nd to freewheel on the shaft. This could be adapted to motorized bikes. I would put all the driving gears on the crankshaft but there might not be enough room. Picture shows two cam ideas. Second one is adjustable with a set screw and spring weight. Using more than one middle gear of this type could give you an overall 4- or 5- speed transmission.. it would be heavy though. Of course, you'd only get engine braking in top gear. Thoughts? Would you buy one?