A Model Builder's Surprises


| April/May 1996



Tom Thumb half scale

Tom Thumb half scale.

HC 6, Box 4 Aitkin, Minnesota 56431

I restore tractors, old engines and some old machinery. My favorite part of my hobby is building scratch model engines. I've built hit and miss throttle-control, inverted side shaft and hot air.

I use mostly steel for my engines. I also use some brass aluminum, and some cast iron. I've made one pattern for a flywheel for our scale Waterloo Boy 14 HP. Ray Olson from Garfield, Minnesota, gave me tips on how to make a pattern. He also cast them for us. Bruce Lind-berg from Duluth, Minnesota, machined the wheels for us. The wheels were over 10 inches in the rough. Our lathe will only handle 10 inches. Bruce is a fine machinist.

I'm going to mention a few problems I've experienced, a few mistakes and some goof ups I've made, how they were corrected, and how the little engines putted away happily ever after.

I built a little throttle controlled engine that runs nice and smooth. We call it our little steaming demon. On hot days, on long runs, there is a little steam that comes from the hopper. We have to add water once in a while. I was a little careless when I built it. I put the governor shaft directly in line with the cam and the business end of the rocker arm. The solution was very simple: Put a little bend or bump on the push rod. The cam and the push rod are inside of the engine frame, so it doesn't show. I think this is the only engine that has a push rod with a built-in detour.

I wanted a side shaft engine. Building one fit our budget better than buying one, and a lot more fun! The side shaft engine I built is not modeled to represent any special brand. When I was assembling it I realized I may have made the connecting rod about inch too long. This would give it too high compression. I took a chance on leaving it that way. A timer and buzz coil was the type of ignition used. All the bearings are oilite, including the cam shaft bearings. Oilite doesn't conduct electricity too well, so the timing wasn't positive. It would fire late, even when the timing was set well before top dead center. By advancing the timer a little more, sometimes it would fire on time, sometimes late and once in a while early. When I advanced it a little more, the result was a bent connecting rod and a broken piston. I replaced the piston, repaired the connecting rod and changed the ignition to regular points and coil. The result was a nice running engine.