A Model Builder's Surprises

Tom Thumb half scale

Tom Thumb half scale.

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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.

I'm sure the oilite bearings were the problem. The current could not reach the ground without traveling through the bearings; with points they are grounded to the frame.

We usually travel to Texas once a year to visit our daughter and family.

The oil field engines interested me a lot. Of course I had to try to build a small version of the engine and pump. This was done about 1984. The engine ran trouble free for four or five years, about nine shows a year, four to nine hours a day if it didn't rain.

The engine had Lauson engine points, a car coil and condenser. After a few years of running it would take a notion to 'ping' fire early, then run normal for awhile, just ping every few minutes. It continued to get worse. Sometimes it would fire so early it would stall the engine. I checked all the wires with my meter; wiggled the wires to see if I could find a bad circuit. No luck! I tried a new set of Lauson points, which helped a little for a couple of shows, but then it went back to its old tricks. We happened to have a few extra sets of points bouncing around in the glove compartment of our Ford truck. I converted the engine to a set of flea market Ford points. Then it ran like it should. I never did find out the cause of the occasional premature ignition.

I've got to reminisce a little. In 1929 we moved to Woonsocket, South Dakota. The farm had a windmill, but even in South Dakota the wind doesn't blow all the time. During the drought years, the water table must have been very low. Pumping water by hand was very difficult. My six-year-old body could hardly pull the pump handle down. My father bought a used IHC Tom Thumb and a belt driven pump jack. The little dependable Tom Thumb was used for other light jobs, too, like running the grind stone fanning mill, etc.

You guessed it! Another engine story coming. A half scale IHC model Tom Thumb 7 inch flywheel, 1 inch bore and stroke building went good. No bad mistakes, goof-ups or problems.

Start up time was when the problems started. It would run for a while but wouldn't keep running unless I would squirt a little extra oil in the mixer. I removed the cylinder. Machined it over-size, took a section of 1 inch hydraulic cylinder that was factory honed, turned down the outside to fit the engine's cylinder and used it for a sleeve. Then I machined piston number two. I put two ring grooves above the wrist pin and one ring groove below the wrist pin. Then I put in a new set of rings. The sleeve did not help. It did not run any better. It had to be the rings or the piston. The oil felt a little gritty when I removed the piston. The rings showed too much wear for a couple of hours running. I machined piston number three, this time just two rings above the wrist pin. Then I ordered new rings from another vendor. I installed the new piston and rings, for the third time! It started and kept on running with no extra oil. It has been displayed at many shows the last two summers. We pull a scale pump-jack and pump that pumps water. Just like the 'not so good' old days, the problem was bad rings.

Late summer 1995, I was thinking about building one more model. I could think of two good reasons why I should. Number one, I enjoy building them. Number two, I bought a new milling machine and rotary table that I needed a lot of practice on.

I decided on a 7/16 scale Associated Hired Man, or a reasonable resemblance of one. The bore and stroke of the original is 4'x5'. Scaled down on the model it would be 1 x 2.2. I went 2' stroke. A little less displacement and   lower compression makes for a smoother running engine. If you wonder why I decided on an odd scale like 7/16, I had a few leftover parts when I built the IHC Tom Thumb. We still had number one and number two piston, a bunch of brand new 1 inch rings, crank shaft material that fits the 7/16 scale Associated, plus a 1 cylinder.

Building this engine was almost without problems, except for the head. I used one inch thick steel for a start. Machining the head is mostly drilling for the valves intake and exhaust passages. In this case, a spark plug hole.

I was doing real well until I took the head and matched it to the block. It was quite obvious that I had drilled the valve chamber on the wrong side of the head. This would put the valve stems and springs inside of the cylinder. I made two nice little steel plugs inch thick that fit snugly in the holes that I drilled on the wrong side of the head. My intentions were to weld them in. At this time I have to mention, my 'good glasses' were sent back to the factory for repair. I was stuck with my old glasses that were not good for close-up work. I thought if I was very careful I would be able to weld the plugs in place. On my first attempt I succeeded in welding one head bolt hole shut, but I did get the plugs welded on one side. I cleaned up the weld slag. I decided to completely cover the head with weld. By that time my 73 year old eyes began to focus a lot better. This time I was successful. The weld machined up nice, and I got the valve chambers on the right side of the head.

We still needed a home for a 10 mm spark plug, so I carefully drilled through the top center of the head. This is the last 'oops !' I just nicked the exhaust passage so the plug hole and exhaust were connected. I sealed this goof-up with a brass plug well riveted in, and smoothed out, then changed the spark plug position. It is located on the edge of the head, similar to the location of the spark plug on a Fairbanks-Morse dishpan flywheel engine.

The little engine survived all of its head surgery. None of the scars show it is covered with bright red paint. November 10, 1995, with my wife, Mary, sitting in the cheering section, about 15 or 20 minutes of tinkering with it, the little Associated was running on its own!

The good optician fitted me with a fine pair of glasses, so now I'm able to read fine print and should be able to see where I'm welding.

I plan to build one more engine next year. Maybe 1 inch bore, 1 stroke, about 5 inch flywheels. I just happen to have some material around my shop that can be used for an engine that size.

I have to thank my wife and best friend for 49 years for her support. She enjoys the tractor and engine shows and also helps care for the tractors and engines. She keeps the camper well stocked with food and supplies. She deserves many more red roses than I bring her. Thanks, Mary!