Making Model Gas Engines

Minnesota collector indulges in the joy of building and showing model gas engines.

Scale engines on display

Allan Severson’s scale engines set out on display on his trailer at a recent engine show.

Photo by Bill Vossler

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Many gas engine collectors begin their careers with small, common engines of one or two horsepower, and might in the future turn to model gas engines for some variety – but not Allan Severson of Blooming Prairie, Minnesota. “I actually started with the models,” the 62-year-old machinist says.

Allan grew up on a farm, where his dad had a repair shop, so he’d been working on different machines, including tractors, since he was 6 years old. “I’ve always had an interest in old iron,” he says.

After his dad bought a Breisch casting kit of an Olds engine in the mid-1970s, one of those interests became model gas engines. “My dad only had a lathe with a milling attachment to do the milling, so I did all the work on a milling machine I had access to at work, and made about half of his gas engine. That was a somewhat difficult engine, because it has a Lunkenheimer carburetor with all kinds of passages in it, and many people have trouble with that. It’s the worst part of that whole engine. After working on that one, it just exploded into what I’ve got today,” he says, which is about two dozen model gas engines, about half of which are finished and, like the real thing, run.

First time

The first model engine Allan built for himself was of a 25 HP Fairbanks-Morse. His father had gotten a casting kit of that engine in the high base version from George Scott of Outlook, Montana. “I kind of copied the castings from him, and built a low base out of steel, so it was totally fabricated. The flywheels are made out of steel plate and the base and cylinder are miscellaneous parts welded together and machined to look like the casting kit.”

Having made model engines for so many years, Allan says he sees a difference in the castings that come to him nowadays. “Most of them you buy from a casting supplier and the kit will come with all the castings, and a full set of blueprints. With the older stuff, the blueprints were not too clear and left a lot to be desired. But the later ones are nice. The point of the blueprint is to show how to machine everything, what needs to be surfaced off, where to drill holes, how many ring grooves are needed and where, what diameter the wrist pin is, and so on. The blueprint shows all the dimensions that a final-machined part must have, as well as their exact locations.”

He notes that you have to machine all the parts into the castings that are supplied, and for an example, you have to cut the valve guides, spark plug hole, or the igniter in the head, and the exhaust ports.

Though the crankshaft isn’t the most difficult part of the model engines to machine, Allan doesn’t like working with them. “I don’t know why. They’re not difficult, but I hate to work with them. They’re kind of flimsy and your tool for your lathe is hanging way out to get the throws for the connecting rod. Once I get started it’s not difficult, but it’s one of the parts I always dread.”

Some of the parts might take several days worth of work to get finished, like a cylinder, which can require multiple setups to get the cylinder bore, crankshaft bores and camshaft aligned. “There’s a fair amount of work required to get some of the cylinders and bases completed,” Allan says. “When working on an engine I try to set some goals. One of them is to do an average of one part a day. I will go to work early and try to accomplish this. It depends on how much time you’re allotted. If I work two hours on one day and all day the next day, I still want two parts done. Sometimes I will get several parts in one day, while others will take longer.”

The typical model has 75-100 parts, Allan says. “Essentially, all of them have to be machined. Some are simpler and some are more complex.” He used to get calls from people wanting help with the models or other engines, but he doesn’t get too many any more. “It seems like there’s less interest in the model engines nowadays. A lot of the people who were interested in them were elderly, and quite a number of them have passed on. There are a few in the younger generation collecting, but it’s fewer than it used to be.”

Which one next?

Allan says he doesn’t have a great deal of choice on which would be the next model engine to buy. “It depends on what’s available. I have all of Debolt Machine Inc.’s castings,” he says. “He runs a limited number of castings, maybe for two years, and when the interest in a certain engine starts to wane, he quits making them and no more of that one will ever be made again. He moves on to another engine.” Allan figures a couple hundred of each model might be made, when all is said and done.

Debolt’s first cast model was the half-scale Witte. “That was the very first casting kit they ever produced, and was made in a very low volume. Not too many people have that one. I actually have an extra one of these. Each of their engines has improved over time with the quality of the castings,” Allan says.

Instead of rough-cast models, mechanics kits of model engines can be purchased that only require assembly. “I don’t think about them until I’m making a certain part, and then I wish I had bought one,” he laughs.

The casting kits can be pricey, Allan notes. They used to start at $100 to $150 and can now run to over $1,000. “The last one I bought cost $699, but then I typically buy accessories like oilers, spark plugs, brass fittings, gasket sets and whatever they might have, so the total came to over $1,000.”

Allan says it depends on the casting maker as to which accessories might be available for a particular engine. If certain accessories aren’t available, Allan has to make them. “You have a print of what you need, then grab a piece of brass or steel and take away everything that doesn’t look like that part.”

He‘s got the entire Debolt series. “I buy his right away, because I don’t want to lose out on one. It’s my personal pride that I have all of them.” Some of his other Debolt engines include a Vaughan “sidewinder,” which has only one flywheel on it. “Instead of a regular crankshaft, it has a cheek plate on the side, which gives you the throw.”

One of his favorite engines is the Allman inverted, a design that dates to the 1890s, and another curious one is the Canfield engine. “That’s kind of a different looking one, and like most of my model engines, it’s a 1/3 scale. It has a water tank on top and a scavenger exhaust. The full-size ones were built in New York about 1903,” Allan says. Other engines include a Fuller & Johnson, a Perkins Windmill Co., and a Mogul model, which is a sideshaft and is screen-cooled.

The fastest Allan has ever made one of the engines was in one week, when he was at home to get things ready for his daughter’s graduation. “My wife would rather not have had me in the house at that time. I had just gotten the Allman engine, and during that week I machined it and put it together,” Allan says.

Shortly after his daughter’s graduation, Allan went to a show and took the Allman engine along. “People said, ‘You can’t have that one running. It just came out. It’s not possible!’” He was happy to show that, obviously, it was possible.

Loss of power

Allan says scaling an engine down to third-scale – which is what most of his models are, outside the half-scale Witte – really cuts down on the power they can produce. “If you take a 6-inch piston and make it a third scale of 2 inches, it’s a considerable size difference, just like scaling a 3-foot flywheel down to a 1-foot flywheel. It doesn’t seem like a lot, but there’s a massive amount of power loss that you get when you do that. You can put a pretty good load on one of those small ones and keep it going, but you don’t get a third of the horsepower of a full-size engine. You may get 10 percent or something like that. Part of that is because when you drop the piston from 6 inches to 2 inches, the area of the face of the piston is so much smaller, and that smaller size is probably how much the horsepower is dropped.”

Though Allan has the skill as a machinist to make his own model kit of some particular engine, he’s never been interested. “It’s never really appealed to me,” Allan says. “Maybe after all the work I did on Big Four tractors I‘ve been working on for myself and others, it has given me more skills on the patternmaking side.”

What Allan enjoys most is finishing a project, and getting the model engines running. “The Perkins and the Stickney are two of the finickiest engines I’ve got. The Perkins has a strange ignition system on it that kind of retimes itself once in a while. If it kicks back, it unscrews the cam that sets the timing. It unscrews, but never seems to relocate quite the same. The Stickney has so many places to lose compression that it’s tough to keep the compression up and keep it running good – the igniter off the side can lose compression, the piston rings or the valves.”

Many people show see his scale engines at shows think they are actual engines, and wonder what they would have been used for. “That makes me smile a bit, because it means you did a good job if they think they are real. But on the other hand, it kind of irritates me, because people don’t realize that I made them. I do have a sign that indicates that I made these engines, but people don’t always read it,” Allan says.

Engine joy

The joy of the model engines comes in several ways, Allan says. “They’re just so much fun to watch. I go to threshing shows just to watch them. They’re much more portable than full-size engines of course, and they’re intriguing because they are so small. I’ve sure made a lot of friends because of those model engines.”

From scale engines to Big Four tractors

Building model gasoline engines is doubtless a lot easier than building the huge engines of the Big Four 30 tractors, but Allan Severson has been involved in doing just that. The Big Four 30 was first manufactured by Gas Traction Co., of Minneapolis, Minnesota, about 1910. Allan and his wife, Harriet, are helping with the restoration of 11 Big Four tractors from all over the world, including building a complete engine from scratch. “It’s an effort that has gotten assistance from as far away as Australia and the Netherlands,” Allan says. Only 25 of the tractors exist, so the group shares information and parts with each other. “We end up being the central point for most of the parts being made.”

To get the engine right, he borrowed a Big Four 30 from the Hastings (Minnesota) Little Log House Pioneer Village Showground, and spent two winters tearing the engine apart, measuring and copying the parts. “We reverse engineered it, you might say. We made patterns using original parts or carved them out of wood, compensating for shrinkage during casting,” Allan says.

Cylinder patterns had to be modified, and then the castings had to be made. “We cast a new upper and lower crankcase, with every part of the engine brand new, the crankshaft, pistons, connecting rods, cylinders, manifolds – every part in the engine. Every part of the transmission was also cast new.

The process was much more difficult than could have been anticipated,” Allan says. “The cylinders were the worst. One foundry made some good parts, but the ratio of good parts to bad was really high [and] they wouldn’t make any more for us.”

A second experienced foundry made better parts in general, but struggled with getting the cylinders right. “The complexity of it, with the water jackets and valve chambers and so on. This particular cylinder is a headless design, so the valves and head are part of the casting. This means a need for more cores, and if anything moves or anything happens, you get a bad part. When you pour metal, gases build up,” Allan notes. They need an escape route, and often end up blowing a hole in the casting.

“Most of the casting used original gray cast material, while the crankshaft and some other parts were built of ductile cast, like modern crankshafts. Outside of the castings, everything else was done in house, including pouring the babbitt and machining. Everything in the engine was made new with the exception of a new-old-stock original carburetor and a used governor.”

Contact Bill Vossler at Box 372, 400 Caroline Ln., Rockville, MN 56369 •