Making Model Gas Engines

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

| June/July 2015

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

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.