Name That Motor!

 This little homebuilt gem resides in the Orchardville fire house, and is used for parades and odd jobs.  When I first saw it, I asked the chief if it was a _ _ _ _ _ _ _ motor, and he had to know how I would know that.

Before small and medium tractors were common, home craftsmen would build their own using one of these small four cylinder engines, and I have seen others like this tractor being used to plow snow and performing garden chores.  I've been looking at old junk for a long time, I guess.  Leave your best guess in comments, and I will post the answer in comments Thursday night.