Here is an entry level, beginner model engine that you can build with a small lathe and drill press. Of course, if you have more machinery, such as a small vertical mill it could be easier, but this engine does not require it. This design is based on small and easy to make aluminum castings! It is a scratch build, minimal purchased components and you wind up with a running model engine. There are six pages of drawings and text.
On a scale of 1 to 10 I would rate this engine as a solid 5, advanced beginner who is tinkering with aluminum sand casting. It is well within the range of a Unimat or similar small lathe, of course a small bench lathe like available from Harbor Freight would work nicely. It is not too complicated and not too many parts to make so it is a good entry level model engine project. It is spark ignition and two cycle and would make a nice model boat engine.
It is an easy to follow set of plans and if you are aspiring to build your own model engines, this is a great selection? Get this one under your belt and then move on to more sophisticated engines like the Wall 1 hp single air cooled or if you really feel ambitious, try a Wall 4 cylinder!
In our store we also are offering the book "model gasoline engines" on CD-ROM, (pdf) and, other model engine drawings sets, The MORTON M-5 drawings on CD-ROM and other model engine / hit & miss related items! We also have repair manuals for lots of small commercially built engines. If your interests run along history of model engines these items are definitely for you.