Burt's No. 3: A Homemade Engine

A scale homemade engine built not once, not twice, but three times to get it just right.


| October 2005



Burt's No. 3 homemade engine

The title "Burt's No. 3" comes from the fact that Kenneth Burt must have fabricated each piece of this engine at least three times.

The title "Burt's No. 3" comes from the fact that I must have fabricated each piece of this homemade engine at least three times - some as much as five - before I was happy with the results.

First off, I'm not a machinist and I haven't worked with metal much, but I do have some interest in metal fabrication. I got interested in building a small gas engine after making several Pennsylvania oil field models, mostly of wood.

The Cylinder

The first piece I fabricated for "Burt's #3" was the cylinder. I turned it from 2-1/2-inch solid aluminum bar stock, and had no trouble drilling and tapping the size 8-32 holes. The outside of the cylinder was undercut to form the water jacket, and a steel tube 0.075-inch thick was pressed on with an O-ring on each end for a watertight seal. Water enters the 1/4-inch copper tube on the bottom and exits on the top. I drilled a 3/8-inch hole for the cylinder opening, then enlarged it to 3/4-inch. A boring bar was used to enlarge the opening to nearly 1-inch and honed with a brake cylinder hone to a good polish for the piston O-ring that I first heard about in Gas Engine Magazine. Near the center and top of the cylinder, I epoxied a 3/16-inch copper tube with a 1/16-inch opening into the cylinder for lubrication. It is not in the area where the O-ring travels.

The piston is made of aluminum with three ring grooves: The compression ring is the largest of the three, and the two smaller ring grooves hold oil rings. The engine is nearly vibration-free until approaching 3,500 to 4,000 RPM.

The Crankshaft

My first attempt at fabricating a crankshaft was a catastrophe. I didn't use near enough metal, and set screws were a waste of time. The second crank wasn't much better, either. The third and final crank with a 1/2-inch journal diameter and 3/8-inch rod for the main shaft were pressed in the web and dowel pinned. The 2-by-2-by-1/2-inch webs give a nearly balanced crank. I am quite satisfied with the 3/8-inch, but would go for 1/2-inch if I were to build another.

It appeared to be quite rigid, but was undercut for welding. I took it to an auto repair shop to be MIG welded. The welder was unhappy with the smoothness, so I asked him to get enough weld on so it would clean up in the lathe - this turned out okay. The welder thought the crank web was made of inferior material. After machining and polishing, I milled out the main shaft to allow room for the connecting rod.