Reader's Scale Engines

| March/April 2004

Paul Brien's scale Young engine

Paul Brien's scale Young engine.

I built this model engine in 1999 from a set of castings and drawings Ted Young was offering at that time. It is a neat little engine of 1-1/2-inch bore by 1-7/8-inch stroke with jump-spark ignition. The cylinder and piston are both cast iron. I turned two grooves for rings on the piston, but I found upon assembly that the engine had such high compression (5.6:1) that I never have installed rings.

I bored the cylinder as near parallel as I could and I honed it with a brake cylinder hone. I then turned the piston to as near the cylinder bore as I could and still just push the piston through the bore. I used Comet cleanser as a lapping compound to get a close fit that would leave just enough room to maintain a film of oil. I have run the engine many times at shows and events in the last four years, and the compression has not decreased.

For ignition, I use a 9.6-volt 900MAh Ni-Cad rechargeable battery Radio Shack sells for radio-controlled cars. The battery is mounted in the engine base. I can check its status by turning the flywheel until the points are open. With the switch on, I place one probe of a volt/ohm meter to the hot wire connection to the breaker points and the other probe to any ground on the engine. I made two little brass connectors that plug into the battery's plastic connector, and covered them with heat-shrink tubing

The spark coil is from a junked string-trimmer engine, manufactured before the move to coils with a built-in solid-state circuit (eliminating the points and condenser). There is no way I know of to make coils with built-in solid-state circuits work on our engines that use a battery ignition.

The base is made from pieces of I-inch by 4-inch oak glued together using Elmer's wood glue. This method of construction makes it easier to make all the pocket cutouts for the battery, wiring, gas tank, etc., before the individual pieces are glued together. Handles across the ends of the base make it easy to lift the model, and I've found the one on the front to be essential when cranking with the flywheel against the engine's high compression.

Paul Brien , 4312 Lone Oak Road Nashville, TN 37215