JEAN Tips on Building a Scale Wobbler

A 1/2-Inch Bore,1-Inch Stroke Wobbler
By Ed Warren
May 2005
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Ed Warren supplied these drawings to assist Gas Engine Magazine readers in building the scale “Jean” engine.
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Editor's note: Noted model engine builder Ed Warren created this wobbler engine especially for the readers of Gas Engine Magazine.

Ed loves to design and build models, and what follows is a list of tips Ed has compiled to make building "Jean" fun and easy.

Special thanks go to George Broad, former publisher of Modeltec magazine, who published Ed's book (now out of print), Home Made Steam Engines, Volume 1 - The Wobblers, in 1998. Ed supplied George the computerized drawings shown on the top of the opposite page, which George further refined for their book. Enjoy!

For those of you who don't have a reamer, there is another way to drill and ream a hole to the proper size; drill the hole 1/64-inch smaller and then go back through the hole with the proper size drill. Under most circumstances, when a hole is drilled with the proper size drill, it will drill oversize, making for a sloppy fit.

The bearing brass that goes into the cylinder mount can be held in place with thread locker. I let the bearing protrude a few thousandths of an inch to act as a bearing surface for the flywheel.

Starting with the cylinder mount, very carefully lay out the holes and drill them, being extra careful laying out the port holes in the bottom of the cylinder mount so they can be lined up with those in the base. I use brass for the bushing, and after it is pressed or glued in place, I drill an oil hole through the top part of the steel and down through the bushing. This is not shown in the drawing, but it runs better when oiled.

I do the cylinder next - it is important to square up the cylinder as close as possible so that when the holes are drilled there will not be any binding when assembled and running. It must turn easily, since these engines do not have too much power in the first place. The piston shown in the drawing is brass, but aluminum can be used if you use a steel cylinder. I cut it to length and drill the hole. The cylinder is an exception to the "reaming rule." I recommend drilling with the correct size drill first and allow it to be a little oversize. This is the first place to find the binding in the assembly.

The crankshaft can have flats on it to prevent raising metal from the set screw. On the flywheel, it looks a lot better if the recess is turned in on each side, or it can have equally spaced holes drilled in it, or both. There are iron flywheels available that look good, too. You can assemble the crank disc with either a set screw or thread locker, as well as the crank pin if it is drilled to a close fit. The pulley can be made of whatever material you have on hand. The groove must be wide enough to accommodate the 1/8-inch O-ring for the belt. The angle is not critical as long as the belt goes in far enough for a good grip.

You can buy a spring at your local hardware store for the engine assembly. If you put too much tension on the spring, it will prevent it from running. The engine will run in either direction, depending on which hole you run the air supply to. For the engine mount plate, the hardest part is drilling the cross holes for the pressure inlet to the engine. I used aluminum for ease of drilling. Carefully lay out the holes, paying close attention to the holes for the ports so they line up. Be sure to drill the correct hole for the pressure inlet. When tapping it, if you do the wrong one, it will run in the wrong direction. The holes in the corner are for mounting this whole system to the top of a pan large and deep enough to hold water for circulation.

I hope everyone enjoys this project as much as I have!

Contact engine enthusiast Ed Warren at: 11996 Gast Road, Bridgman, MI 49106; (269) 426-3596.


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