Hello again everyone. The other day a friend of mine asked me about using an o-ring instead of piston rings in a scale engine. I love the idea, and I use o-rings in most of the models I build.
Further, sometimes I install a cast ring in the ring groove below the o-ring. After the engine is broken in I'll pull the o-ring and install another cast ring, which gives it great compression.
The o-ring method will give you some piston slap as you are running only one 'ring,' and it is at the top of the piston. In my experience this hasn't caused any problems.
If you want to run an o-ring, here is the way I do it. First, fit the piston close to your bore size -just so it passes smoothly through the bore. Next, cut the groove you normally would for a regular cast ring. I have found that each o-ring needs a custom fit as they come in many different sizes, both in diameter and thickness. With the o-ring installed, you want the piston to fit snug in the bore since the o-ring will expand some.
Now, I know some of you are thinking an o-ring won't last for long, and you're right. The engines I have built (and those of some friends') with o-rings will generally run for about 100 hours before the o-ring fails. If you think about it, that's some serious running time over the course of a season.
One benefit of using an o-ring is you don't need a great hone job to seat the rings, as a smooth bore works best with an o-ring. Have you ever looked at the inside of a hydraulic ram? They have almost a polished surface.
Another great benefit of using an o-ring is you only need a small amount of oil to lubricate the cylinder. This helps to keep the spark plug from fouling out, and it also helps keep the model clean while running.
Of late, I have been using different oils in my sight oilers just for appearance. Ever try Marvel Mystery oil or transmission fluid (red in color)? Maybe chain saw oil (green in color) or even baby oil (clear)? I leave the oilers shut off, but looking as if they are open. I only let a very small amount of oil feed to the piston.
I've even tried using WD-40 in the oiler of one engine, just letting it slowly drip. The engine ran fine and - it seemed to me - perhaps even a little smoother.
These tips are for your thoughts only, and your fuel lines may vary. - Rusty Hopper
Have a tip you think other model makers should know? Send it to Rusty Hopper care of Gas Engine Magazine, 1503 S.W. 42nd St., Topeka, KS 66609-1265, or e-mail: firstname.lastname@example.org
Reader's Scale Engines
L. Gardner & Sons Scale
This is a half-scale L. Gardner & Sons No. 0 gas engine. The casting came from Alyn Foundry in England. The specifics are:
|Weight:||18 kg (39 lbs.)|
This engine was first introduced in the mid-1890s and remained virtually unchanged for almost a quarter of a century. The name Gardner is famous the world over. Robert Brandie 157 Don St., Bendigo, Victoria, 3550 Australia, email@example.com
Corliss Steam Scale
My engine is a 1/20-scale model of a 100 HP Corliss steam engine (sorry, it's not gas) that was used in a cotton mill here in central Texas.
The full-size engine is in good shape and was an excellent specimen to measure. I've worked on the scale for about two years making molds for the lost wax castings. The prototype is bronze, and I'm currently working on building one in iron.
I learned so much about building engines with this project that I don't know where to begin when it comes to offering tips. Perhaps Rusty could offer some suggestions.
I love GEM, keep it up! Maury Uebelhor firstname.lastname@example.org