earlwb

Well I try to keep the break in instructions more or less simple for people. Heat cycling the engines is nothing new, they were doing it many years ago with the Brown Jr, O&R, Forster engines, et cetera. This is where you run the engine WOT for a short time, go back to idle for a short time and stop the engine and let it cool off, and then repeat. The harder short run, helps seat the ring faster. But the harder WOT run is actually done still on the rich side with the engine four cycling. After a few heat cycles, I lean the engine out a little and repeat. Other than that it is quite similar to the longer explanation below.

Nowadays people just do not seem to have the patience nor the interest to break in a engine properly or even try sometimes. They want to fire up a new engine, adjust it and go flying at WOT, right off the bat. Unfortunately, you cannot do that with a ringed engine. ABC/ABL/ABN engines tend to be somewhat more forgiving in that matter, but I still see lots of people trashing those ringless engines still.

But technically it goes something like this, but I think many people's eyes will glass over and they won't do it like this.  But it does work good though. especially if you were planning on using the ringed engine for competition.  I prefer to use no nitro or low nitro glow fuel in the Fox engines, but people just tend to ignore me on that matter and go with the higher nitro glow fuels though.

I like to make my first run of a ringed engine just at the 2 to 4 cycle break but on the 4 cycle side and at full throttle (carb wide open. The thought process is that one needs to reach maximum cylinder pressure to drive the ring into the cylinder's cross hatch and at the same time keep the ring cool. It is known that at the 2/4 cycle point when the combustion chamber fires that the cylinder pressure is the highest other than at detonation. Also at this rich mixture setting the there is extra oil available to keep the ring cool. The ring needs this because the contact with the cylinder is not complete to allow the ring to effectively transfer its heat to the cylinder walls. One also gets a free cooling cycle (oil with no added heat) in the 4 cycle mode as the engine only fires on every other rotation.

Once the ring starts to show signs of starting to seat (that's another discussion) I start to thermal cycle the engine to take into account the change in cylinder shape as a result the thermal discontinuities in our toy engine designs, I pinch the fuel line to bump the rpm into the 2 cycle range then allow the engine cool down into the 2/4 cycle break point. I do this until I can see that the ring is half seated. With a 3x glass you can usually see where the manufacturing marks in the ring are wearing into the cylinder. When half of these are polished down the engine is ready for some sports flying. When I say half seated I mean that 1/2 the ring is thickness (height) is showing full contact with the cylinder. On the Fox 10cc ringed engines this takes about 36 to 100 ounces of fuel to get the engine ready for sport flying. It takes me about another 3 to 4 gallons before I can push the engine to my expected power levels.  During the initial sport flying I like to do a lot of Cuban Eights as I think this cycles the engine just about perfectly.