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This is always an interesting topic with 2-strokers.
I have been told that each engine technology/construction requires a different style break-in, makes sense to me.On Cox .049s it seems if you break them in slow, they run slow. With these engines I was taught to run them fast, but rich, meaning a small prop and a 4-cycle. I was also told it was more important at first to get several heat cycles to “normalise” the metals rather than focusing on getting run time initially.
In practice, my best engines are a result of doing 5 two minute runs with the plug clip on, a 5×3 Top Flite wood, and sloppy rich, so rich that if you pull off the clip it will die. I let the engine cool off completely between runs. Next, I run it without the plug clip connected after starting, but rich. After 5 runs of a couple minutes each, with cool-off rests, I pinch the fuel line while running for short lean bursts, then let it go rich again. Next, I begin to lean it to the point of it cracking into a 2-cycle and if it holds the setting without sagging, I pinch the line for more lean bursts. By this time, the engine typically will have about 45 minutes on it (9-12 runs). Unless you have a really tight fit, it is ready to be run leaned down at this point.
Once it holds a lean setting for several 2-3 minute runs, I then go to a 6×3 and see if it will hold without sagging, then take a tach reading. Any .049 NOS engine that will turn up a 6×3 over 17,500 is a monster. I would much rather have that than 19,000 on a 5×3…propellor efficiency rules!
What was weird for me was “soaking” my Norvel Rev-Lites bores with castor oil and spinning them over cold as part of the break-in instructions…but it worked!
Your COX experience mirrors mine, and all the folks I have flown with over the years. Steel piston running in a steel bore.
I use the same procedure on the new Nos Gas engines I have broken in recently. These were OS MAX .19, K & B .19, .201, & .23. All these had new pistons and cylinders.
Fast short runs, sloppy rich mixtures short but high pitched props. Indeed, on initial runs, I can hold the cylinder with thumb and forefinger without getting burned.
I have only run one Norvell, and it was an AME ABC engine. No mention of soaking in castor. This one was ready after about 4 bladders on a flying prop with 35% nitro.
That would be due to it being one of the early models, chromed bore. The later Rev-Lite series had a dark grey anodized cylinder, they claim the bore being anodized makes it like ceramic. On these, they have you soak the bore with castor.
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