HOW TO: Ben Minors Guide to Breaking in a Nitro Engine

I and many others have had our struggles attempting to figure out the black art of how to properly breaking a nitro engine. Sure, you can always go for a short 4 gallon deal and have good power at first, but after just a few months of flying, power really seems to fall off. Recently, I discovered Ben Minors guide on how to properly break in and tune a nitro engine. Needless to say, it has drastically improved how my engines last and perform in the long run. I wanted to repost it here so as many people could learn from it as possible. Hope you all enjoy and successfully run your engines!

The key to a break in process is understanding that you CAN get away with just a few fairly rich tanks and then letting it rip. THIS said, engines treated this way never develop their absolute power capability because the fit of the ring and sleeve is never optimized through a more methodical, patient break in.
I’ll take a new engine a burn the better part of (at least half) a gallon in a rich hover. I’ll land every one in a while and let the engine idle for a bit. If I get bored, I’ll do some gentle circuits, but I don’t turn on the idle up. Head speed is at most 1450-1500 rpm. You needn’t shake the model to death running it too rich, but you know well enough what nice and rich means.

When I get to the next gallon, I’ll fly the engine upstairs. Gentle aerobatics are OK, but DO NOT load the engine hard. It’s wise to depitch the collective so you can get to WOT without lugging the head. You can’t set the high speed needle if the engine is loaded up with 14 degrees of postive pitch. Think more along the lines of 8 or 9D at WOT in FFF. You can add the pitch back later on. The needle will be set so that it’s just barely lean enough to be mostly “clean”, but it’ll still break rich on occassion. Now, here’s the trick: when an engine is just barely leaned in enough to run as I describe and as it progesses through break in, you’ll notice it get more rich than where you had it originally set. All you do then is lean the high speed a click or two to get the mixture right back where it was, IE just a bit rich. The engine will repeat this process over the better part of 2-3 gallons of fuel. It’ll “ask” to be leaned in just a fuzz every few tanks of fuel. During this methodical process, you’re optimizing the fit between the ring and sleeve, which has a big reward in power in the end. When the needle setting stops getting a bit rich every few tanks of fuel, you’re more or less broken in. Since you’ve been maintaining a slightly rich needle, you can tune more for maximum power at this point. Given the tremendous power that the HZ has, you’ll need to think twice about whether you really need to lean the thing in to the point it’s running as hard as it can. A bit a margin is good for engine longevity. At this point, you need to go back and fine tune the midrange needle to be just a few clicks richer than as lean as you can get it without any midrange cackle. Doing this maximizes midrange torque and response. If the midrange is too rich, you’ll be tempted to overlean the high speed to compensate. This SCREWS EVERYTHING UP.

If you do the quick and dirty break in method, you’ll never see these subtle changes in needle settings as the ring beds in. In some ways, engines treated this way aren’t being broken in; they’re being “worn” in. Fuel isn’t cheap, but these engines darn sure aren’t either. To me it’s worth spending the time and effort through 2-3 gallons of fuel to really get that broken in correctly, after which you’ll have a stump puller for dozens of more gallons before an overhaul is needed.

Ben Minor

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