I will be breaking in a K&B .40 next week. I have read everything I can get my hands on about these procedures, including the manual that came with the engine. My question: Why do you break these in slobbering rich? I overhaul full size air cooled aircraft piston engines for a living, among other things, and know first hand that it is the heat that speeds the break in process. The full sized engines have iron rings with steel cylinders, from what I read, glow engines are constructed the same. When running slobbering rich, the cylinder would seem to me to run too cool, which would prolong the break-in process. Am I way off base here or what. I have heard folks at the flying field say that they run them hot and they break in just fine. I don't want to ruin a new engine. Any comments appreciated.
-Tom

Well, I guess I'l start. Running any glow engine too lean can and usually does get very hot. Things can warp like the piston which has happened to me. In the air when the engine gets too hot, you lose power and the engine may quit or you will land with the throttle full forward and nothing from the plane.

ok
When you break in the full size engines you don't lean out the engine right away until it goes too lean.
With full size engines the jetting is fixed and rich unless you change it so in effect they are running 'slobbery rich'. Or plenty rich anyway.
The key here is to limit the temperature of the ring. The ring is a little rough and so is the cylinder causing considerable friction heat. A rich mixture and extra lube in the fuel cool the ring (and other parts) allowing the parts to slowly mate. This and thermal cycling of the parts (thermal cycling changes the parts kinda like heat treating) break in a motor for best performance.

Heat is good (to a point) for an ABC engine while breaking it in. Heat is NOT good during break-in of a ringed engine. What you are trying to do is 'seat' the ring. This requires a lot of lube and as little heat as possible at first to do it right. I typically will run a ringed engine VERY rich for the first ~10 three minute runs letting it cool completely between runs. Gradually over the next ~10 three minute runs lean it out to just richer than full lean, letting it cool completely between runs. Yea, this takes a while, but it will make the engine last a LONG time and develop FULL power!

BTW, in the event you ever wish to use an old engine (pre ABC) it will require the same break-in as a ringed engine.

Thank you all for the insight. It is true that a full sized engine is to be flown at a full rich mixture setting for break in. I normally observe during flight tests, that cylinder head temps often reach 325 to 425 degrees. After about 40 minutes to an hour the cyl temp and oil temp begin to stabilize which signals cylinder break in. I guess I will have to train my brain to think differently, and note that patience is the key to engine longevity.
-Tom

An important thing to consider is that there isn't any pressurized oil in a model airplane engine. In a full size airplane engine the oil is pumped to all the bearings and under the piston crowns. Most full size aircraft engines also feature an oil cooler. The oil does more than just lubricate. In a model airplane engine the only way to regulate engine temp is with the needle valve. More fuel = more oil going to the critical engine parts. And to heap insult onto injury, not only does leaning out a model airplane engine reduce the amount of oil flowing through the engine, it also raises cylinder temps because of the leaner fuel mixture. A real double whammy.[]

Tom:

The advice above is great for a conventional two stroke with a conventional ring in a conventional steel cylinder sleeve.

The K&B "Ringed 40" does not have either a conventional ring or a conventional steel cylinder sleeve. It has a Dykes type ring in a chromed liner. The Dykes ring will not have any wall pressure to speak of run at a low power setting, and will take an inordinately long time to run in if done this way.

Put a 10x6 prop on it, start it and let it warm, then go to full throttle and peak the HS needle, then back it out to about a 300-400 rpm drop. Bring the throttle back to 1/3 to 1/2 for a moment, then go to full throttle again. When the engine reaches its maximum rpm back the throttle down again. Keep running the rpm up and down for the first five minutes or so, then go to full throttle and hold it. If the rpm sags repeat the high-low throttle for another five minutes and recheck the high speed. When it will hold high speed without sagging it's ready to fly, and be adjusted normally.

"Heresy!" I hear someone cry. Not so. The K&B 40 is a very special engine, I don't know of any other with the same construction. There are others with Dykes rings, other engines with rings running in chromed sleeves, the K&B 40 is an animal unto itself.

I have more than a dozen of the 40s, this method has given me excellent results and totally reliable engines.

Bill.

PS: The K&B 61s are NOT Dykes ringed, run them in normally. wr.

I have never seen a K&B .40 with a chromed cylinder sleeve. I have seen plenty of K&B .61's chromed, but never a .40. If there are some out there I'm curious as to when they made them.[sm=confused.gif]

Chuck:

Apologies, sir. I just checked an 8350, an 8360, and a 4011. All steel sleeves. Memory fault: "Senior moment."

The break-in method is still valid, I do the HP engines the same way as they are also Dykes ringed.

Bill.

That's OK, I've posted my share of incorrect information. Especially during those late-night-before-bed times when I check in here

"Let he, who has not miss-posted....cast the first cylinder sleeve".....

I recently posted some info about Schnuerle engines I got from a Website,
and I thought it to be Gospel..........wrong answer Kimosabe.....

Pass the "egg-wiping towel".....[sm=bananahead.gif]

Dave.

Thanks Bill, is there any secret to the make up of the fuel you use to break these engines in with?
Thanks again to all who posted
-Tom

Tom:

The only secret to the fuel is no secret at all. It's castor oil.

You can use all castor or a blend with synthetic, just be sure you have at least 3% castor, preferably 4 or 5% in the mix.

I.m lazy, I just use Omega fuel as delivered except in the Cox and iron pistoned engines.

Bill.