WOT BREAK-IN

Idling an engine and letting it run slow, 1/4, 1/2 throttle is incorrect. You want Wide Open Throttle after it warms up. YES Wide Open Throttle, even when it is brand new. This is in order to bring the engine up to temp. and fit the sleeve to what it was designed to run at. Anything less, and you are just leading your engine to an early death.

Yes, running at WOT slightly rich, but not 4 stroking rich is the proper way to do it. Here is some further explanation of ” the way”, and why it is the proper way.

As for break-in, there is a whole lot of misunderstanding about this basic engine operation.
Although we use the term “break-in”, by its wording alone it is misleading, because people wrongly assume it means to slowly and gradually bring an engine to tune by idling tanks of fuel, but you will see why this is incorrect and unnecessarily wastes fuel too!

It will take some time to convince yourself to bring a new engine to WOT, but when you start to understand it and why it is correct, you will realize just how many people are completely breaking the engine totally incorrectly.

It’s important to learn the theory about how these engines run ( 2 stroke ABC, ABN, AAC), and how to break them in, especially because I see WAY TOO MANY people using the wrong procedure of idling many tanks of fuel through the engine. That is unnecessary and damaging.

These engines use a sleeve around the piston to make the seal (piston doesn't have a ring) and it operates properly only with sufficient heat so that the sleeve can expand to its designed operating size and fit. All engines will be tight, especially when new, so on the initial runs, you want to have it get up to temp, so it can run how it is was designed to. By idling tanks and tanks through, overly rich and cool, the sleeve just wears MORE against the piston because it is not hot enough to expand to its operating size. And by doing that you are prematurely wearing out and ruining your engine. The piston/sleeve is designed to operate at running temps. Not doing this by running cool and rich on the bench leads to premature wear. By idling away tanks of fuel I GUARANTEE you are doing more harm than good. As long as the engine is warmed up first, you don’t have to drag out bringing it up to temp when it is brand new. It wont hurt or damage the working parts. These engines are very simple 2 stroke machines. They do not have extensive moving parts such as valves, cams, lifters, springs, etc. (like 4 strokers) so all this extra gentle, rich, cool operation is completely unnecessary (and worse it’s harmful). HOWEVER, the sleeve around the piston can be a delicate thing to maintain, and it is not forgiving of improper treatment, and improper treatment of a piston and sleeve is running it at a temp it is not designed for. (either too cold or too hot, both are just as detrimental) Most often this is done by running it too rich which makes it too cold because the rich mixture doesn't generate enough combustion heat for proper sleeve expansion. Just as damaging can be an excessively lean run. If it is run overly lean for any length of time it will destroy the sleeve. (that is why fuels with castor oil as part of the lube mix are very good because they tolerate the too high heat of a very lean run and will help to save the sleeve if it is not run too lean for too long (but avoiding a lean run is essential when you know enough about engine tuning to avoid it).

Running a 2 stroke engine slow and rich makes it '4 stroke' which means it fires every other revolution, and that generates even less heat. It causes damage and wastes fuel as well. Most important is to 'heat cycle' the engine at least 10 times to relieve the parts of manufacturing stresses. HEAT CYCLING REALLY IS WHAT BREAK IN IS ALL ABOUT. (I even think break-in should be called “Initial Heat Cycling” instead so that people understand what and why they are doing it.)

Run the engine in a bench for 2 - 3 minutes at full throttle (yes, WOT, don’t baby it), after briefly warming up of course, and then shut down and repeat after the engine has fully cooled. Let it cool down completely. Heat cycling is the name of the game. You want it to come up to temp for a brief time, and cool down and repeat. After shutting down, adjust the flywheel so that the piston is at BDC (bottom dead center) so that it does not get stuck in the contracting/cooling sleeve, as can often happen. (If the piston should accidentally get stuck in the sleeve, preheat the cylinder to free the piston from the sleeve.). Follow this procedure for at least 3 tanks, then put the engine on the car and do another 3 tanks at the track to finish Break-in, leaning the engine a bit after every run

During these initial runs YOU WANT the temps to be at least 90° C but not above 109° C.
After break-in, running temps above 109°C is fine. In fact new generation nitro engines perform best when run at 120°C – 130°C. Below those temps they are less efficient and less powerful.
However, going by the mixture is more important than trying to measure temp with heat guns, etc. which you may wind up doing inconsistently. The mixture setting on the High Speed Needle is critical in the first runs. It should be a rich and not lean setting. However it should not be so rich that it 4 strokes.

Also, to start a brand new engine it is very worthwhile to preheat the engine with a heat gun or hair dryer if it has a very tight piston/sleeve fit and you are having trouble turning it over to start it up. This will expand the sleeve some, and when you turn it over the piston will not excessively rub, or even get stuck in the sleeve (as sometimes can happen). Preheating really works well. You do want to run it on the rich side, but you want it to come up to temp also, just not more than 2-3 minutes in beginning runs, in order to keep temps around 109°C. Listen carefully to the exhaust noise or ‘note’, as you do not want it to be ‘4 stroking’. If it is, it needs to be leaned slowly until it runs 2 stroke. You can tell it is 4 stroking if it is very “boggy” and “hesitant” in acceleration and running. If it is making that “burbling” sound then it is 4 stroking which means it is running too rich and therefore too cold.

Everyone thinks they have to run it super cool and check to be sure temps are low. That's not what it is about. The reverse is true! Cool operation is damaging operation. Little, if any, break-in will occur unless it is heat cycled properly.

The manufactures can’t make a piston/sleeve turn over smoothly at room temp, because when the engine runs the sleeve will expand and there will be no seal at operating temp. See how that makes sense?!

So preheat it if necessary and don't run it cool, and heat cycle it, and you'll be good to go! After you have done this several times then you can gradually lean out the HSN to get best performance, but it should then be richened up just rich of peak to ensure it lasts long too. Running it at max peak rpm will lead to the shortest useful life of the piston and sleeve. If racing that is fine but if you are just playing you may want to run just a little richer than that peak setting. After the HSN is set then it is time to set the low and/or mid range needles and idling setting.

I see a lot of people idle the engine for a tank and then they let it cool off thinking that they are "heat cycling" it. However, because they are not running it up to WOT it is not generating enough heat to be of any use to a break-in/heat cycle. So, inadvertently by idling they are just letting the engine sleeve and piston wear away from the cold tight fit that they are allowing to happen when idling away on the bench. Research has shown that basically no break-in effect takes place AT ALL unless the engine is allowed to come up to operating temp for 2 minutes. So if you are idling away and then let it cool there is zero break-in/heat cycle benefit. But if you want to wear away the sleeve and piston fit then idling will definitely do it for you.

As you’ve read, there are a number of reasons why I disagree with conventional break-in methods, but the most important are:

1) Heat cycling- rich and slow means not enough heat.

2) Aluminum connecting rod stretches. If you break in a motor with aluminum rods at low RPMs, and begin the mating of the piston and sleeve (since r/c motors don't have rings), then when you go to WOT the piston actually goes higher than it did during break-in and begins to destroy the surfaces not used.

I hope this is helpful!!

AFM

P.S. If you want to hear it from him, read Dave Gierke’s article in the January 2002 issue of “RC Nitro” magazine! "

This is what Rody Roem from RB Concept says for Break-In

Before you start to Break-in an engine on the bench, I suggest you cover the cooling-head with something, so the engine heats-up properly FOR ONE TANK at idle (without the cover the engine will stay too cold).

Then start the engine and let it run rich at full throttle with or without the cover (depending on temp):
2-tanks at about 80°C.
Then 2 more tanks at 90°C.
Then 1 more tank at 100°C.

After this your engine is almost run-in, however you need to finish the rest of the Break-in in the car for about 2 more tanks tuning your needles for max power and you are then ready to go.

With the engine at full-throttle, you are sure that the idle needle is not in front of the spray bar, so you are running the engine really on the setting of the main-needle and you’re also sure the engine will run rich. Also more fuel/air will go through the engine at full throttle so there’s better lubrication.
DON’T FORGET TO COOL-OFF YOUR ENGINE COMPLETELY AFTER EVERY TANK.

Rody Roem
RB Concept Engines