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Nitro engine break-in

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Breaking in a nitro engine is part of what decides its performance, tunability and life. In recent years nitro engines were broken in thorugh a series of idled out tanks of fuel. Recently 2 methods are mainly used. There is what is considered the "heat cycle" method of break in and then the gradual increase in thorttle input through a series of tanks.

Some manufacturers like Traxxas claim you must use their break-in. This is not completely true, while these break-in methods usually work well, it is not the only method you can use. Note that these manufacturers will usually void your engine warranty if you use another break-in method.

The "Heat Cycle" method of break in is where as soon as you engine starts place it on the ground and begin running it in an empty paved lot for about 2-3 minutes at a time. Make sure it is tuned slightly rich and that your temps are about a normal day temperature of 200F/93C. After your 2-3 minutes is up shut the engine off, set the piston to BDC (Bottom Dead Center) and let it completely cool. Once it is cool start the engine back up, continue doing this cycle until you’ve ran around 15 minutes or so, making sure to place the piston at BDC each time it is shut off. After you have hit the 15 minute mark bump the running time up to 3-4 minutes. Start varying your RPM, and temperatures in the 200’s (ca 93C) is perfectly normal. What this does is create heat cycles on the components without adding incredible stress that could be imposed on engines when they are very rich and cold. After cycling the engine using this particular method for about 20-25 minutes you’ll be ready to finish fine tuning.

Wide Open Throttle MethodEdit

To use the wide open throttle method, the engine should be tuned extremely rich. Before starting the engine for the first time, wrap the head in a few layers of Aluminum foil, or layers of a sock. Use natural fibers socks like cotton or wool - artificial fibers could melt. Either have the car on a starter box or a piece of wood so the wheels don't touch the ground. Preheat the block of the engine to ~200F/93C, then start the engine. Pull the throttle slowly to wide open throttle, making certain the engine does not clear out. It should be 4-cycling {fireing every other rotation} and the wheels should barely be turning. Add heat to the engine with the heat gun to keep the engine over 200F/93C. Run through the entire tank and let the engine cool with the piston at bottom dead center, otherwise it could get stuck as the cylinder contracts. Repeat this process four times, then remove the foil and lean the high-speed needle so the engine is only slightly rich. Run gently for a tank or two, then tune for performance.


ABC break-in in the car 

Set the main needle according to the manufacturer's specifications (e.g., 2 to 3 turns counterclockwise from closed). Open the idle needle several turns so the engine shuts off when abruptly throttled back.  -Start the engine  -Advance the throttle to 1/2. Listen for 4-cycling. Lean the mixture to a rich two cycle operation.  -Run the car in a 100 foot diameter circle or figure 8. Keep the throttle at 1/2 and listen for 4-cycling. Don't let this happen! If it does, immediately lean the main fuel needle a little at a time until the engine produces a clean, steady 2-cycling sound. Run your car in a cicle/ figure 8 for about 1 minute. When the minute is up immediatly check the head temp.  Keep a log of run time, head temp, estimated rpm and your perfomance comments.  The goal is to keep the head temp. at above 200 degrees F. and less than approximately 230 degrees F. If the head temp. is less than 200 degrees F. lean the high speed needle slightly, and try again after the engine has completely cooled. When the engine stops, using the fly wheel turn the piston to BDC.  -Perform the 1 minute run at least three times while you adjust the head temp. by "tweaking" the needle valve as needed.  -Now run the car around for 2 minutes at least twice. Remember: 1/2 throttle and no four cycling. Same game : check head temp., allow it to cool, record data.  -Don't be tempted to open the throttle wide! The mixture settings will probably be all wrong for wide open throttle(WOT)(. There is plenty of time for that later.  -The rest of the 1/2 throttle break-in runs will be 3 minutes long. When they tottle 35 minutes(minimum), you have successfully heat-cycled your engine and break-in is properly complete. If you like you can run it another 10 minutes or so it won't hurt.  -Tune the engine for WOT and idle operation.  To read " Super Engine Tining" by Steve Pond go to ( ) 

Heat cycling for stress relief  Stress relief is accomplished by repeatedly heating and cooling the engine-short engine runs followed by complete cooling repeated many times. ABC engine break-in involves such heat cycles, betit is not the same proceedure as is used for non ABC engines. 

ABC break-in the inside story  Abc engines require a shorter break-in (heat cycling) than engines of the past- less than 45 min. for most. To attain and maintain maximum power levels, however, requires adherence to an entirely new set of break-in rules.  The primary objective of ABC break-in is to maintain the delicate top of the piston pinch zone while allowing the internal engine components to heat cycle with some minor smoothing and allignment (crankpin, wristpin, rod journals, etc.). 

Here is how this is achieved:  FUEL- Use the same fuel for break-in as you will for normal operation. If you break-in your engine with low nitromethane fuel, e.g., 5% and then jump to 20% for actual running, the piston / cylinder fit will be too loose. Five % nitro doesn't generate as high a combustion temp., so the cylinder won't expand as much, and the pinch zone will wear more than if the cylinder had pulled away farther, as it would with the hotter burning, higher nitro fuel. 

2- vs. 4-cycling operation  If you run a 2-stroke engine then you have heard of 4-cycling. When a two stroke engine is operated very fuel-rich or at somewhere below 1/2 throttle, it begins to fire on alternate crankshaft revolution. As the mixture is richened at wide open throttle, the ehaust sounds like this as it breaks from 2-cycling to 4-cycling: " RRREEEAAAHHHHHHH."  As the throttle is reduced to about 1/2, the exaust sounds like this, as it breaks from 2-cycling to 4-cycling: "RRRRREEEEETAT-TAT-TAT-TAT."  With both examples comes a simotanios loss of rpm with the change in exuast sound. This is 4-cycling. Learn to avoidit. Because the ABC-type engines were originally designed as WOT racing engines, their pistons and cylinders operated happily. Today, ABC engines are also expected to idle and throttle reliably. Unfortunatly this allows them to cool excessively, especially below 1/2 throttle, where poor cylinder scavenging (clearing) causes them to 4-cycle and wear away the critical pinch zone as the piston sleeve cools and tightens around the piston  Throttling is a necessary phase of running nitro engines in cars, so you can't simply eliminate it from your routine, but do not allow the engine to 4-cycle during break-in. Afterward, when engine components have been stess-relieved and bedded in through heat-cycling, the wearing effect of 4-cycling will be minimized. 

Tight ABC piston/cylinder assemblies  Some new Abc-type engines are so tight at TDC that for the first few times the engine is cranked over and run, the possibility exist of damaging the connecting rod, crankpin, and piston. To avoid this, preheat the cylinder and the head with a heat gun or a hair dryer. This preheating expands the piston sleeve, and that minimizes the potential for stress on all the engine components during initial startup.

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