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Old 08-22-2009, 07:24 PM   #1
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Default this should intrest you guys.

130 to 150 is too cold for a nitro engine that has no piston ring (that would be all car engines BTW). I just finished writing an article about the accelerated wear that can result from running an engine in very cold conditions, and from excessively rich fuel mixture.

A piston sleeve is tapered so that when the engine warms up, the hotter temps near the top of the sleeve cause the sleeve to straighten out, at least in simple terms. If the engine is run too cold, that expansion never happens, which causes the piston to wear quite a bit faster than it normally would.

For example, a piston in a competition engine is usually about 0.0005 larger than the bore at the top of the piston sleeve. That means the piston physically sticks in the top of the sleeve until the engine is broken in, and then the piston is MAYBE .0005 smaller than the bore after burning 5 to 6 gallons of fuel.

The difference in expansion between running the engine cold and hot is about .0025. That means the bore in the piston sleeve is two and half thousandths smaller when the engine is running very cool. Over time, that means that you're wearing away an extra .0025 from the diameter of the piston.

When an engine is new, you push the piston through the sleeve. It gets stuck. But, after you run a season of freezing temps, the piston will drop right through the sleeve. Once summer temps come around and that sleeve opens up another two and half thousandths, you'll do well to keep it running, and it will have lost a significant amount of horsepower due to loss of compression.




Found this surfing the net. we all know this, but i though it was kind of cool with the measurments and all.

well maybe it's not that intresting.
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Old 08-22-2009, 07:28 PM   #2
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oh here is another idea for breakin


Steve is the Technical Editor of RC Car Action and an administrator at rcz, and is probably the world's leading advocate of heat cycling and hot temp break in. The Cliff's notes virsion of Steves method is to get the engine hot (200 F) with a heat gun before starting it the first 15 times or so. Run it rich, but not blubbery rich, at 200 to 220 F, for 1 minute at a time. Let it cool completely with the piston at the bottom of the stroke, repeat 5 times. Then go to 2 minute intervals, then 3 minute intervals. You can be driving it during this time at up to 1/2 throttle.
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Old 08-22-2009, 07:36 PM   #3
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here is another

But that is unnecessary IMO. Most of the benefits come from getting it hot first, so just get it hot and drive it. Running it cold is the biggest mistake. Here is a quote from the OS website:


"How Do I Break In My R/C Car Engine?

The break in process of model engines, especially R/C car engines has been affected by a wide variety of myths and misconceptions. The main one is that the engine must be run at idle for several tanks' worth of fuel before the model is run. There is nothing farther from the truth! In fact, running the engine at idle for several tanks' worth of fuel will not only insure that your engine won't break in properly, but it could also reduce its overall life!

The purpose of the break-in process is to run the engine so that its moving parts will polish each other to a perfect fit. This requires that the engine be run at a variety of throttle settings so that the different parts will be affected by changing pressures and temperatures.

Typically, we start out with a moderately rich needle setting and start driving the car right away. We accelerate to a medium speed and then coast. Turn around and come back the same way. If the high-speed needle is so rich that the engine tends to hesitate a lot when throttle is applied, we'll lean it a bit to eliminate most of the hesitation.

After a few minutes of this, we start accelerating to a high speed and then coast. Turn around and come back the same way. We do this for the remainder of the first tank.

During the next two to three tanks' worth of running, we gradually lean the high-speed needle valve until the engine will run at full throttle at a setting just rich of peak RPM. One way to tell that the engine is on the rich side of peak RPM is to accelerate to full throttle and carefully listen to the engine. It should accelerate up and hold RPM, and not sag back down.

With the CV-series of engines, we'll set the high-speed needle about 2-1/4 turns open and lean from there. When fully leaned, the needle will be between 1-3/4 to 2 turns out from closed. The engine may still run with a leaner setting on the needle, but that setting may be lean enough to allow the engine to gradually overheat and quit. An overheat is a bad thing, and it will cause the piston/cylinder fit to go bad very quickly. "Thermal overload" is just another term for overheating.

If the engine is set too lean, the engine's internal parts can be damaged because they'll be starved of lubrication. Remember, the engine's lubrication is contained in the fuel, and a too-lean setting means too little fuel, which translates into too little lubrication.

Finally, O.S. states in their engine instructions that you should use a fuel that has an oil content of no less than 18% by volume. Many so-called "R/C Car" fuels contain oil in the 12%-14% range. While these may work quite well when the engine's set correctly, low-oil fuels do not leave much margin of error if the engine gets a lean run. Nitro content can be as high as 20% by volume without worry about special engine tuning or setup."

Read more from OS here:
http://www.osengines.com/faq/product-faq.html#q590



I have done engines the old cold way and the new hot way. Both run fine for a long time. But the hot break in engines still have so much compression after 1+ gallon that they are hard to start cold, just like they were new. I am now in the habit of warming my engines every time, and there is no doubt in my mind that they are going to last longer amd make more power.
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Old 08-22-2009, 07:38 PM   #4
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here is yet another





I broke in my XTM by their book without a temp gun. Now that I think about it, their instructions get the exact same response from the engine as your article states. The XTM still has compression when it's cold. Plenty of fuel through this machine and it runs great.

Now, the second engine I broke in, I drove around during break in. My major mistake (thinking I knew my stuff)was running the engine slobbering rich. I had the misnformed opinion that the extra fuel would carry away any particles and add the extra lube I needed for break in. What actually happened was the extra fuel kept the engine too cool to expand and make a nice fit. /sarcasm on: This engine lasted me a whole 1.5 gallons /sarcasm off.

SO I guess I'm here to back your claims. Running an engine so slobbering rich, or so low in the rpm band that it can't warm up to operating temp, (during break in)will significanty shorten the life of your engine.

I wish I came across this before my second break in attempt.

BTW the XTM is still extremely strong, and has seen more use.

Thanks for taking the time to share this with
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Old 08-22-2009, 08:42 PM   #5
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If you wrap the cooling head with a few wraps of
aluminum foil during the start of the break-in prosess.
You can run the engine realy rich and still maintain the
temp over 200f.. It works for me.
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Old 08-23-2009, 08:35 AM   #6
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Also when running a very rich setting for break in, u are adding stress to the motor, more fuel added in the chamber means more stress on rod and crank during breakin. in this i mean that the very rich setting has un burnt fuel causing higher compress.
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