jaymen
Posts: 432
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Joined: 3/26/2003
Last Login: 5/7/2013
From: Mission Viejo, CA, USA
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Well, I used to work at Cox and here is what we did:
The time to re-set the piston/con rod is when the engine is new, BEFORE the crimped socket work hardens from running, so check it and do it now if it is loose.
Depending on the vintage and quality of the TDs you have, some of the older ones had a a very tight fitment of the piston and cylinder due to the tapers, while laters ones have a relatively sloppy fit and little or no taper. This then means that the tight ones will take over an hour or more of break in while the sloppy ones will be ready after as little as 5 minutes of running. If the piston gets real tight for the last 1/16 to 1/8 inch of travel, at the top of the stroke (glow head removed) it will need a longer break-in. In any case, here is how we broke them in at Cox prior to testing them for peak RPM:
Run the TD .049 on 15% fuel and use a smaller prop, like a 5x3. Keep the glow plug clip on and run it sloppy rich for the first couple tanks full ( about 5 minutes each time) and let it cool between runs. Check that the glow head is tight after it cools. You will notice some greyish-black metal in the oil during the first run, but it shoul go away by the second run. The idea is to keep the engine turning fast but rich, with a smaller prop.
Run several more tanks with the glow clip removed, you will have to slightly lean the needle valve to keep the engine running, but keep it on the rich side. Next, after cool down and torqing the glow head, run it a bit leaner such that it is on the verge of occasionally 2-cycling. The engine should be 4-cycling, but going back and forth between a 2-cycle and 4-cycle. This will begin to build a little heat in the engine. Repeat this 3-4 times for 5 minutes each and then with the engine running, pinch the fuel line to momentarily lean out the engine for full rpm for about 5 seconds, then release the fuel line and let it go rich for about 15 seconds, then repeat. If at anytime during this process the engine begins to sag while you are pinching the line, it's getting tight and is not ready for full RPM, or you just pinched the line too long and it's running out of fuel. If all is well, try leaning the needle valve a little more until it the engine is just barely missing a little and almost on a clean 2-cycle. It should be making a "whee....da-deee......da-deee..." sound. If the engine can hold this setting without sagging, try pinching the line again and see how it runs when lean. Run several more tanks and then try leaning it fully. If it sags, open the needle valve and continue the break in with it set so it just misses as described above.
Once the engine will hold a lean setting without sagging, you are ready to try the full size prop. Bolt on a 6x3 grey and start over with a rich run where its on the verge of breaking into a clean 2-cycle as described above. Pinch the line and note how it holds the lean setting. If it seems fine, try leaning out the needle valve fully on the next run. Loose engines will be ready at this point, but tight engines will require more rich running with a full load( the bigger prop) before they can hold a lean setting. Since no two are alike, you have listen to the engine to determine when it is ready. If the engine will not hold a lean setting and tightens up, go back to the 5x3 and continue break-in at a fast 4-cycle for another 15 minutes. On tighter engines, it is well worth the extra effort, as they will be real power houses once broke in, but if you rush it you will ruin them.
Many times, if the engine is tightening up repeatedly, it may have varnish/shellac in the cylinder and you will have to scour the cylinder wall with #0000 steel wool or a devarnishing brush ( rifle bore brushes work well). Clean the cylinder, lube, and re-assemble the engine and continue the break-in.
Do the same for the .09 TD. The secrets are using a small break-in prop to allow the engine to build RPM, while running rich to avoid a heat seizure, allowing the engine to fully cool between runs (heat cycling) and slowly bringing up the RPM incrementally as the break-in progresses. An extended break-in will not hurt an engine, but you can ruin a tight engine by not breaking it in long enough.
Have fun, good luck!
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All Forums >> RC Airplanes >> "1/2 A" & "1/8 A" airplanes >> Advice for first running of a .049 and .090 
Advice for first running of a .049 and .090 - 
