Experimenter

May 2013

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

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Un d e r t h e C o w l remove, say, gasoline that gets into the oil from overpriming. Change the filter often, ideally every time you change oil, which should be at least as frequently as the manufacturer recommends (by both hours and calendar; water accumulates even when the Hobbs meter isn't running). Don't use automotive filters on airplane engines. In 2008, I wrote that Steve Staudt of Champion Aerospace emphasized that oil serves a dual purpose: lubrication and cooling. "Since [Continentals] and Lycomings are air cooled, they flow a tremendous amount of oil through the lubrication system, hence through the filter." Oil is essential to proper cooling. For comparison, "A liquid-cooled automotive engine may only see one gallon a minute oil flow through its spin-on filter; [but] a 6-cylinder [aero] engine can see as much as 20 gallons per minute oil flow through the filter at takeoff. (Gallons, not quarts!) You begin to understand why small, downsized automotive filters don't work on aircraft." An engine's bearings are made of softer material than what they protect. Most aviation engines have replacement bearings for high-wear items such as the main and rod bearings, and the camshaft (though the Rotax 912 runs the cam directly in the case—another reason to make sure the oil system is up to snuff). These relatively thick, relatively soft bearings do more than cushion the shocks of combustion and inertia; they also allow tiny fragments of abrasives to embed themselves, keeping them from doing extensive damage. Further, they are more porous than the metals they protect and thus "hold" lubricant in place. Oil that collects at the bottom of the engine system has been through tough times. It's been squeezed, sheared, smashed, splashed, heated, aerated, and contaminated. All of which are bad. For the oil filter to do its work, it needs oil, not air. Though air tends to bubble out naturally, many systems incorporate a specific stage to de-aerate oil; the remote oil tank on dry-sump systems separates liquid and gas. The oil cooler's purpose is obvious, but it is important to make sure that air cannot accumulate here, either. Always position the outlet at the top end of the cooler. Give air bubbles a route to escape. Te large sump on this conceptual Continental O-200 collects, de-aerates, and even cools the oil. (Note that there are no cooling fns on the cylinders.) The rest of the system is equally critical. If the oil pump stops, so will your engine. If the oil pickup tube gets blocked or falls off, your pump won't get oil. Oil lines are easy to burn, damage, or crush. They're relatively inexpensive; inspect them frequently, and don't be cheap about changing suspicious ones. A note, particularly on oil coolers and lines, but especially so for other elements in the oil system, such as crankshafts: Your shop parts cleaning tank is a terrible thing to use on these components. In its sump are all sorts of evil particulates, which easily pass through the best parts-tank filters. When you need to clean your oil lines or cooler, don't use your parts tank, even if you've just changed the fluid and filter. Proper aviation shops or speed shops (that do race crankshaft work) usually have a proper cleaning regimen. If your engine somehow ruins itself, throw away the oil cooler, oil lines, and anything else that you can. Have the remaining parts cleaned by a facility that truly knows how. If any component in the oil system fails, you won't get oil. Tis is a rather catastrophic failure, the kind of thing that happens at Reno. It shouldn't happen on your engine. 30 Vol.2 N o.5 / M ay 2013 What about oil heaters? In cold climates, they allow the engine to start, but in general (and there are some exceptions) they shouldn't stay on all the time, as they're not hot enough to boil out the water, and corrosion, of course, ac-

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