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.
Issue link: http://experimenter.epubxp.com/i/113663
Un d e r t h e C o w l have deep stains? Is the exhaust system secure and in good shape? How does the air filter look…like it's original from 1974? Don't be satisfied with a peek down the oil-stick hole, either. Insist on enough access to look at everything. But while you have the dipstick out, don't forget to look at it. Is it perfectly clean? That's unusual. Is the end chewed up? Not good. Is there a lot of oil near the fill hole? Why? Have a look at the donor airplane's interior. Look for lots of oil containers, bags of spark plugs, huge toolboxes with every possible wrench in there, or lots of greasy rags. These could be signs of trouble! Are there broken fins on the cylinders or heads? Small chips that are ground smooth (but not to the base metal) are probably okay. No matter whether the engine is mounted and running or on a skid, you should perform compression checks on all cylinders and look into all cylinders. Put a bore scope through both spark plug holes. Removing the valve covers gives you access to the valve stems. Rotate the engine until the valve is released and wiggle the end of it. Is it loose? Are they all the same "looseness"? (An experienced mechanic knows just the right amount of "loose.") You probably can get permission to check if the pushrods are bent, and you should look. You may also get access to the tappets and cam; if so, take a good look. (On most engines, this requires pulling a jug or two. Expect to pay for that labor.) If the engine is naked, that's good and bad. You can't do a "hot" compression check or inspect the engine mounts (where sloppy maintenance is a clue to other sloppy maintenance). But you can see everything; use the opportunity. Grab all the accessories, and make sure they're mounted securely and that their fasteners are in good condition. Move the prop hub; end play is always present (check the manual for limits), but side play that you can feel isn't good. Check the magnetos. See what the points look like and check if the rest of the internals—the drives and so on—are in good shape. Spark plug wires are expensive. You want good ones. If the engine is even lightly covered with grunge, get the owner's permission to clean it. Look for anything unusual; a thick buildup may signal a leak in a seam or oil seal or even a crack. (Remember that cracks don't usually start in the middle of things; look at every edge, every hole, every fastener.) Are the fasteners properly installed with two threads showing through fiber locknuts, and are washers where they belong? Are all fasteners aircraft grade? Is the safety wire on backwards (indicating work by a nonmechanic)? What is the history of oil changes? Remember that it's not just hours that hurt; condensation and chemical deterioration occur when the engine is quiet, too. Look at the oil screens. Ask if there has been a history of oil analysis (and if there has been, check the serial numbers on the reports against the engine's number). It's well-understood in the industry that "overhaul" and "rebuild" have no definitive meanings. If your engine has had such attention, look at the parts list for a better idea of what was "overhauled." And on recent factory—and a very few independent—rebuilds of 320, 360, and 540-cubicinch Lycomings, you may have the newer roller tappets and cam. That's great, but expect to pay for the goodness. Above all, beware of bargains. If you're buying a suspect engine because it's all you can afford, consider how much it will cost if any of your suspicions—even just one of them—gets confirmed! Lycoming Tips and Specs You Can Use A quick read of the Lycoming manual on the O-320 and O-360 yielded some quick specs and tips that you can use to your advantage—from outside the engine. • • • • • Penn Yan put a window in a valve cover, to show how much moisture can accumulate, just from condensation. Frequent use (fying) is the only remedy, though frequent oil changes defnitely helps! 38 Vol.2 N o.3 / M arch 201 3 Crankshaft end play: 0.026-inch max Prop flange max runout TIR: 0.005 (new limit 0.002) Fins may be ground down, but never into the base metal. Look for evidence of improper tool use. Welds on certain parts are okay. "For example, almost any area of a rocker box may be welded, but no part of the cylinder head except the fins may be welded." (Lycoming Overhaul Manual, Section 3, Page 2, revised January 1970.) » More information is available at these websites: www.PennYanAero.com and www.Lycoming.Textron.com. Photography courtesy Penn Yan Aero