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A 160-hp O-320-D engine.
Cream Puff vs. Wrung Out Shopping for a used O-320/360 BY TIM KERN
SOME OF THE MOST popular four-cylinder aviation engines are the Lycomings with nominal displacements of 320 or 360 cubic inches. Other engine manufacturers have adopted these basic designs (with small and sometimes large changes), but this article will focus on the original engines produced by Lycoming. The used market has plenty of both good and bad examples available. When shopping for a used engine, the first piece of advice that experts offer is this: If something sounds too good to be true, it probably is. Bargains often aren’t bargains. Unless you have personal experience with the engine or know the seller well, be suspicious of any great deal.
Corrosion on the outside often indicates corrosion on the inside, but a clean exterior doesn’t always mean the inside is good. The second important step to take is to examine (and verify!) the paperwork. No logs—no sale. Check the serial numbers of the accessories; sometimes older parts find their way onto an engine that’s about to be sold. Make sure airworthiness directives (ADs) have been complied with, but it is not mandatory that every service bulletin (SB) be followed. It’s good to where an owner left off incorporating them. Likewise, verify any supplemental type certificate changes that may
90 Sport Aviation June 2010
have been installed. (Lycoming has been converting engines to use roller tappets for several years now, any time it performs an engine overhaul. Many private shops, too. If the engine has had recent major service, check. Roller tappets are good.) Ensure that your engine is truly complete. A couple little parts that are missing may be expensive or impossible to find. Get a good idea of the engine’s recent life. Has it been in an airplane, running, or is it dirty, under a workbench, or sitting in a puddle of oil? When was it last run? Serviced? How was it put up for storage and when? What recent service was performed, and who did it? Can you verify that the claimed work was performed? Were there any squawks, and have they been resolved? How, and by whom? As a general rule, the longer an engine has sat idle, the closer you should look at it, including long periods of idleness years ago. But recent inactivity is potentially the most damaging. Recent periods (since the last annual) of as few as three months can be significant, depending on the storage conditions.
PHOTOGRAPHY BY TIM KERN
WHERE TO FIND AN ENGINE Lycoming (www.Lycoming.Textron.com), Penn Yan Aero (www.PennYanAero. com), Teledyne Mattituck Services (www. Mattituck.com), Barnstormers.com or any reputable rebuilder (and there are dozens!) sometimes have overhauled or remanufactured engines available, though typically they are set up to rebuild yours through a core exchange. They’ve already gone through these engines and fixed everything you’d find in this article. You should also expect an upgrade to Lycoming’s roller tappets at rebuild time, or in any rebuilt engine. To find a used engine, check issues of Trade-A-Plane, your airport’s bulletin board, the classifieds of your favorite aviation magazine, or even Craigslist and eBay. And, ask around; it’s likely a friend, your airframe kit manufacturer, or the local airport bum can give you a line on a used engine.
the oil. A drop of oil from the dipstick on a white paper napkin can leave telltale metallic residue. While that test is not definitive, it can help you spot possible wear; it also may help you get a better deal. (Does the dipstick look like it has just been cleaned with lacquer thinner? A shiny dipstick makes a good impression, and cleaning it is quick and easy. Perhaps the engine is pristine; perhaps only the dipstick is.) Go flying, listen, and note the numbers. They will not only help detect possible trouble, but also give a rough baseline for what you
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If the engine has been overhauled, what does that mean? Who did it? What parts were used? New or old parts—or both? Get the service ticket and compare available serial numbers to those on the engine. Reputable shops have good reputations for a good reason. An individual may be a gifted craftsman, or not. If you don’t know, you can investigate—or get a lower price. (If the seller immediately offers a lower price rather than information, it may be prudent to be suspicious.) Is the engine still complying with its certification or has it devolved into experimental status? There may be nothing wrong with an experimental engine, but it will be less pricey and will forever remain so. Remember, too, that certified engines are run within certified limitations. (An experimental engine may routinely have been run too hot, for example.)
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The fun starts when you physically examine the engine. Corrosion on the outside often indicates corrosion on the inside, but a clean exterior doesn’t always mean the inside is good. If the engine is installed and is in running condition, start with a preflight. Check for leaks; look at
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might expect in your upcoming installation. Numbers will change in urgency as your test program develops, but give immediate attention to oil pressure and temperature, as well as cylinder head temperatures. Note any large or unexplained discrepancies, from cylinder to cylinder. Exhaust gas temps may vary, as probes are often occupying unusual or non-standard locations; learn what’s normal for the installation. If possible, perform a leak-down test. (The absolute numbers are generally less important than the differences among the cylinder readings themselves, unless, say, they’re all near zero.) Did the spark
92 Sport Aviation June 2010
Left: Typical but excessive wear on lifter and cam lobe. These parts are already unusable, but might be resurfaced. Right: Used but okay.
plugs come out easily? Have the threads been repaired? If so, was the repair noted in the logbook? Run a borescope into each cylinder. Look for obvious damage, traces of rust, or any differences between the cylinders’
PHOTOGRAPHY BY TIM KERN
If you can get into the engine, pull at least one cylinder. You can, on many models, inspect cam lobes;
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you can see the general condition of pistons, rings, and cylinder walls (look closely for cracks). conditions. Check all around and both toward the case and toward the head. If you can get into the engine, pull at least one cylinder. You can, on many models, inspect cam lobes; you can see the general condition of pistons, rings, and cylinder walls (look closely for cracks). Lightly chipped or ground-down fins are generally okay, but repairs should not have gotten into the base metal. Welding is a red flag and could mean a red tag (classification: junk, as opposed to a yellow tag: repairable). Check the repair thoroughly: who did it, when, and why?
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EAA 11-2009.indd 1
Take out the valves; check for straightness, wobble, deposits; look at the guides. (Lycoming’s mandatory SB-388C has more detail.) Pushrods: straight? Check the carburetor for fuel stains, loose shafts, and bent linkage. Is the starter motor shaft loose? Does the Bendix drive feel smooth? Are accessory drive gears smooth? Does the alternator turn quietly?
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Don’t assume modifications are okay. You can’t put higher-compression pistons into a low-compression engine and automatically have a high-compression engine. Model numbers matter (and there are more than 90 for each size engine, representing varying degrees of compatibility), and many parts swaps just won’t work! Even close relatives have differences. The O-360-A1A, according to www. SacSkyranch.com/Lycoming.htm, “has a bottom mounted updraft carburetor, parallel valves, 8.5:1 compression ratio, and produces 180-hp.” Yet, “the IO-360-A1A features a horizontal front mounted fuel injector, angle valves, 8.7:1 compression ratio, and is rated at 200-hp.” Continuing, the site notes the IO also incorporates non-O items: piston-cooling nozzles, a stronger crankshaft, tongue-and-groove connecting rods with stretch bolts, a tuned intake system, and rotator-type intake valves. How much power do you really need? The 360-inch engines make as much as 60 more horsepower than some 320s, and they weigh 20 to 40 pounds more, depending on model and induction. Though some O-320s are quite popular (like the 160-hp O-320-A2HD from the mid/late 1970s Cessna 172s), old “narrow deck” O-320s
Roller tappets (as now installed in all new and factoryrebuilt Lycomings) are also offered by most rebuild shops and aftermarket manufacturers. Superior’s is shown; they are all essentially identical.
are becoming orphaned, as their parts supplies dry up. (Narrow-deck O-320 serial numbers do not have an “A” at the end.) Within the 320 family, consider that prices are much lower for the 140-hp and even 150-hp models than for the 160-hp models. Experts generally agree that you won’t ultimately save money by buying a “rebuildable core,” circa $4,000. Critical parts (e.g., cranks, cases) may not be serviceable, and you may not know that. Reputable sellers (especially established dealers and parts houses) should offer some assurance of condition. It’s perfectly acceptable to demand confirmation of at least repairable (if not serviceable) major components. Private sellers, if they know their own engines, can usually offer a similar assurance. Money talks, but don’t expect something for nothing. If you’re buying a “parts” engine, you shouldn’t be paying enough to expect any warranty. Oh, and assume nothing. For instance, did you check to make sure that the engine you’re buying is a model that turns in the right direction? Your opportunities for a good buy are essentially unlimited, and it’s not that you shouldn’t buy any particular engine; it’s just that each engine, whatever its condition or history, has its own value: You shouldn’t pay too much. And if you think you’re paying too little, you should know why. Tim Kern, EAA 852075, is a private pilot and certified aviation manager as well as an aviation writer and consultant based near Indianapolis. You can find him online at www.TimKern.com.
PHOTOGRAPHY BY TIM KERN
