Airframe and Powerplant

Major Decisions

November 1, 1992

An overhaul primer: The whys and wherefores of the "major."

Unless you fly a Cessna 172 with electronic flight instruments or a Piper Cherokee with solid-gold yokes, it's likely that the engine is the single most expensive piece of gear on the airplane. Over the airplane's lifetime, the engine will probably require the lion's share of the maintenance budget. What's more, it is the one component on a light airplane with a conspicuous known (or estimated) lifespan. Expressed in hours but also measured by the calendar, this time between overhauls (TBO) is a recommendation cloaked in controversy.

Engine manufacturers base TBO numbers on field experience as well as testing done during research, development, and certification of the engine or engine family. These figures often start out small and grow as the fleet accumulates hours and weak areas are identified. Whether your engine makes it to TBO depends upon a complex set of variables that includes pilot skill, ongoing maintenance, installation effects, and, perhaps most important, frequent use.

It doesn't matter if your powerplant's TBO is 1,200 hours or 2,400, sooner or later, you'll have to overhaul it. Many owners question when an engine should be overhauled. If you operate under Federal Aviation Regulation Part 91, you are under no obligation to tear the engine apart at the maker's TBO. (FAR Part 121 and 135 operators are required to overhaul at TBO unless a TBO extension is obtained, which is quite common.) Most engine gurus recommend watching the engine closely from day one, taking lubricant samples at each oil change for spectrographic analysis, keeping track of oil consumption, and cutting open the oil filter at each change to look for impending doom in the form of metal particles. Also, keep an eye on compression tests and overall performance during the engine's life; this way, you have established a baseline against which you may more readily see anomalies. If the engine is running well, using its typical amount of oil, there are no unusual readings on the oil analyses, and the compression is good, by all means keep running it. You should be more vigilant as the hours on the tachometer roll up past TBO. And keep an eye on those accessories like magnetos, vacuum pump, fuel pump, and turbocharger; in many cases, their life is shorter than the engine core's.

There comes a time, though, when the signs point to an overhaul, and then one pulls back the cover on a whole book of questions. Which is better, factory or field overhaul? Should I overhaul to service or new limits? Who should do the work, my local FBO or an engine shop? And what about factory-new or remanufactured engines — are they worth the cost?

The FARs on an overhaul call for the engine to be disassembled and inspected. All parts not conforming to the service limits prescribed by the powerplant manufacturer must be overhauled or replaced. Certain parts must be replaced if they are part of an airworthiness directive. (Some shops consider parts specified under a mandatory service bulletin to be mandatory replacements, although this practice is not required by law.) In theory, you could have an engine at TBO torn apart to find all tolerances within service limits and then have it reassembled with little more than new gaskets and a fresh coat of paint. And you'll have a freshly overhauled engine with all the same pieces that have been hammering about for the last 2,000 hours still in place.

Sure, this is legal, but is it good practice? Not really. Because you run the risk of having one of those components wear beyond the service limits sometime after overhaul but before the next TBO, this amounts to little more than a paper overhaul — for practical purposes, you would have been better off just leaving the engine in service. That these paper overhauls take place ought to make you suspicious of an airplane for sale with a newly overhauled engine. Generally, it's a better deal to buy an airplane with a run-out engine and oversee the rebuild yourself; that way, you know what you're getting, and you have some control over the critical break-in period.

If you intend to keep the airplane awhile, the new-limits overhaul is the obvious and prudent way to go; but where should you have this done? Today, there are several sources for engine overhauls, from your local A&P to one of the large overhaul shops to the original engine manufacturer. Prices vary all over the board, with the small shops and independent operators often the least expensive, thanks to low overhead. But you must be cautious and ascertain exactly which parts will be replaced and which limits will be used. Also, the engine you own will help dictate the shop: It's almost surely false economy to take that complicated GTSIO-520 to Joe's Aircraft for the major. On the other hand, Joe may have cranked out many an O-320 overhaul in his career, and his handiwork could well be as good as the factory's. Similarly, you should carefully seek an overhaul facility that is familiar with your brand engine, because while in the grand scheme Continentals are a lot like Lycomings, there are enough detail differences that a shop familiar with one won't necessarily be so handy with the other.

Of the factory overhauls themselves, there are several types. When you call up Williamsport or Mobile, the people at Lycoming or Continental will be ready to sell you on either a factory-new, remanufactured, or overhauled engine. New is new — everything fresh off the assembly line and a clean logbook to boot; but thanks to low production rates and high labor costs, a new engine's price can be truly eye-watering.

The next best thing to factory new is a factory-remanufactured, or zero-timed, engine. Used engines come into the factory and are disassembled and inspected. If the core passes muster — in other words, if the crank, case, camshaft, and other lower end components are in good shape — new cylinders and accessories are attached. Because the factory has essentially put the engine through the same assembly and quality-assurance steps of a new engine — only some used components — the Federal Aviation Administration allows it to assign a new logbook and a revised serial number. In the eyes of the Feds, the result is a new engine. (This process, by the way, provides the factories with tremendous feedback as to the health of the engines in the field, and many running changes are prompted by what the engineers find in used powerplants.)

Finally, there's the factory overhauled option, which mates a used engine with many new components. In Continentals, you get new pistons, pins, valves, and springs but overhauled cylinders. With the Lycoming alternative, the entire top end is new-manufacture, while the bottom-end components are brought up to new-limits standards. Be aware that there are some high-time jugs out there, especially for engines in trainers or high- utilization commercial aircraft. Without knowing it, you could have a first-run bottom end mated to 6,000-hour cylinders.

While it might seem ideal to have the factories do all the work — they should know the engines, after all — there are a few items to consider. When you opt for a factory overhauled or remanufactured engine, you are giving up old faithful. Your old engine goes into the pool, and you get someone else's. Which can mean one of two things, depending upon the "experience" of your engine: a first-run, oil-tight wonder or worn-out maintenance hog.

But if you have a recent-vintage airplane working on the first overhaul, you might want to consider keeping it around. Right or wrong, many mechanics and pilots believe there are good and bad engines, even among the same types, and if you've had a good ride, you ought not to switch horses midstream. Another issue: If your engine has been superseded or heavily altered by the factory, you might pay a premium to get the upgrade. An example: The Continental TSIO-360 has been updated several times since some of the host airplanes have been built, and if you have, say, an F-suffix engine, be ready to shell out extra for the -FB engine; Continental doesn't overhaul the straight F engine anymore. Some of these changes are relatively minor, like different piston designs to help control oil consumption, but others are major, like beefed-up crankshafts, larger main bearings, and heftier connecting rods. It's worth a call to the factory to see what has been changed along the line. What's more, if you are the proud owner of an unusual or very old engine, the factory route might not even be available to you. Lycoming isn't too thrilled to see an IGSO-480 come through the doors these days.

Other questions that usually arise at overhaul time: Should I go for steel or chromed cylinders, or one of the newfangled Cermicrome processes? Utilization is the key here: For a 400-hour-a-year airplane, straight steel barrels are usually preferred, thanks to their better heat distribution and quick break-in. But if yours is a seldom-flown airplane, going chrome or Cermicrome could cut down the cylinder corrosion and extend the calendar life of the engine. Check with the overhauler (or several of them) to see what they recommend for your particular engine — some powerplants do better than others with chromed cylinders. There are also several recent options from the folks that brought you Cermicrome, Engine Components, Incorporated, like stress-relieved heads mated to new steel barrels, and a ceramic-impregnation process for basic steel cylinder sleeves.

For basic comparison, you should compare the factory to field overhaulers along the following lines. Exactly which parts are replaced? Are the accessories — magnetos, starter, alternator/generator, turbocharger and controller, propeller governor — overhauled or replaced? Does the engine get new cylinders, the old ones overhauled, or something from an open pool of jugs? Who pays for cracks found in cases or cylinders: Many overhaul costs are predicated upon the parts in your engine being "serviceable." Also, you must be cognizant of the amount of power your engine produces and how it's used: A 150-horsepower engine in a simple four-place airplane will require a different level of service than that 380-hp, turbocharged monster in your Duke.

As truisms go, the idea that you "get what you pay for" is often heard — but it is an all too accurate description for the major overhaul. Shop around, get a competitive rate, but remember that a high-quality overhaul you usually buy just once; a cheap one, you might pay for again and again.

What It Costs

We've discussed the different types of major overhauls, but nothing brings out the differences like good old greenbacks. Not surprisingly, the range of overhaul prices is tremendous and depends greatly upon the source and type of overhaul.

To get a feel for the costs, we acquired quotes for an overhaul on a 285-hp Continental IO-520-B engine, found in many iterations of the Beech Bonanza. This is a popular engine, with the basic core and cylinders used in many models within and without the Beech line. The span of prices ought to apply well to most popular engine types; those airplanes with unusual powerplant types will probably see a greater variation. The more uncommon the engine, the more it becomes a seller's market.

Starting with the factory's work, you can have a remanufactured IO-520-B for $18,692 exchange or $26,692 outright. A brand-new IO-520-BB (which is a heavy-case, large-crank version of the -BA, which is no longer in production) will run $34,528 with an exchange or — are you sitting down? — $42,528 outright.

Mid-States Aircraft, a large overhaul firm based in Tulsa, quoted us several prices for the IO-520, starting at a base price of $12,700 for a new-limits overhaul with Cermicrome cylinders. (The company doesn't do service-limits overhauls.) From there, you can add ECI's refurbished cylinders (which have been stress relieved and mated to new sleeves) in the Cermicrome process for an additional $600, or with the Cermisteel process for an extra $1,350. Also, you can opt for factory-new steel cylinders for $4,200 above the basic overhaul.

Small, local shops are harder to pin down on price because they replace parts on an as-needed basis, and the mechanic often doesn't know what's repairable until the engine's all over the shop. One shop did say that the last IO-520 that came through cost the owner about $14,000 for a new-limits overhaul.

When you go shopping for an overhaul, you should consider some other factors in your budget. Labor for removal and replacement of the engine and shipping can add substantially to the cost. Here again, it pays to go with shops or mechanics familiar with your type of airplane, and you could save a fair chunk of cash by using an overhaul facility near your home base. Also, unless your propeller has recently been overhauled, it makes sense to do so while the engine's apart. Other considerations include replacement of hoses and engine mounts, as well as cowling hardware and baffles. Having the engine majored is just part of the equation. — MEC