High-Time or Low-Time Engine?

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When looking to purchase a used airplane, prospective owners are often confused about whether to get a plane with a ''new'' (overhauled) engine -- and pay a high purchase price -- or get one with a run-out engine and do the overhaul to a quality level they can control. Brian Jacobson analyzes both possibilities.

Odyssey Aviation Publications

There are three issues that confound many potential aircraft purchasers as they are searching for the right aircraft: airframe time, avionics equipment, and engine time. Each can have its own lasting effect on the aircraft that is purchased, leaving the new owner with the potential for higher maintenance bills as well as a higher or lower resale value.

While airframe time and the type of avionics equipment installed are not to be dismissed lightly in any purchase, each will be the subject of a future article. For now, let's look at the effects of a high- or low-time engine upon the purchase and operation of a new aircraft.

The question asked most often during the purchase process is, "Should I buy an airplane that has a recent engine or a near-run-out engine?" That one is followed quickly by, "Am I better off to have an engine that was overhauled to my specifications?" The answer, which is often the same when it comes to spending any money on general aviation airplanes, is "It depends."

High-Time Engines

There are many reasons why a purchaser would buy an airplane with a high-time engine. For example, if an engine has been used 1,700 hours out of a 2,000-hour TBO, the time remaining could serve the new owner for many years, depending on how many hours a year he or she flies. Actually, the average for most light, single-engine airplanes flown by private owners is between 50 and 100 hours per year. Many are flown less than 50 hours a year.

So, a potential buyer could purchase an airplane with 300 hours left to TBO at a value considerably lower than one with a much lower time engine and not have to worry about the engine overhaul for several years, providing the powerplant was in good condition and truly has 300 hours of life left. That could give him the time he needs to resuscitate his bank account following the purchase and provide the needed funds for the overhaul.

That strategy is a good one as long as no major airframe or engine maintenance is required during the time the owner is saving for the engine overhaul. If the compression starts to drop suddenly after 100 hours and the mechanic determines it is necessary to overhaul the engine early, then our fledgling aircraft owner has "lost a bet," so to speak. He gambled that he could get 300 hours out of the engine and lost. That could severely affect his finances under this purchase scenario.

Sometimes the person who buys an aircraft with a high-time engine and hopes to get the requisite time out of it before the overhaul is trying to buy into a make and model that he truly can't afford. He stretches his finances to the max. to make the deal happen, and then crosses all of his fingers and most of his toes in the hopes that nothing significant will happen until it's time to yank the engine. In fact, when the engine finally does make it to TBO, it is this person who may elect to continue flying the engine and put the overhaul off even further.

And when the mechanic finally tells him that it is time to overhaul the engine, this person is likely to top-overhaul the cylinders and put the airplane up for sale, largely due to the fact that he or she has not been able to save enough money for the complete overhaul. The fallacy with this approach is that a top overhaul adds no value to the aircraft. It is strictly a function of maintenance that is necessary to keep the aircraft airworthy. So, when our aircraft owner prices the airplane for sale and includes the cost of the top overhaul, the airplane won't sell because it is overpriced and in need of an engine overhaul.

Some are blessed with no major problems with their airplane and are able to save the money necessary to overhaul the engine when it is time. They do the job and have an airplane that they can continue to fly with restored confidence in the engine.

High Performance = High Costs

Buying an airplane with a high-time engine with the expectation of overhauling in the future works best on the non-turbocharged, low-performance powerplants like those found in the Cessna 172, Piper Warrior, Archer, etc. As you move further up the "engine chain" the situation changes as the engines become more complex and the chances of them making TBO are reduced, depending on a number of factors.

Most of them revolve around the care and feeding of the engine during its life, to which the new owner can contribute little. It is expected that many turbocharged engines require a top overhaul and turbocharger replacement around mid-life. Then, depending on how the engine is operated, the cylinders may or may not make it through the second half of the engine life. Another factor that will help to determine how far the top overhaul will go is whether the cylinders are field overhauled or are replaced with factory-new cylinder kits. Of course, any field overhaul of cylinders, or an entire engine, for that matter, is directly related to the quality of work performed by the person or shop.

What will it take to overhaul the engine when you get to that point? First, you have to buy the engine, whether you pay a local engine shop to overhaul your engine or go to the factory for a replacement. Then, there are other charges such as the removal and replacement, propeller overhaul (if it is due), and other maintenance items that are done at overhaul, such as replacing fluid-carrying hoses and other components. You can expect to pay about $5,000 to $6,000 per engine over and above the cost of the engine overhaul itself in these charges. Turbocharged engines may have an added cost in exhaust-system repairs or replacement. How much will that affect the value of your airplane? The only added value to the airplane is the cost of the engine itself. The rest, including the removal and replacement of the engine, are considered maintenance items and do not add value.

So, you can see why our hapless aircraft owner might choose not to overhaul his engine, but to top overhaul instead and then attempt to sell the airplane. If he overhauls the engine and then goes to sell the airplane, he will lose the $5,000 to $6,000 per engine that he spent over and above the cost of the engine itself. But, he will also lose the value of the top overhaul, if he goes that route, which could be the same amount of money or more on a light, single-engine airplane, depending on who does the work and how it is done. But he might go that route because he doesn't understand that there is no added value for the top overhaul.

A Young Engine

Now, let's look at the purchase of an aircraft with a low-time engine. Of course, the airplane will cost more because the value of the engine is higher. And that value will depend upon whether the engine is factory remanufactured, field-overhauled to new limits, or a simple field overhaul. What's the difference?

The factory remanufactured (also called "rebuilt") engine is similar to a brand-new engine in that it has no time in service. It is called a zero-time engine, just like a new one. The engine field overhauled to new limits is one where a shop has taken the engine, inspected all of the components, and installed components that meet the manufacturer's accepted limits for a brand-new engine. In fact, Lycoming offers factory-overhauled engines that are nearly as good as a remanufacture. Many more new parts are used in the assembly, including new cylinder kit assemblies. Continental does not offer factory-overhauled engines.

A field overhaul is one where a local shop or mechanic disassembles the engine, inspects it, replaces any parts that are worn beyond minimum tolerances, reassembles the engine, and reinstalls it on the airplane. This is the cheapest form of overhaul and is less likely to get through another TBO cycle without major maintenance. A small engine (150 hp or less) may work well with a field overhaul, but on larger engines care must be taken in choosing the person or shop to do the work.

When purchasing an airplane with a recent overhaul, the quality of the work is very important. Most people look for the name of the shop, and if it is one of those recognized in the industry as a "national overhaul shop," that airplane will sell faster than will one where the name of the mechanic who signs the logbook is unknown. There are some mechanics who do excellent work, but to someone from another part of the country they are not known. During the prepurchase inspection it is incumbent upon the inspecting mechanic to study the engine and the overhaul entry in the logbooks in an attempt to determine the quality of the engine overhaul.

Low-time engines can have problems as well depending on who did the work. During appraisals I have seen logbook entries that detail an overhaul followed by either major engine repairs or a second overhaul within a hundred or two hundred hours of the first. If you find an airplane with that kind of entry, make your prepurchase mechanic aware of the second overhaul and let him determine the condition of the engine.

An engine that was overhauled using new cylinder kits instead of overhauled cylinders should give its owner better service. This is very important on engines of 200 horsepower or more. It is not unusual to see multiple cylinder problems in logbooks of engines that had original cylinders overhauled. Repairing or replacing cylinders periodically can be expensive during the life of an engine.

Typically, if an engine was overhauled properly and has flown 150 to 200 hours with no problems, its chances of reaching TBO are better than one that has had major problems early. And, like the owner who bought the high-time engine, you are just as interested in making it to TBO.

Many aircraft owners who buy airplanes with low-time engines don't put money away for overhaul, because they figure they will only own the airplane for a few years, sell it, and step up. But that is not always a good plan. Figure out what the engine overhaul will cost and put away money based on an hourly cost to overhaul it; if you have an incident where major engine work has to be done, at least you will have some money put away for repairs. That will help alleviate the financial burden of making repairs should something unexpected happen. If that does not happen and you do sell the airplane in a few years, you can use the money you set aside for the new purchase. If, for some reason, you decide not to sell and hang on to the airplane, then you will have money set aside for an engine overhaul whenever you reach that mark.

Buying an airplane is hard work. Make sure you do all of your homework regarding your finances before you start looking at airplanes that are for sale. Part of that homework is to know how much money you have to spend, how much airplane that will buy, and if the make and model you have selected is the best for your needs, whether that equates to a low-time or high-time engine.

More articles about buying aircraft are found in AVweb's Used Aircraft section..