Aircraft Maintenance: Know your engine overhaul options
Few maintenance decisions are as consequential as what to do when it’s time to overhaul your engine. To make the best decision possible, you need to understand your options.
Aircraft owners can find themselves contemplating overhaul or replacement of an engine for several reasons, including severe mechanical issues, reliability concerns, or simply age and hours in service. Although engine manufacturers’ time between overhaul recommendations are not mandatory for FAR Part 91 operators, lower-time engines support the value of the aircraft, insurability, and peace of mind. Of those factors, the impact of value and insurability often go overlooked. For example, a friend of mine had her engine damaged by a maintenance facility when it was accidentally run without oil. The shop admitted guilt, but their insurance refused to pay because the engine was past TBO. Their argument was that the value of the engine was limited to a core value (which was still intact) because of the excessive hours.
Factory-new engines
A factory-new engine is exactly that: Every part of the engine and its components are brand-new, produced to factory-new limits. This can be especially important as it relates to different materials involved. Steel, for example, has an infinite fatigue life when operated at stress levels below its fatigue limit. For parts such as crankshafts and connecting rods, we only have to worry about wear limits because they will never fail due to fatigue when operated within normal limits. Aluminum, on the other hand, has a finite fatigue life and will eventually fail even from low-stress cycles. Aircraft manufacturers consider this when designing aluminum parts and it is rarely a concern. However, I know of several owners who prefer new engines simply because of the fact that every part, including the aluminum engine cases, is guaranteed to be made of brand-new metal.
Tolerances are another key factor to consider. Manufacturers have two sets of limits: new part limits and serviceable limits. Choosing a factory-new engine ensures that every part meets new part limits. The same factors apply to every engine component, from the fuel system, magnetos, starter and adapter, and alternator and drive coupling. Every part, from the housings to the smallest screw, is brand-new and meets new limits.
Lastly, new engines come with a new logbook, no previous history to be concerned with, and generally longer warranties from the factory.
Factory-rebuilt engines
A factory-rebuilt engine offers nearly all of the benefits of a factory-new engine except for the new metal. A rebuilt engine as defined in 14 CFR § 91.421, “is a used engine that has been completely disassembled, inspected, repaired as necessary, reassembled, tested, and approved in the same manner and to the same tolerances and limits as a new engine with either new or used parts.” This means that you are getting all the same wear limits you would get from a new engine, but the factory has the option to meet those requirements using reconditioned parts.
I spoke with the team at Continental Aerospace Technologies to understand the company’s approach to factory-rebuilt engines and was surprised to learn how few used parts actually go into a Continental factory-rebuilt engine in practice. Continental’s extremely high standards for the reuse of parts means that new parts are often substituted when a suitable used part is not available. For example, depending on the availability of used cases that meet its strict standards (no machining or repairs allowed), Continental may use a brand-new case in a rebuilt engine. They also use brand-new cylinders, which come with a 24-month warranty. Similar to a factory-new engine, a rebuilt engine leaves the factory with a brand-new, zero-time logbook. This means that for many owners the difference between a factory-new and factory-rebuilt engine might come down to just the difference in the total engine warranty (24 months for new, 18 months for rebuilt).
Overhauled engines
An engine overhaul (also known as a major overhaul) consists of disassembly, inspection, repair, reassembly, testing, and return to service of the engine. Overhauls may use either new or serviceable limits. Therefore, it pays to be an educated consumer and get into the details about what you are getting from whomever is doing the work. There are many different overhaul facilities and they all offer varying levels of overhauls, from simply meeting the basic definition of an overhaul in the manufacturer’s overhaul manual, to custom overhauls with many brand-new parts. Even Continental sees the market need for overhauled versus new or rebuilt engines. The Continental Services division is a complete maintenance, repair, and overhaul facility located in Fairhope, Alabama, that performs engine overhauls to new limits, offering owners options other facilities simply can’t. For example, customers can send an engine in for teardown and inspection, preserving their options for overhaul, rebuilt, or new engine choices until they see the teardown report. If serious issues are found in the engine, a new or rebuilt engine may actually be less expensive than an overhaul. In addition, Continental Services’ new-limits overhauls include new Continental cylinders, new camshaft and lifters as well as new Bendix magnetos, harness and spark plugs, starter, starter adapter, oil cooler, and fuel system.
Making a decision
There are many factors to consider when it’s time to overhaul or replace your engine. Timing is key for many pilots because factory-new or rebuilt engines can be done on an exchange basis, allowing the engine swap to be done as one task, rather than waiting months for your existing engine to be overhauled. Another benefit of the engine exchange path is that you can choose to exchange your engine for a more powerful engine via supplemental type certificate. Upgrading from a 285-horsepower Continental IO-520 engine to a 300-horsepower IO-550 is a common modification that many owners take advantage of.
I recommend that you start at the top and work down, comparing your options along the way. Begin by pricing out new and rebuilt engines from the factory, researching lead times, warranties, and upgrade options. Then compare those as the “gold standard” with the various overhaul options you find. Ask lots of questions and compare the cost-saving options against the compromises you may be making. Every situation is unique and details matter. However, the time you spend up front will pay dividends for decades to come, flying behind your new engine. Until next time, I hope you and your families remain safe and healthy, and I wish you blue skies.
