How Do Piston Aircraft Engines Fail?

April 9th, 2014 by Mike Busch

Last month, I tried to make the case that piston aircraft engines should be overhauled strictly on-condition, not at some fixed TBO. If we’re going to do that, we need to understand how these engines fail and how we can protect ourselves against such failures. The RCM way of doing that is called Failure Modes and Effects Analysis (FMEA), and involves examining each critical component of these engines and looking at how they fail, what consequences those failures have, and what practical and cost-efficient maintenance actions we can take to prevent or mitigate those failures. Here’s my quick back-of-the-envelope attempt at doing that…

Crankshaft

CrankshaftsThere’s no more serious failure mode than crankshaft failure. If it fails, the engine quits.

Yet crankshafts are rarely replaced at overhaul. Lycoming did a study that showed their crankshafts often remain in service for more than 14,000 hours (that’s 7+ TBOs) and 50 years. Continental hasn’t published any data on this, but their crankshafts probably have similar longevity.

Crankshafts fail in three ways: (1) infant-mortality failures due to improper materials or manufacture; (2) failures following unreported prop strikes; and (3) failures secondary to oil starvation and/or bearing failure.

Over the past 15 years, we’ve seen a rash of infant-mortality failures of crankshafts. Both Cnntinental and Lycoming have had major recalls of crankshafts that were either forged from bad steel or were damaged during manufacture. These failures invariably occurred within the first 200 hours after the new crankshaft entered service. If the crankshaft survived its first 200 hours, we can be confident that it was manufactured correctly and should perform reliably for numerous TBOs.

Unreported prop strikes seem to be getting rare because owners and mechanics are becoming smarter about the high risk of operating an engine after a prop strike. There’s now an AD mandating a post-prop-strike engine teardown for Lycoming engines, and a strongly worded service bulletin for Continental engines. Insurance will always pay for the teardown and any necessary repairs, so it’s a no-brainer.

That leaves failures due to oil starvation and/or bearing failure. I’ll address that shortly.

Crankcase halvesCrankcase

Crankcases are also rarely replaced at major overhaul. They are typically repaired as necessary, align-bored to restore critical fits and limits, and often provide reliable service for many TBOs. If the case remains in service long enough, it will eventually crack. The good news is that case cracks propagate slowly enough that a detailed visual inspection once a year is sufficient to detect such cracks before they pose a threat to safety. Engine failures caused by case cracks are extremely rare—so rare that I don’t think I ever remember hearing or reading about one.

Lycoming cam and lifterCamshaft and Lifters

The cam/lifter interface endures more pressure and friction than any other moving parts n the engine. The cam lobes and lifter faces must be hard and smooth in order to function and survive. Even tiny corrosion pits (caused by disuse or acid buildup in the oil) can lead to rapid destruction (spalling) of the surfaces and dictate the need for a premature engine teardown. Cam and lifter spalling is the number one reason that engines fail to make TBO, and it’s becoming an epidemic in the owner-flown fleet where aircraft tend to fly irregularly and sit unflown for weeks at a time.

The good news is that cam and lifter problems almost never cause catastrophic engine failures. Even with a badly spalled cam lobe (like the one pictured at right), the engine continues to run and make good power. Typically, a problem like this is discovered at a routine oil change when the oil filter is cut open and found to contain a substantial quantity of ferrous metal, or else a cylinder is removed for some reason and the worn cam lobe can be inspected visually.

If the engine is flown regularly, the cam and lifters can remain in pristine condition for thousands of hours. At overhaul, the cam and lifters are often replaced with new ones, although a reground cam and reground lifters are sometimes used and can be just as reliable.

Gears

The engine has lots of gears: crankshaft and camshaft gears, oil pump gears, accessory drive gears for fuel pump, magnetos, prop governor, and sometimes alternator. These gears are made of case-hardened steel and typically have a very long useful life. They are not usually replaced at overhaul unless obvious damage is found. Engine gears rarely cause catastrophic engine failures.

Oil Pump

Failure of the oil pump is rarely responsible for catastrophic engine failures. If oil pressure is lost, the engine will seize quickly. But the oil pump is dead-simple, consisting of two steel gears inside a close-tolerance aluminum housing, and usually operates trouble free. The pump housing can get scored if a chunk of metal passes through the oil pump—although the oil pickup tube has a suction screen to make sure that doesn’t happen—but even if the pump housing is damaged, the pump normally has ample output to maintain adequate oil pressure in flight, and the problem is mainly noticeable during idle and taxi. If the pump output seems deficient at idle, the oil pump housing can be removed and replaced without tearing down the engine.

spun main bearingBearings

Bearing failure is responsible for a significant number of catastrophic engine failures. Under normal circumstances, bearings have a long useful life. They are always replaced at major overhaul, but it’s not unusual for bearings removed at overhaul to be in pristine condition with little detectable wear.

Bearings fail prematurely for three reasons: (1) they become contaminated with metal from some other failure; (2) they become oil-starved when oil pressure is lost; or (3) main bearings become oil-starved because they shift in their crankcase supports to the point where their oil supply holes become misaligned (as with the “spun bearing” pictured at right).

Contamination failures can generally be prevented by using a full-flow oil filter and inspecting the filter for metal at every oil change. So long as the filter is changed before its filtering capacity is exceeded, metal particles will be caught by the filter and won’t get into the engine’s oil galleries and contaminate the bearings. If a significant quantity of metal is found in the filter, the aircraft should be grounded until the source of the metal is found and corrected.

Oil-starvation failures are fairly rare. Pilots tend to be well-trained to respond to decreasing oil pressure by reducing power and landing at the first opportunity. Bearings will continue to function properly at partial power even with fairly low oil pressure.

Spun bearings are usually infant-mortality failures that occur either shortly after an engine is overhauled (due to an assembly error) or shortly after cylinder replacement (due to lack of preload on the through bolts). Failures occasionally occur after a long period of crankcase fretting, but such fretting is usually detectable through oil filter inspection and oil analysis).They can also occur after extreme unpreheated cold starts, but that is quite rare.

Thrown Connecting RodConnecting Rods

Connecting rod failure is responsible for a significant number of catastrophic engine failures. When a rod fails in flight, it often punches a hole in the crankcase (“thrown rod”) and causes loss of engine oil and subsequent oil starvation. Rod failure have also been known to cause camshaft breakage. The result is invariably a rapid and often total loss of engine power.

Connecting rods usually have a long useful life and are not normally replaced at overhaul. (Rod bearings, like all bearings, are always replaced at overhaul.) Many rod failures are infant-mortality failures caused by improper tightening of the rod cap bolts during engine assembly. Rod failures can also be caused by the failure of the rod bearings, often due to oil starvation. Such failures are usually random failures unrelated to time since overhaul.

Pistons and Rings

Piston and ring failures usually cause only partial power loss, but in rare cases can cause complete power loss. Piston and ring failures are of two types: (1) infant-mortality failures due to improper manufacturer or assembly; and (2) heat-distress failures caused by pre-ignition or destructive detonation events. Heat-distress failures can be caused by contaminated fuel (e.g., 100LL laced with Jet A), or by improper engine operation. They are generally unrelated to hours or years since overhaul. A digital engine monitor can alert the pilot to pre-ignition or destructive detonation events in time for the pilot to take corrective action before heat-distress damage is done.

Head SeparationCylinders

Cylinder failures usually cause only partial power loss, but occasionaly can cause complete power loss. A cylinder consists of a forged steel barrel mated to an aluminum alloy head casting. Cylinder barrels typically wear slowly, and excessive wear is detected at annual inspection by means of compression tests and borescope inspections. Cylinder heads can suffer fatigue failures, and occasionally the head can separate from the barrel. As dramatic as it sounds, a head separation causes only a partial loss of power; a six-cylinder engine with a head-to-barrel separation can still make better than 80% power. Cylinder failures can be infant-mortality failures (due to improper manufacture) or age-related failures (especially if the cylinder head remains in service for more than two or three TBOs). Nowadays, most major overhauls include new cylinders, so age-related cylinder failures have become quite rare.

Broken Exhaust ValveValves and Valve Guides

It is quite common for exhaust valves and valve guides to develop problems well short of TBO. Actual valve failures are becoming much less common nowadays because incipient problems can usually be detected by means of borescope inspections and digital engine monitor surveillance. Even if a valve fails completely, the result is usually only partial power loss and an on-airport emergency landing.

Rocker Arms and Pushrods

Rocker arms and pushrods (which operate the valves) typically have a long useful life and are not normally replaced at overhaul. (Rocker bushings, like all bearings, are always replaced at overhaul.) Rocker arm failure is quite rare. Pushrod failures are caused by stuck valves, and can almost always be avoided through regular borescope inspections. Even when they happen, such failures usually result in only partial power loss.

Failed Mag Distributor GearsMagnetos and Other Ignition Components

Magneto failure is uncomfortably commonplace. Mags are full of plastic components that are less than robust; plastic is used because it’s non-conductive. Fortunately, our aircraft engines are equipped with dual magnetos for redundancy, and the probability of both magnetos failing simultaneously is extremely remote. Mag checks during preflight runup can detect gross ignition system failures, but in-flight mag checks are far better at detecting subtle or incipient failures. Digital engine monitors can reliably detect ignition system malfunctions in real time if the pilot is trained to interpret the data. Magnetos should religiously be disassembled, inspected and serviced every 500 hours; doing so drastically reduces the likelihood of an in-flight magneto failure.

The Bottom Line

The bottom-end components of our piston aircraft engines—crankcase, crankshaft, camshaft, bearings, gears, oil pump, etc.—are very robust. They normally exhibit long useful life that are many multiples of published TBOs. Most of these bottom-end components (with the notable exception of bearings) are routinely reused at major overhaul and not replaced on a routine basis. When these items do fail prematurely, the failures are mostly infant-mortality failures that occur shortly after the engine is built, rebuilt or overhauled, or they are random failures unrelated to hours or years in service. The vast majority of random failures can be detected long before they get bad enough to cause an in-flight engine failure simply by means of routine oil-filter inspection and laboratory oil analysis.

The top-end components—pistons, cylinders, valves, etc.—are considerably less robust. It is not at all unusual for top-end components to fail prior to TBO. However, most of these failures can be prevented by regular borescope inspections and by use of modern digital engine monitors. Even whey they happen, top-end failures usually result in only partial power loss and a successful on-airport landing, and they usually can be resolved without having to remove the engine from the aircraft and sending it to an engine shop. Most top-end failures are infant-mortality or random failures that do not correlate with time since overhaul.

The bottom line is that a detailed FMEA of piston aircraft engines strongly suggests that the traditional practice of fixed-interval engine overhaul or replacement is unwarranted and counterproductive. A conscientiously applied program of condition monitoring that includes regular oil filter inspection, oil analysis, borescope inspections and digital engine monitor data analysis can yield improved reliability and much reduced expense and downtime.

Mike Busch

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviator. Mike's book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.

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The opinions expressed by the bloggers do not reflect AOPA’s position on any topic.

  • Craig Fuller

    Thought this was one of the most thoughtful and informative articles I’ve seen on a topic that still makes most of us cringe…engine failure. I really like having two of these out there, but then I realize I may be twice as likely to have something fail. Thanks, Mike for some great insights! CF

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      Thanks, Craig. Though I fly a twin, I’m mindful that an engine failure in a piston twin on takeoff is more likely to kill me than one in a single. I think a good argument can be made that a Cirrus with its CAPS parachute system is potentially safer than a piston twin.

  • Jesse Blair Allred

    Very informative article. It really explains a lot. Thanks for all the info.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      My pleasure, Jesse.

  • Bill P

    Another great article by Mike Busch.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      Thanks, Bill.

      • Greg Wroclawski

        Mike,
        I suffered a catastrophic engine failure back in Oct of 2001 on the Continental TSIO-550 engine in my Malibu. The FAA red tagged the engine and a subsequent failure analysis by the FAA MIDO, the NTSB, and Continental concluded that it was a hole which burned through the top of the piston on cylinder #4 which originated from the cross in the position stamping on the number “4″ on the crown of the piston during the assembly process at the factory. A crack started at the “cross” of the number 4 and propagated across the piston centerline over the piston pin and eventually a hole burned through from the exhaust gasses forcing their way through the crack. This blew the oil overboard in a matter of minutes.
        I noticed this when the engine seemed a little rough in cruise and I saw the cyl #4 went cold on my engine monitor. I was at 17.5K ft over the Delaware Bay in the first few minutes I declared an emergency and decided to try for ACY because I calculated I had enough glide range and ACY has a 10K ft long runway and good emergency services incase I made a mess of it with a dead stick landing. Once I determined I had sufficient glide range (Malibus glide a 2.5nm/1000ft) I shut the engine down figuring I could restart it to develop a few seconds of power in case I botched the roll out to final. Even though I shut the engine down I it was still wind milling at about 1000rpm. It did this for close to 10min and it finally seized as I was gliding through about 8000ft. I made a text book dead stick landing at ACY with no bent metal just a scared family (wife and two kids). It turned out the engine had thrown a couple of connecting rods while wind milling in the glide.
        At the time of the failure my engine was 7 years old and had approximately 1000 hrs on it. I always operated the engine conservatively with a 6 point digital CHT/EGT engine monitor and a dual digital TIT gauge from EI.
        It tuned out mine was not the first failure. There was one approximately 2 weeks before mine and another in Nov of 2000.
        After the second failure Continental moved the position stamping process from being centered over the piston pin to the edge of the piston furthest away from the piston pin center line.
        I did some investigating and I hired Monty Barret from Barret Performance Engines to be present at the time of the engine tear down and failure analysis as an expert to represent me in case I wanted to persue legal action.
        The history behind the episode turned out to be this. Back in the early 80′s Piper designed the TSIO-520BE engine for the Malibu. It was their first engine with tuned induction and dual turbocharging. 10 years later it evolved into the TSIO-550 series of engines. Continental increased the displacement by stroking the 520 engine 1/4 of an inch. The cylinder assemblies were kept the same, so to accommodate the longer stroke and maintain the same compression ratio, they shortened the connecting rods a little and also dished the crowns of the pistons making them thinner. The stress riser cause by the position stamping process caused the crack to start. During the 90′s many Malibus were being converted from the factory TSIO-520BE engine to the TSIO-550C engine under STC. By the early 2000′s there were over 100 conversions flying.
        As best as I can ascertain there were at least another 10 similar failures of the TSIO-550C engine in the Malibu fleet as mine. All resulted in forced landings and some with bent metal but fortunately no fatalities. Finally in July of 2004 Continental issued a Critical Service Bulletin to bore scope inspect the piston crowns every 50 hours and to replace them with a newly designed stronger piston with no dishing of the crowns. At one of the MMOPA conventions a couple of years later one of the large Malibu shops showed a old style piston with a crack they found during a bore scope inspection that had NO position stampings in the piston crown. So cracks in the thin piston crowns didn’t always need a stress riser to initiate.
        Even though my engine was seven years old and had a 1000 hours on it, Continental gave me a generous warranty adjustment toward the purchase of a new engine and full core credit on my trashed core.

        • http://www.savvyaviator.com/ Mike Busch A&P/IA

          Thanks for the great post, Greg. I certainly recall Continental’s change in where they stamped the piston number, but I didn’t know the complete backstory on those failures so I appreciate the education.

          On our managed maintenance airplanes, we always have all cylinders borescoped every 100 hours at the same time as spark plug maintenance (cleaning/gapping/rotating) is done. My belief is that any time a top spark plug is removed for any reason, it’s crazy not to stick a borescope in the hole and look around. That would be akin to pulling a cylinder for some reason and not looking at the cam lobes and lifter faces. Yet I’m amazed how many engines have never been borescoped, or have had cylinders borescoped only when they have substandard compression results. I am absolutely obsessive and compulsive when it comes to the value of borescopy. I strongly suspect that had those TSIO-550s been borecoped ever 100 hour, few or even none of them would have fallen out of the sky.

          It’s been 11 years now since Continental issued SB03-3 that states repeatedly that a borescope inspection is “required” any time a compression test is done, yet the overwhelming majority of shops and mechanics are not doing this. If the compressions are above the master orifice thershold, then most mechanics consider the engine “good to go” and never ‘scope the cylinders. There are still shops and mechanics who are performing annual inspections on Continental-powered airplanes that don’t own a borescope! This is a perfect illustration of how much resistance to change exists in our maintenance infrastructure.

          Lycoming has been less vocal on the importance of borescopy, but of course it’s every bit as important for Lycomings as it is for Continentals.

          Your story is also a perfect illustration of the fact that many engine and aircraft design problems are only diagnosed and cured after there have been a significant number of actual failures in the field. Even the smartest aeronautical engineers and the most demanding test-cell runs can’t identify problems like the one that affected you. I have a rule-of-thumb that it takes about 10 years in the field for any new airplane or engine to get most of the bugs ironed out, and that early adopters are always unwitting beta-testers. I have always owned airplanes whose type certificates were well over 10 years old, but my firm manages plenty of airplanes that are in the beta-test phase. We manage about 10% of the Cirrus aircraft in the US, and those just reached my 10-year threshold in 2010. Sure enough, the Cirruses manufactured in the past several years seem to have most of the kinks worked out (finally), although in about 2010 Cirrus introduced the SR22T with a TSIO-550-K that is at least a partially new engine configuration that I suspect may need some more time in the field to work out its kinks.

          And so it goes. Thanks again for the great post.

  • Neil C

    An excellent article. However, my takeaway is that the majority of engine failures are infant mortalities. Therefore, if your engine is running well, oil pressure is good, compression is good, and there’s no metal in the filter, leave it alone. Replacing serviceable parts with newly-manufactured parts restarts the infant mortality clock, and may do more harm than good.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      You broke the code, Neil!

  • Rationalista2

    Thank you Mike Busch for your expertise and helping the rest of us properly maintain and operate these expensive machines. Your insight and experience is invaluable and I for one greatly appreciate it !

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      Thank you for the kind words.

  • Michael Kobb

    So, a question: your article says many times that bearings are always replaced at major overhaul. At the same time, you seem to be arguing that TBO is not a useful concept, and overhaul should be accomplished on condition.

    So, how do you know when it’s time to do the overhaul that is going to replace all of those bearings?

    • Greg Niehues

      I believe that’s the intent, yes. Metal reporting (by element) on the oil analysis will tell you which components are wearing and contributing that element to the oil. When you start seeing an increasing trend of bearing metals, you know the end is nigh for a bearing somewhere, which means they all need to go.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      The narrow answer to your question is that bearing distress can be identified through laboratory oil analysis(elevated levels of tin and/or copper) and oil filter analysis (numerous small flakes of metal that can be clearly identified as bearing material through scanning electron microscope evaluation). The broader answer to your question “how do you know when it’s time to overhaul?” will be the subject of a future blog post here.

      • Michael Kobb

        Super! I’ll look forward to that post, and thanks!

  • LawSci

    Great Overview. Just like my ’72 Datusn 240Z, the bottom end will last forever, while the top end is more questionable.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      In the 70s, I owned a cat Datsun 240Z, too, and rallied it competitively. That engine was absolutely bulletproof, except for the somewhat cranky dual carburetors that needed frequent adjustment. All in all, it was an outstanding car. If memory serves, I bought my new in 1972 and sold it to a friend in 1980, and act responsible for great recriminations afterward.

  • Robert Del Valle

    Thanks for the very informative article. The biggest challenge most aircraft owners have is to convince mechanics to follow Mike’s advice or the advice of other maintenance advisories. During my recent annual some rust was found on my engine mount. The mechanic advised it must be replaced. I informed him of the AC Advisory which allows rust removal with no more than a 10% reduction in the frame metal. He said, “I won’t do it. I don’t want an engine mount failure on my conscious.” So, I have a new engine mount coming. Sometimes you can’t blame the mechanics with a such a litigious society we live in.

    In reference to crankshaft replacement mentioned in Mike’s article, I previously owned a M4 Maule, my first airplane and fun to fly. I bought the M4 with 1035 hour TT and 125 hrs on the engine. the engine rebuild was due to a ground loop and prop strike by the original owner. After 175 hours on the engine I noticed oil residue on my windscreen. An inspection determined to be caused by a crack where the crankshaft meet the propeller flange. After reviewing the engine logbook I discovered the name of the engine shop. I called and learned the crankshaft was put back into service after passing a magnaflux test. The shop indicated the test is valid, but not foolproof. My suggestion is to always replace the crankshaft when there is significant damage to the prop. If its done during the rebuild, it is significant less expensive than after. My cost: Crankshaft 5500.00, bearings and seals 1700.00, rebuild bottom end 2500.00, engine removal and installation and freight 3000.00.

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      With respect to your engine mount, you probably should have sought a second opinion from another A&P. If you could find an A&P with a more reasonable attitude towards this minor engine mount discrepancy, you could have directed your IA to sign off the annual with a discrepancy, and taken the aircraft to the other mechanic to clear the discrepancy. If it was necessary to fly the airplane to another airport, it would be easy to obtain the ferry permit for that flight. Just because an IA says he won’t sign off your annual unless you do something unreasonable doesn’t mean you have to do that thing.

      With respect to your suggestion that a new crankshaft should be installed after any prop strike, I cannot concur. Most prop strikes are low-power prop strikes in which the chance of crankshaft damage is very small. Even in the case of high-power prop strikes, if the crankshaft is thoroughly inspected via both magnetic-particle and ultrasonic testing, it can safely remain in service. It sounds to me like your crankshaft underwent less than adequate NDT. A crack of sufficient depth to cause an oil leak at the front crankshaft oil seal should certainly have them picked up during NDT.

  • Bill Venohr

    Mike, I’ve been reading all your articles I come across and I’ve become more knowledgeable about my engine and in turn better able to monitor and maintain it. With the costs of flying, you are helping us do a better job as aircraft owners and operators. Thanks!

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      Thank you for the kind words, Bill.

  • Bryce S

    Very interesting article. I work as the chief pilot at a small company and we are sold on the idea of on-condition maintenance. One question, however, I’m curious why you religiously recommend the service of magnetos every 500 hours? It seems that from a safety standpoint there would be no issue with allowing them to run till failure. Thanks for the great post!

    • http://www.savvyaviator.com/ Mike Busch A&P/IA

      That’s a great question, Bryce. Logically, you would think that since our engines have completely redundant ignition systems, the magnetos could be safely run to failure. In a perfect world, that would indeed be the optimal strategy. However, in the real world, my observations is that pilots are not well-trained to deal with magneto failures, and almost always turn what should be a ho-hum event into a full-fledged emergency.

      In the relatively small population of the aircraft that my company manages (hundreds, not thousands), we had a half-dozen failures of magneto distributor gears during a one-year period. When the distributor gear fails, the magneto starts firing random spark plugs at random times and the engine pretty much goes berzerk. The appropriate pilot action in a situation like this is to identify the bad mag by switching to one mag, and if that doesn’t solve the problem, switching to the other mag. Once the malfunctioning mag is switched off, the engine runs normally on the other mag.

      However, not one of the six affected pilots had the presence of mind to do this. Each treated the berserk engine syndrome as an emergency. The pilots varied in experience from newbies to greybeard CFIs. One pilot experienced the failure at FL230 and had a full half-hour to think about the situation as he descended to an emergency landing, and in all that time it never occurred to him to try switching from BOTH to L or R.

      In a situation like this, redundancy helps only if the pilot knows how to use it. In a perfect world, pilots would be trained to deal with such failures and we could run the mags to failure. However, it appears to me that very few pilots are properly trained in this regard. That’s why I believe in doing 500-hour mag inspections. The mags are full of fragile plastic parts that seem to fail fairly often (at least as engine components go). Since pilots can’t be relied on to react to such failures properly, I think we need to try to prevent them from happening.

      Of course, in a truly perfect world, we’d have electronic ignitions instead of tractor magnetos full of fragile plastic gears and 60-year-old technology. The experimental airplanes mostly already do.

  • Brian Bishop

    Excellent article Mike. Although I lack experience with aircraft engines of any kind, I have extensive experience and knowledge of extremely high specific output automotive engines in motorsports. The methods you describe are precisely what happens in determining impending failure of components. The fatigue life cycle of those engines are pretty clearly understood and overhauls are done at certain periods to prevent catastrophic failures. In the GA operating environment, with the level of monitoring and inspection technology available, there is no reason I can see to do a major overhaul at fixed intervals. A change of this policy would be truly groundbreaking for owners and pilots of piston aircraft. Good luck!

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  • Tim Randall

    Thank you for the informative article Mike. I wish it could explore the high cam failure rates in more detail and possible solutions for failure prevention beyond the well known such as frequent oil changes even when not flown regularly, running single grades, parking engines if not flown for several weeks or months with a fresh oil change, and changing oil again after long periods of disuse before return to service, not reving our engines over 1000 rpm at start up like a lot or our pilots do. The cam is only operating at half the speed of the engine, so why is it failing so easily?

    We are having problems with cam and lifter failure on half time overhauls with Continental TSIO-520-M engines that don’t sit idle for long periods with the engine in service for a year and a half. This is from a highly respected and trusted major aftermarket engine rebuilder for type certificated engines in the industry.
    I don’t believe that the oil available for Type Certificated General Aviation AV-Gas Air Cooled Piston Engines contains adequate extreme pressure and antiwear additives that could help prevent this type of engine wear and failure.

    What could we be doing differently to prevent these frequent premature engine failures?
    Could we be suffering from temporary oil fuel dilution and shear back and not know it?
    Could the use of an industry popular fully conventional mineral based multi grade ashless dispersant oil that my people like to run in our engines year around, be failing to live up to it’s claims of maintaining a high level of protection in this application with the use of VI-improvers?
    Are we having failures because we are running this oil and it’s viscosity film strength may be too inadequate to provide proper protection when the oil hasn’t reached operating temperature while the engine is still warming up because the radial piston engine version of this oil has been accused to contribute to premature engine failures when run in radial engines due to the lower viscosity during engine warm up even though the area of engine failure in radial engines might be a different part of the engine than what we are dealing with?

    Could the close proximity of the cam and lifter face to the cylinder base area have a potential to overheating the oil film strength on the cam face if the engine experiences times of high CHT’s during operation even if the indicated oil temp is not getting too hot?

    We reached a dead end when approaching our our engine overhaul facility representative when trying to get help with this problem. OP, thank you If there is any helpful input you could give, we would appreciate it.

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