10 Lycoming Engine Parts Most Often Replaced — And Why They Fail

If you own or fly a Lycoming-powered aircraft, you already know one thing: these engines are tough. They power everything from the humble Cessna 172 in flight schools to high-performance singles used for cross-country travel. But tough does not mean trouble-free. Like any machine working hard in extreme heat and constant vibration, certain Lycoming engine parts wear out faster than others — and knowing which ones can save you serious money, time, and stress.

This guide breaks down the 10 most commonly replaced Lycoming engine parts. We will look at why each one fails, what warning signs to watch for, and how to get more life out of every component. Whether you are a student pilot curious about what is under the cowling or an experienced owner planning your next annual inspection, this is the kind of knowledge that pays off.

Key Takeaways

Understanding which Lycoming engine parts fail most often helps you move from reactive repairs to proactive maintenance. The most vulnerable components — including the camshaft, valves, pistons, and crankcase — tend to fail due to corrosion from inactivity, oil contamination, or thermal stress from poor operational habits. Regular oil changes (every 50 hours or 4 months), frequent flying, borescope inspections, and careful mixture management are the most effective ways to extend engine life and avoid costly, unexpected breakdowns.

How Do Airplane Engine Parts Wear Out?

It is easy to forget the hostile environment inside your engine cowling. Metal components are spinning at high speeds, exposed to extreme heat, and bathed in the corrosive byproducts of combustion. Wear in an aircraft engine is rarely about one single event — it is almost always a slow, cumulative process.

Operational stress plays a massive role. Every time you push the throttle forward, you are placing immense pressure on the internal components. That stress adds up across hundreds of flight hours.

Environmental conditions are equally aggressive. If you fly in a humid climate or near the coast, moisture is constantly working to corrode your engine's internals. High-altitude operations bring their own challenges around cooling and mixture management.

Maintenance habits — or the lack of them — are the final piece. Skipping an oil change or ignoring a small vibration accelerates wear significantly. The good news is that most of these failure modes are predictable and preventable.

Why Knowing the Weak Parts Can Save You Money

Aviation is not cheap. But there is a massive difference between planned maintenance costs and the surprise of an unexpected repair bill.

When a part fails without warning, it often triggers a domino effect. A failing bearing can send metal shards through the oil system, damaging the crankshaft and oil pump. What started as a small fix becomes a full engine overhaul — and a five-figure invoice.

Key insight: Proactive maintenance is almost always cheaper than reactive repair. An unexpected engine failure away from your home base doesn't just cost money — it grounds your aircraft until parts and labor arrive.

Knowing which parts are vulnerable lets you schedule preventative work during your annual inspection. It keeps your costs predictable. And most importantly, it keeps you and your passengers safe.

What Makes Lycoming Engines So Reliable?

Before we dig into what goes wrong, it is worth understanding why Lycoming engines are worth the attention in the first place.

Their reputation is built on simplicity. Lycoming designs are direct-drive, air-cooled engines with relatively few moving parts compared to modern automotive liquid-cooled engines. Fewer moving parts means fewer failure points. They also feature built-in redundancy — the dual magneto system, for example, means the engine keeps running even if one ignition source fails.

The materials are robust, engineered to withstand stresses well above typical operation. And unlike some competitors, Lycoming engines have an enormous installed base, which means decades of real-world data on exactly where they fail and exactly how to fix it.

That data, combined with proper owner knowledge, is a powerful combination. To understand how these engines fit into the broader aviation landscape, it helps to know what aircraft use Lycoming engines — the list stretches from two-seat trainers all the way to turbocharged high-performance singles.

Breakdown of the 10 Lycoming Engine Parts Most Often Replaced

1. Crankshaft

The crankshaft is the backbone of your engine. It converts the back-and-forth motion of the pistons into the rotational force that spins your propeller. It is massive and robust — but not immune to failure.

Why it fails

Crankshaft fractures are catastrophic but rare. When they do happen, the root cause is often corrosion from inactivity. When an engine sits idle, moisture strips the protective oil film from the journals, leading to pitting. That pitting creates stress risers where tiny cracks begin to form. Over hundreds of flight hours, those cracks grow — silently.

An unreported prop strike is the other major culprit. Even a minor strike can introduce microscopic cracks that propagate over time. Oil starvation can also cause bearings to seize, generating enough heat to shear the shaft.

Prevention tips

• Fly the aircraft regularly to keep oil on critical surfaces
• If the aircraft must sit, use proper preservation ("pickling") procedures
• Never ignore a prop strike — Lycoming mandates a tear-down inspection, and that rule exists for a very good reason

2. Camshaft and Lifters

If Lycoming engines have an "Achilles heel," most experienced mechanics will point here. The camshaft and lifters (also called tappets) are located high in the engine case, which means they are often the last to receive oil at startup — and the first to lose it after shutdown.

Why they fail

Corrosion is the primary enemy. After the engine stops, oil drains away from the cam lobes quickly. In humid environments or inactive engines, condensation forms on those surfaces. When the engine is next started, that microscopic rust acts like sandpaper, rapidly grinding down the hardened surface of the cam lobes and lifter faces. This process is called spalling. Once the case hardening is gone, the metal wears fast — sending metal filings through the entire lubrication system.

Prevention tips

• Fly at least once per week if possible
• Do not just "ground run" the engine — this introduces moisture without getting the oil hot enough to boil it off
• Use an oil additive like CamGuard, specifically designed to cling to cam surfaces during downtime
• At every oil filter inspection, watch closely for ferrous (magnetic) metal particles — these are often the first sign of cam or lifter distress

3. Bearings

Main bearings and connecting rod bearings reduce friction between the rotating crankshaft and the engine case. They are designed to last the life of the engine — if they receive proper lubrication.

Why they fail

Bearing failure is almost always an oil problem: starvation, contamination, or degradation. If oil pressure drops even briefly, the protective film between the bearing and the crankshaft disappears. Metal contacts metal, and damage happens in seconds.

Contamination is equally dangerous. Dirt, carbon, or metal particles from other failing components (like a spalling camshaft) can embed in the soft bearing material and score the crankshaft journals. Improper installation during an overhaul — wrong torque, slight misalignment — also sets the stage for premature failure.

Prevention tips

• Change your oil and filter on schedule — every 50 hours or 4 months, whichever comes first
• Monitor your oil pressure gauge every flight; even small trends matter
• Cut open the oil filter at every oil change — it is the single best diagnostic tool you have for catching bearing wear before it becomes catastrophic

4. Connecting Rods

Connecting rods link the pistons to the crankshaft. They live under constant tension and compression, reversing direction thousands of times per minute. It is one of the most mechanically demanding jobs in the engine.

Why they fail

Connecting rod failure is usually caused by bolt fatigue or hydraulic lock. If the rod bolts are not torqued to exact specification during installation — or if worn bolts are reused when they should have been replaced — they can fail under stress.

Hydraulic lock occurs when oil or fuel fills a cylinder and prevents the piston from completing its stroke. Forcing the propeller through during start-up in this condition can bend a connecting rod. A bent rod may run for a while, but fatigue will eventually finish it off.

Prevention tips

• Only qualified engine shops should perform bottom-end work, following current Lycoming service bulletins on rod bolts
• If you suspect hydraulic lock, do not force the prop through — remove the spark plugs first to drain the affected cylinder

5. Pistons and Rings

Pistons absorb the force of combustion directly. The rings around them seal the combustion chamber and control oil consumption. Together, they operate in some of the harshest conditions in the engine.

Why they fail

Heat distress is the most common piston killer. Detonation or pre-ignition — caused by incorrect timing, low-octane fuel, or a lean mixture at high power — can melt holes in piston crowns or fracture the ring lands. Rings themselves can wear out, break, or stick in their grooves due to carbon and lead fouling. When a ring breaks, it can score the cylinder wall, causing compression loss and high oil consumption.

Prevention tips

• Use a multi-probe digital engine monitor to track CHT (Cylinder Head Temperature) and EGT (Exhaust Gas Temperature) for every cylinder
• Avoid shock-cooling during descent
• Lean properly per your Pilot's Operating Handbook (POH) to prevent lead fouling and detonation

6. Cylinders

Lycoming cylinders are generally very tough, but they live in an environment of extreme, repeated heat and pressure cycling — and that eventually takes a toll.

Why they fail

Cylinders crack most often near the spark plug boss or the exhaust port, where thermal stress concentrates. Shock cooling — descending rapidly with low power — is a known contributor. Rapidly chilling hot metal stresses the material unevenly.

Glazing is a subtler problem. If a new cylinder is not broken in properly (run at sustained higher power to seat the rings), a glass-like surface forms on the cylinder walls. That glaze prevents rings from sealing, leading to chronic high oil consumption and low compression readings.

If you have recently installed a new or rebuilt engine, the Lycoming break-in procedure is critical reading — skipping or shortcutting the process is one of the most common ways new cylinders are damaged right from the start.

Prevention tips

• Perform regular compression tests and borescope inspections — a borescope can reveal scoring, cross-hatch wear, and early cracking long before a compression test catches anything
• Follow break-in procedures precisely for any new cylinder or freshly overhauled engine

7. Valves and Valve Guides

Intake valves let the fuel/air mixture into the cylinder. Exhaust valves let burnt gases out. The exhaust valve in particular operates at genuinely red-hot temperatures — and it shows.

Why they fail

Sticking valves are a well-documented Lycoming problem. Oil cokes (burns) onto the valve stem over time, causing it to seize in the valve guide. If a valve sticks open during operation, the piston can strike it — producing catastrophic, immediate engine damage.

Valve guides wear over time as well. When a guide becomes too loose (a condition called "bell-mouthing"), the valve wobbles instead of seating cleanly. A wobbling valve leads to a burned valve — hot combustion gases leak past the damaged seating edge like a tiny blowtorch, destroying the valve from the inside out.

Prevention tips

• Perform the Lycoming valve "wobble test" per Service Instruction 1485 at recommended intervals
• Use a borescope to look for asymmetric heat patterns on the exhaust valve face — uneven discoloration means it is not rotating or sealing correctly
• Manage ground leaning carefully to keep cylinder temperatures in a range that prevents both lead deposits and valve burning

8. Oil Pump

The oil pump is the heart of the entire lubrication system. If it fails, the engine can seize within seconds. There is no component more dependent on good maintenance habits upstream.

Why it fails

The pump gears wear gradually over time, slowly reducing their ability to maintain pressure. Sudden failure, however, is almost always caused by debris ingestion. Metal fragments from a failing camshaft or lifter can be sucked into the oil pump, jamming the gears or shearing the drive shaft. Cavitation — air bubbles in the oil caused by a low oil level or a leak in the pickup tube — can also pit the pump housing and reduce efficiency.

Prevention tips

• There is almost nothing you can do to the pump directly without opening the engine — so the best defense is early warning
• Track oil pressure trends across flights; a gradual drop over several hours is a red flag
• Regular oil filter inspections will alert you to metal generation before it destroys the pump

9. Rocker Arms and Pushrods

Rocker arms and pushrods are the mechanical messengers of the valve train. They translate the rotational movement of the camshaft into the linear movement that opens the intake and exhaust valves.

Why they fail

Wear is the main issue. Rocker arm bushings wear out, and the contact face that presses on the valve stem tip can become pitted. Pushrods can bend as a secondary result of a stuck valve — when the valve refuses to move, something in the train has to give.

Blocked oil passages inside the pushrods are another concern. If oil cannot flow up to the rocker box area, the rocker arms run dry — leading to squeaking, overheating, and accelerated wear.

Prevention tips

• During annual inspections, check rocker arms for side play and inspect valve tips for proper wear patterns
• Confirm pushrod tubes are sealed correctly to prevent oil leaks
• Verify oil is actually reaching the rocker box area — this is easy to overlook but simple to check

10. Crankcase

The crankcase is the structural foundation of the entire engine. It supports the crankshaft, anchors the cylinders, and houses the oil system. When it fails, the conversation quickly turns to full overhaul or replacement.

Why it fails

Crankcase cracks are the most common reason for replacement. They typically develop near the cylinder base studs or along the backbone of the case, driven by thermal cycling and vibration over thousands of hours. Fretting — micro-motion between the two crankcase halves — can occur when through-bolts lose their torque. This leads to oil leaks and, eventually, main bearing misalignment.

Prevention tips

• Balance your propeller dynamically — unbalanced props transfer vibration directly into the case
• Keep all through-bolts and cylinder base nuts torqued to specification during maintenance
• Inspect for oil seeps around case seams — these are often the earliest indicator of a developing crack

Signs a Lycoming Engine Part May Be Failing

Your engine rarely quits without warning. The key is knowing how to listen.

Unusual noises are the most obvious signal. A rhythmic knocking usually points to a rod bearing. A grinding or rattling can indicate issues with the starter, alternator, or valve train. A new noise always deserves investigation — never normalize it.

Instrument indications are your second line of defense. A drop in oil pressure, a rise in oil temperature, or an unexplained EGT spike all point to internal friction or lubrication issues. Monitor trends across flights, not just individual readings.

Metal in the oil filter is the most definitive diagnostic. Small amounts of carbon are normal. Finding ferrous (magnetic) metal, shiny aluminum flakes, or bronze particles is a serious warning. Cut your filter open at every oil change.

Increased oil consumption is a quiet but reliable indicator. If you used to burn one quart every 10 hours and now burn one every 3 hours, something has changed — worn rings, leaking valve guides, or a combination of both.

Rough running or RPM loss on the ground usually points to ignition or valve train issues. Address these promptly. The damage rarely stays contained.

How to Help Lycoming Engine Parts Last Longer

Extending your engine's life mostly comes down to consistent discipline. Here is what actually works:

Follow the manual. Lycoming's maintenance schedules are not suggestions. They were developed by engineers who understand these engines far better than any shortcut you might try.

Change your oil. Old oil turns acidic and fills with moisture. Change it every 50 hours or 4 months — whichever comes first. Consult Lycoming Service Instruction 1014 for the correct oil type for your engine and operating environment.

Use a borescope. This tool lets a mechanic inspect the inside of the cylinder without disassembly. It catches burned valves and scored cylinder walls long before a compression test raises a flag. There is no better early warning tool.

Fly regularly. Engines genuinely dislike sitting still. Regular flights boil off moisture in the oil and keep surfaces lubricated. Do not substitute ground running — it introduces moisture without getting the oil hot enough to burn it off. And never pull the prop through by hand to "move the oil around" — this can actually scrape the oil film right off the cam lobes.

Address issues immediately. A small oil seep and a minor vibration will not fix themselves. Every hour you delay makes the repair more expensive.

For a deeper look into each of these habits and the science behind them, this Lycoming engine maintenance guide covers proven techniques to extend engine life.

Factors That Influence How Long Parts Last

Two external factors have a major influence on part longevity beyond your maintenance habits.

Environment is the first. An aircraft based in a dry desert climate will generally see far less corrosion than one hangared near the coast in a humid, salt-air environment. If you operate in a corrosive environment, your maintenance intervals should be more aggressive — not identical to the baseline recommendations.

Operational habits are the second. How you manage the engine in flight shapes the long-term health of the pistons, cylinders, and valves. Smooth, consistent power changes protect against thermal shock. Proper mixture management prevents detonation and lead fouling. These are not advanced techniques — they are standard practice that pays dividends over time.

One often-overlooked factor is cold weather. Starting a cold-soaked engine without proper preparation puts tremendous stress on bearings and oil passages right when protection is lowest. The Lycoming cold weather starting guide walks through pre-heat procedures, winter oil selection, and starting techniques that protect your engine when temperatures drop.

Conclusion

Lycoming engines can deliver thousands of hours of reliable, safe flight. But that kind of longevity does not happen by accident. It is the product of consistent maintenance, smart flying habits, and a genuine understanding of where these engines are most vulnerable.

The Lycoming engine parts most often replaced — the camshaft, lifters, valves, cylinders, and crankcase — fail in predictable ways. Which means they can be monitored, managed, and in most cases, protected before they become an emergency.

Fly regularly. Change your oil. Use a borescope. Address small problems before they become large ones. 

And when you are ready to source quality Lycoming parts, engines, or connect with experienced aviation professionals, browse Flying411's engine and parts listings to find what you need from a trusted aviation marketplace.

Your engine is working hard every time you fly. Return the favor.

FAQs About Lycoming Engine Part Failures

What are the most common reasons Lycoming engine parts fail?

Corrosion from inactivity and oil contamination are the two leading causes. Operational errors — prop strikes, shock cooling, and running lean at high power — rank closely behind. The good news is that all three are largely preventable with proper habits.

How can I prevent crankshaft failures in my Lycoming engine?

Fly regularly. If you purchase a used aircraft, verify its maintenance and accident history thoroughly before signing. Regular oil analysis is the best ongoing monitoring tool for the health of the crankshaft's supporting bearings.

How does oil analysis help prevent engine failures?

Oil analysis identifies microscopic wear metals suspended in used oil. Elevated iron levels can signal rusting cylinders or cam wear. Elevated copper or lead points toward bearing distress. It is a cost-effective early warning system that can catch problems months before they become emergencies.

What is the difference between parallel valve and angle valve Lycoming engines?

Angle valve engines generally produce more power and operate more efficiently than parallel valve designs, but they are heavier and more complex to maintain. Parallel valve engines are simpler, lighter, and very common in training aircraft.

How often should I have a borescope inspection done?

Ideally, at every oil change — but absolutely at every annual inspection. A borescope inspection provides a direct visual health check of the cylinder walls, ring seal, and valve condition.

How do Lycoming engines compare to Continental engines for reliability?

Both are excellent powerplants with long track records. Lycoming cam placement high in the case makes them more susceptible to corrosion during periods of inactivity. Continental designs have different known weak points, particularly around their starter adapter. In practice, reliability depends far more on how the engine is operated and maintained than on the brand nameplate.

When should I consider a full overhaul instead of individual part replacements?

When multiple major components are showing wear simultaneously — particularly the crankshaft, camshaft, and cylinders together — a full overhaul often makes more financial sense than addressing each part individually. Understanding the difference between a factory rebuild and a field overhaul matters here too; the Lycoming rebuilt vs. overhaul guide breaks down the cost, lifespan differences, and which option fits which situation.