When aircraft owners, brokers and mechanics talk about engines, the word bulletproof comes up occasionally. We dont have a precise definition but we know what it means: An engine relatively free of operating foibles and likely to make TBO without undue strain.
On the other hand, no single adjective seems to describe the opposite end of the spectrum: Dog comes to mind, but when applied to some engines, its an insult to every canine that ever lived.
How ever you describe them, the world of aircraft engines is defined by extremes: The good is very good, the bad is usually unspeakable and often enough to cause the owner to take up boating or golf instead of flying. Fortunately for most of us, the middle ground is a broad, flat plain of acceptable performance and reliability. Maybe not an inspiration but not a nightmare, either.
Best and Worst
We thought it would be fun to survey the field of aircraft engines, with an eye toward naming the winners and losers. Which are the best and why? Which are to be avoided at all costs, unless you actually like dumping money into an airplane?
First, our definition of good is an engine thats likely to deliver on stated TBO with reasonable maintenance and no chronic weak spots that the factory never corrected. Because the airframe installation is critical, the winners are engines tolerant of an airframes peculiarities and those which have been well supported.
The dogs are the motors that werent a good idea to begin with, are tricky to operate and arent likely to make TBO no matter how careful you are. When overhaul is due, they may require a Kings ransom to rebuild. Unless youre made of money, youll want to avoid the latter.
Big Mill, Little Mill
Its no coincidence that small displacement engines seem to last longer than larger engines. They output less horsepower and thus have to tolerate less heat, vibration and related stress. For that reason, weve broken down our survey into three horsepower groups.
No mention of the best of the best can be made without visiting Lycomings carbureted O-320 engines. Virtually every model of the basic 320 uses the same crankcase, accessory case and cylinder configuration. Insignificant changes to accessories and drive pads, as well as minor deviations in compression ratios and hardware, hasnt affected the overall top rating of this series, regardless of installation.
These engines are predictable in the air and in the shop. Oil consumption is generally good and doesnt tend to sag much as the engine approaches TBO. Maintenance costs-especially for engines use infrequently-seldom reach the surprise stage.
As for flexibility, the O-320s have delivered good service in Piper, Beech and Cessna aircraft, most notably the Warrior and Cessna 172. The O-320-C series engines used in the Piper Apache are worthy of mention because they contain provisions for constant speed propellers, something homebuilders seeking a powerplant often consider.
Another best of the best in this class is the Lycoming O-235-Land -N series, primarily used in the Cessna 152. While this engineis prone to irritating plug fouling, the overall reliability ofthe 110 HP four-banger is exceptional. Maintenance needs above the routine include demand for valve adjustment-something other Lycoming models dont require. But the nuisance is outweighed by the predictability of overall operating costs.
Other top picks: The aging Continental C-series, 85 HP, four-cylinder engines found in the Cessna 120/140 and the Piper Cub. In a bare-bones configuration, the C-series engines are as simple as it gets, requiring only air, fuel and ignition but no starters or generators.
Naturally, there are some losers vagabonds and ceremonial washouts in this category. Among them is Lycomings early O-235-C series and any of the O-290 engines. Not to say these werent good engines in their day, theyre just permanently timed out and ready for the scrap heap.
Another loser is the Lycoming O-320-H2AD engine used in Cessna 172N. Introduced as a lightweight version of the -D-series powerplant, it was supposed to be manufactured on a new state-of-the-art automated line at Williamsport. The -H2AD suffered a torrent of bulletin and AD notes. Engines of this type that are in compliance with all mandated changes usually perform but once a bastard is labeled a bastard, its hard to shake the rep.
Finally, and at the risk of inciting a riot on the ramp, the engine that has outlived its usefulness-and its market appeal-is the Continental O-200-A, found in the Cessna 150 from 1959 through 1977. In its time, this 100 HP engine trained more pilots than any other made.
Operation was simple and maintenance predictable. The O-200s downfall came as more powerful alternatives from Lycoming emerged but a significant loss in reliability is due to electric starter drive failures and the cumulative effects of poor or nonexistent cylinder rework.
With demand for more power in a growing market, engine builders met the challenge. Lycoming bored the 320 to a 360 cubic inch displacement and increased the horsepower from the standard 150/160 to 180.
Adding a minimum of 20 HP to an already proven straight-valvedesign without the risks associated with a new engine made the investment a winner. Still, Lycoming reached a little with some redesign, introducing its 200 HP, fuel-injected IO-360. This wasnt the standard straight-valve powerplant but a new crankcase/ crankshaft/cylinder design than allowed higher compression ratios. The angle-valve 360 became a solid player in the mid-power market.
Continental also moved forward with the 1940s production of the E-series engines, available in 165, 185 and 225 HP versions. Many of these were installed in Bonanzas and Navions. The E-series engines were produced for over 20 years, after which a hesitant, albeit radical, change was made to the overall six-cylinder design, begetting the 230 HP O-470 engines, which some believe are the best Continental ever made.
These were a tad large to compete with Lycomings four-cylinder O-360s, so Continental came up with its own 360 series, with six cylinders. One version is the low-profile 210 HP IO-360 Cessna wanted for the 337 Skymaster. The marriage between the two was tormented at best. The six had problems with lightweight crankshafts and connecting rods and the cooling characteristics of the Skymaster caused overtemp problems.
Various models of these early Continental and Lycoming engines were upgraded as time went on and turbocharging was added to some for greater flexibility. But everything has its price and some changes spoiled an otherwise good powerplant.
In the mid-power category, our top picks include any of the Lycoming O- and IO-360-A series engines, with the exception of those with the dual magneto suffix D. Of particular merit is the undampered (no counterweights) 180 HP O-360-A1A, the -A1D, and the -A4M, such as used in the Piper Archer.
Injected versions of the 180HP IO-360-so-called straight valves- include the IO-360-B1E found in the early Piper Arrows and the IO-360-A1A used in the Mooney M20E and -F. Although not super performers, these motors have proven to be all but maintenance free. Another winner in this category is the Continental IO-360-KB engine installed in the Cessna 172XP. This 195 HP, six-cylinder engine gave the 172 a performance punch that far exceeded anything the Lycoming-powered Hawk could do.
When operated properly, the engine ran well and was smoother than the Lycoming, save for slight roughness caused by erratic fuel/air mixtures at low power and a problematic alternator drive gear.
The most dependable turbocharged version of this engine is the TSIO-360-KB,-GB, -LB and -MB engines used in the Piper Seneca and Mooney 231, among others. With all the upgrades for crankshafts, cases and cylinders, these engines perform well and are easy to maintain. In the boosted configuration, they require some cylinder work as the engine approaches TBO. Catastrophic failure is rare.
Without reservation, best of the best in this category has to be the 230 HP Continental O-470-R engine used in various models of Cessna 182s. This engine is the benchmark for smooth, reliable performance in the mid-power market without the expense of fuel injection.
The 470 is simple and has a proven history of predictable performance. Aside from the standard need for a top as the engine approaches the 900-hour mark, the O-470-R will fly through TBO with little difficulty. (Watch out for carb ice, however.)
Access behind the engine in the Cessna 182 is limited and oil pump and starter adapter maintenance might require engine removal. But this work is seldom needed and shouldnt play a role in a buy-sell agreement.
Other models of the 470 are equally reliable, even dating back tothe old O-470-L. However, casting changes to virtually every major component in the 470 mandate that a vintage engine be passed over for an -R engine with a born on date from the mid-1980s forward.
The O-470-S engine is identical to the -R except that oil squirt nozzles shoot engine oil to the back side of the low compression pistons-a needless function in that the -R engine worked fine without the squirts. Some maintain that the -S engine burns more oil because of this feature, but steel cylinder barrels in either will keep oil consumption reasonable.
The O-470-U engine installed in newer Cessna 182 aircraft was de-rated from full power RPM to reduce prop noise. Power loss was mitigated by an increase in compression ratio from 7.0 to 1 to 8.6 to 1. The change quieted the 470 but the added stress of low RPM and high compression ratios was hard on cylinder barrels, pistons and rings. As a result, the -U engine, while in the winner category, may be a candidate for a top overhaul sooner than the R engine.
Mess Up a Good Thing
More than a few otherwise reliable engines have fallen from grace because the engine manufacturers try to get something for nothing and airframe manufacturers want to get everything for nothing.
Light weight, low manufacturing costs and a half-hearted attempt to produce a new engine design prompted Lycoming to develop its 76-series engines found in late model Cessna, Piper and Beechcraft airplanes.
These engines have model specific crankcases, crankshafts, engine mountings and subsystems. In fact, little is used that would fit anything else in the IO-360 models. The 76 series engines include all left turning powerplants, with the exception of the LIO-360-C1E6.
While these engines are not difficult to maintain and can be predictable, we rate them as mediocre due to their lack of flexibility. Only a fraction of these engines were produced, compared to thousands of conventional 360 engines, thus internal engine parts tend to be very expensive. For instance, a camshaft for an LO-360-E1A6D costs at least $3000 compared to the $800 youd spend for a work-a-day 360 cam.
Also on the worst of the worst list is the Continental IO-360-A, -C, -D, -G, -H and all turbocharged versions of these engines used in various models of the Cessna Skymaster.
Cracked cylinders, broken crankshafts, leaking turbocharger exhaust systems, poor performance, hot running and unpredictable maintenance brand this engine installation one of the worst, in our view.
Big Bore Stuff
If you believe that Lycoming builds a tougher engine than Continental, its probably because Lycoming crankcases seem relatively crack free compared to TCMs 520 and 550 series. Further, the vague theory of shock cooling seems more applicable to heavily-finned Continental jugs than to those used on Lycs.
Regardless of the perception, the truth is that Continental high-horsepower engines exist in a delicate balance between strength and stress. Their operating characteristics-and ultimately the engines life expectancy-treads a fine line between heat produced and heat shed. The pilots participation in maintaining that balance on all fronts is critical.
Large-bore Lycomings, on the other hand, are less prone to damage from hamhandedness. The success of Lycomings is largely based on an equation that calls for avgas in quantities that would choke a Continental engine.
Where a Continental 520 wants critical tweaking of mixture and hawking of the gauges, the Lycoming 540 can roar along, eating oil, belching fire and smoke and consuming massive amounts of gas with few complaints.
Best of this class? Definitely the Continental IO-520-BB installed in the Beechcraft Bonanza and two of Lycomings IO-540 engines; the straight-valve IO-540-C and -D series and the angle-valve IO-540-K series used in the Saratoga. All of these engines are tough, produce plenty of power and can take a beating without showing much deterioration.
Continentals IO-520-BB engine is upgraded with the big main crankshaft, relocated alternator to the front of the engine and a simple fuel injection system. Given the Bonanzas better-than-average installation, the typical IO-520 isnt likely to need a top before reaching its 1700-hour TBO, Continentals problems with premature cylinder wear notwithstanding.
Lycomings IO-540-C, -D, and -K engines are rugged, simple and , most important, predictable in maintenance needs. With decent preventative care, regular oil changes and all but the most hamfisted mixture management, they tend to make TBO without a blip.
Once again, the dual magneto versions can and should be avoided-even though the dual magneto has shed much of its early difficulty. Acquiring an engine without the D suffix at the end of the model designation will avoid the dual mags.
Gotta consider turbocharged engines in the big displacement category. Simply hanging a Garrett blower on an IO-520 and pushing it into a tight engine compartment doesnt cut it when it comes to predictability, regardless of what the POH says.
Many engines in both camps have been subjected to ever increasing changes in power output and, ultimately, engine stress. Pushing to higher altitudes complicates the issue, due to less efficient cooling.
Best in this high-horse category is Lycomings 350 HP TIO-540-V2AD installed in the Piper Mojave. This engine is basically a standard O-540 engine, turbocharged beyond belief and equipped with all the normal accessories, except for one important difference: The cylinders are made of a unique aluminum alloy casting and fin design that yields a reliable, predictable powerplant for light twins without the nuisance of repetitive cylinder changes that dog other high output engines.
Interestingly, worst of the worst in this category-from the standpoint of unexpected expenses and God Almighty! predictions-is also a Lycoming. Specifically, several Lycomings. Losers in this class include the TIO-540-S1AD in the Turbo Saratoga, the turbostuffed IO-540 engines in the Aerostar series of airplanes and any Piper Navajo engine of 325 HP or higher. These engines run hot and exhaust valve guides-and valves themselves-are on a slow burn into oblivion from the first start to the last.
Last, the worst of the worst would have to include those ancient versions of all Continental TSIO-520 engines that havent been upgraded, reworked, carefully maintained or otherwise made more predictable by virtue of new castings and better materials.
Regardless of the engine model or aircraft installation, these engines can deplete the deepest pockets with a vengeance usually found only in divorce court. Not all of them have been overhauled to new specs. Be afraid, be very afraid.
As always, there are exceptions to every rule and occasional surprises, pleasant and otherwise. If all you ever do in airplane ownership is avoid buying an airplane with a known dog engine, youll have achieved what has eluded many a pilot.
Also With This Article
Click here to view “Special Mention Losers.”
-by Paul Brevard
Paul Brevard is editor of Aviation Consumers sister magazine, Light Plane Maintenance.