Age of Overhaul

[Stubby]

I'm almost positive this has been hashed out on this platform before, but I can't seem to find it in any searches. When shopping around, it seems like a lot of the listings I see are either very close to TBO, or very low hours SMOH. That being said, the listings with low hours since over haul a lot of times seem to be older overhauls with zero to minimal hours flown in the last year or two. I know there are certain risks associated with a motor that hasn't been operated regularly, but are they as prevalent as people make it sound? It seems that a lot of folks you talk to will tell you to run away from something that hasn't been flown 50hrs a year, but realistically, that's probably most GA planes. Does anyone have any first hand experience with buying something that has sat, whether that experience be good, bad, or indifferent? Thanks in advance for the knowledge to fall under this post...

[hubcap]

A friend of mine bought a plane like you describe. Less than 200 hours SMOH, but the plane had been sitting for a couple of years. He had to replace all 6 cylinders due to corrosion and pitting.

[Fly Boomer]

Other things equal, I would rather buy a regularly-flown airplane with an engine at TBO, than one with a fresh overhaul that has been sitting.

[Ragsf15e]

However, if you’ve got money available for the potential maintenance (worst case overhaul) and you can reach an acceptable price, you might be just fine.  You might get a really nice airplane… just go in with eyes open to the potential costs.

[Skates97]

19 minutes ago, hubcap said:

A friend of mine bought a plane like you describe. Less than 200 hours SMOH, but the plane had been sitting for a couple of years. He had to replace all 6 cylinders due to corrosion and pitting.

A friend bought a C that was mid-time but had only been flown some in the previous years. About a year in an oil change showed metal, the lifters were spalling among other things, had to have the engine overhauled and the plane was down 6+ months.

11 minutes ago, Fly Boomer said:

Other things equal, I would rather buy a regularly-flown airplane with an engine at TBO, than one with a fresh overhaul that has been sitting.

Agree 100%, you can at least negotiate the price with a run-out engine and likely get well past TBO if it has been regularly flown.

[c1tice]

I bought a K with 110 hours smoh in 6 years. I have had no engine trouble in the 200 hours I have put on it in 2 years, knock on wood. It sat for a while outside in FL. Discovered some corrosion below the window in the frame tubing. It was caught just in time. Point is just do a very through prebuy. Change the oil, cut the filter, remove inspection panels and interior side walls is my recommendation. If it looks good go for it, just have some $ in reserve. Something will come up. 

[PT20J]

There is no simple answer because there are too many variables. The major concern is corrosion. Was the airplane stored in Tucson or Palm Beach? Are the cylinders steel or chrome? Who did the overhaul?  Does it have plain, DLC or roller lifters? When was the oil last changed?

A thorough review of the logs and overhaul work order and complete inspection of the engine including borescope examination should provide enough information to a knowledgeable person to make a reasonable determination.

Still, ALL used engines (and used airplanes, for that matter) are somewhat of a crapshoot.

Good luck, and enjoy the adventure.

Skip

 

[A64Pilot]

Cylinder corrosion is easy to find with a borescope and in most cases I’ve found it, low compression is what made me look.

I think cylinder corrosion without it affecting compression isn’t an issue as it’s not corrosion that’s the issue, the rings clean it off nearly immediately, it’s the pitting that corrosion causes, but even then it’s not the end of the world unless really, really severe, if flown regularly more often than not I’ve seen motors with poor compression from corrosion recover quite a lot, and even if they don’t you likely have hundreds of hours before you really have to deal with it, so if you know about it and new cylinders are deducted from the sales price I think your way ahead.

On the flip side I’ve not seen corrosion so bad that it really dropped compression that could be cleaned up with honing, every time I’ve seen it the fix was new or overhauled cylinders.

Lycoming cams are an unsolved issue, a lot of people say it’s lifters not cams, but does it matter?, you’re splitting the case either way and that’s very often what trips the overhaul.

While Corrosion certainly could be a cause of cam failure it’s not the only one as flight school airplanes occasionally lose cams too.

Bottom line is you do the best you can, I’m not a big fan of oil analysis but I think flying an airplane I was looking at buying for at least an hour and sending in a sample could be helpful as well as cutting the filter and inspecting, but I don’t know how long results take? Can you pay extra for an expedited analysis?

You just have to buy the best airplane you can. My advice is don’t fall for pretty paint or glass panels, instead look deeper for a good motor and a corrosion free airplane.

Surely by now the market has shifted some and it’s more of a buyers market than it was just a couple of years ago.

[A64Pilot]

12 hours ago, Skates97 said:

A friend bought a C that was mid-time but had only been flown some in the previous years. About a year in an oil change showed metal, the lifters were spalling among other things, had to have the engine overhauled and the plane was down 6+ months.

I would say that it’s unlikely that sitting led to cam failure a year and I assume a 100 hours or so after purchase. Problems from sitting show up very quickly.

I think your friend fell victim to whatever it is that causes cams to fail on aircraft that are regularly flown.

[Utah20Gflyer]

This is a tricky issue because many owners think their plane with a 200 SMOH engine that was overhauled 20 years ago is a big asset and price their aircraft with that in mind.  I think things are slowly changing as people become more informed on what kind of engine history is actually good.   Many, including myself see that engine now as a big liability.  
 

So essentially you have two types of planes, one with a good history and one with a bad history and they are priced essentially the same.   So as a buyer it pays to know the difference and ignore the airplanes with bad histories.   The issue is a bit more grey than I’ve presented it and quantifying good and bad can be difficult but that doesn’t mean you can’t make an educated guess.  
 

If you want to keep your risk at a minimum then only consider the aircraft with obviously good histories.   You likely wont pay any extra.  

 

 

[PT20J]

From Lycoming SI1009

CALENDAR TIME PERIOD TBO
All engine models are to be overhauled within twelve (12) calendar years of the date they first entered service or of last overhaul. This calendar year time period TBO is to mitigate engine deterioration that occurs with age, including corrosion of metallic components and degradation of non-metallic components such as gaskets, seals, flexible hoses and fuel pump diaphragms.
CAUTION
CALENDAR YEAR TBO IS BASED ON ACCELERATED TESTING AND OVERALL FLEET SERVICE DATA. LOCAL CLIMATE CONDITIONS, STORAGE CONDITIONS, FREQUENT EXTENDED PERIODS OF INACTIVITY, PRESERVATION TECHNIQUES USED DURING INACTIVE PERIODS, AND FREQUENCY OF OIL CHANGES CAN AFFECT CORROSION OF METALS AND DEGRADATION OF NON-METALS.

[A64Pilot]

12 years has to be taken with a large grain of salt.

First you need to understand what TBO really means, it’s actually sort of a guarantee that if operated IAW the POH and MM that an engine will last at least that long, Hartzell prop is I believe also 12 years as I think many accessories are too.

I’d bet average airplane in the fleet was built in the 70’s, possibly the 80’s and average airplane is on their first overhaul. Mine is an 81 I think 2200 TT and 500 hours or so into its first overhaul and I think pretty average.

That makes her 41 years old and following calander TBO she would have gone through 3.5 engines.

Another way of looking at it is a frequently flown airplane flies 100 hours a year, most significantly less, maybe 50, so 20 to 40 years to hourly TBO and I think that’s pretty common.

Many countries enforce TBO, if you lived in one of them your buying an engine, prop and a bunch of accessories every 12 years.

Aging is hugely dependent on how it’s cared for and stored, particularly stored.

[DCarlton]

12 hours ago, PT20J said:

From Lycoming SI1009

CALENDAR TIME PERIOD TBO
All engine models are to be overhauled within twelve (12) calendar years of the date they first entered service or of last overhaul. This calendar year time period TBO is to mitigate engine deterioration that occurs with age, including corrosion of metallic components and degradation of non-metallic components such as gaskets, seals, flexible hoses and fuel pump diaphragms.
CAUTION
CALENDAR YEAR TBO IS BASED ON ACCELERATED TESTING AND OVERALL FLEET SERVICE DATA. LOCAL CLIMATE CONDITIONS, STORAGE CONDITIONS, FREQUENT EXTENDED PERIODS OF INACTIVITY, PRESERVATION TECHNIQUES USED DURING INACTIVE PERIODS, AND FREQUENCY OF OIL CHANGES CAN AFFECT CORROSION OF METALS AND DEGRADATION OF NON-METALS.

This is written like a requirement or mandate not a recommendation.  ???   Does Continental have something similar?  Does the FAA have a stated position?  

[EricJ]

3 minutes ago, DCarlton said:

This is written like a requirement or mandate not a recommendation.  ???   Does Continental have something similar?  Does the FAA have a stated position?  

Service Instructions or Service Bulletins are not required for Part 91 even if marked "mandatory".   If the FAA writes an AD and cites an SI or SB or whatever as the means of compliance, then it becomes required for the affected aircraft.  

[PT20J]

50 minutes ago, DCarlton said:

This is written like a requirement or mandate not a recommendation.  ???   Does Continental have something similar?  Does the FAA have a stated position?  

The FAA definitely has a position. The manufacturer can say anything they want but only the FAA determines the standards for airworthiness. That’s why everything in the POH is just interesting information EXCEPT the limitations section which must be approved by the FAA. If you exceed a limitation, you are in violation of FAR 91.9. 

Getting hung up on numbers is pointless. But there is a point. An engine that is 200 hr SMOH a year ago is not the same risk as an engine that is 200 hr SMOH 12 years ago (assuming the older engine was not stored in a preserved state).

[glbtrottr]

During Oshkosh, I noticed Mike Busch had an interesting seminar - in my opinion over the last 30 years it seems he has changed his opinion some after the advent of Walter, John and George but- longer conversation. Good luck to him with Savvy….

One of his lectures was “TBO5000-“ a story of how by circumstance, players involved and more led to an engine that made it to 5000 past TBO and more- as a combination of oil testing, dig Lsing engine behaviors and mechanical oversight.

I’ve overhauled engines in aircraft prematurely on at least 2 airplanes…and in fact I paid I advance for an overhaul some years back that I just received recently.

I’ve become more and more of the opinion that if you’re getting regular oil analysis, flying the engine regularly even after a long non flying spell, use an engine monitor, borescope and check compressions regularly, TBO is good for the Union workers at Lycoming but arbitrary as the lottery.

[PT20J]

I think TBO is a statistical thing. If a large number of engines are run regularly, conservatively, with regular maintenance, some will make TBO  and some will fall short, but the average should make or exceed TBO. The rub is that there is no way to know if a particular engine is average or not. As W. Edwards Deming used to like to say, “There is variation in everything.”

 

[ragedracer1977]

I bought a C model (o-360) in 2017 just at TBO.  I put about 800 hours on it 3 years.  Sold it to a friend in 2020. He put about 200 hours on it.  Then he sold in 2021.  Latest owner recently said it’s over 3300 hours since TBO.  Still running strong. I bought it fully expecting to overhaul it shortly.

 

my 310 has one engine at 2400 hrs (1800 oh time).  Runs great.
 

go figure

[PT20J]

Probably the best way to increase longevity is to run at lower power. Mike Bush told me he runs at about 65%. The airlines used to run the big radials less than 60%.

[A64Pilot]

After having a conversation with Pratt& Whitney I found out that TBO is not statistically driven, it’s not even derived from testing, it’s actually very close to the life limit of medicines etc. almost all meds are effective and chemically unchanged well beyond the date on the bottle, that date is simply a date that the manufacturer has picked quite honestly often arbitrarily as it’s a time line that’s common in the industry. If certain storage conditions are met most meds can be stored for an exceedingly long time. Same with engines.

‘It’s not an hour level where continued operation is deemed unsafe, different things drive TBO, it’s not as simple as it sounds.

You think pistons can be flown well beyond TBO? you ought to see what’s done with turbines that are cycled only once a day, that is they are only started once a day, idled during a short lunch etc as start cycles not time is more relevant for them. Hot section inspections are still done and parts replaced if necessary. It’s very common for Ag engine to exceed 10,000 hours or more, I’ve seen one at 15,000.

PT6-34A used to be I believe 3400 hours or so, there are a few pretty bogus STC’s that extend its TBO and I believe Pratt extended it to assist marketing a few years ago, but then they brought out single growth crystal turbine blades too.

Think about the STC’s for a second if you will. FAA allows a third party to extend the TBO of an engine that they didn’t manufacture, have no liability for and supply no parts for based on oil samples and a vibe check. So what is a TBO based on that? The STC holder has zero liability if the engine doesn’t make the extended TBO, but then Pratt has no liability if one doesn’t make factory TBO either.

TBO’s probably came from days gone past in order to try to ensure a level of safety for the flying public, but that’s long gone.

Modern big motors used on airliners have no hour limit, but are tracked by cycles often a cycle is one per flight but some are starting or each time an engine exceeds a set speed and components not the engine are traced and inspected or replaced at different cycles, in fact modern big motors are designed to never be removed from the wing.

The AH-64 and UH-60 engines for example were tracked flight cycle wise, several different cycles, starts, above a set Ng speed, above a temp set point etc, but the engines had no TBO, they were on condition, they stayed on the aircraft until performance decayed below a limit, then they were removed and sent to the engine shop for inspection and repair, but not overhaul.

If you dig into determining what a TBO is with the engine manufacturers as I have you come up with the answer that mostly it’s a point where in their opinion that an engine can be economically overhauled, a point where the expensive parts are still good and the clock can be reset by inspection and replacement of the consumable parts, bearings and seals, valves, guides etc.

Go well past TBO and if you wait until it’s making metal etc, it’s likely not to be economical to overhaul, it’s a throw away at that point.

Believe it or not but they are driven to keep or achieve a reputation of reliability. As most piston parts anyway are PMA’d they aren’t shortening TBO’s to sell parts.

Now big turbines are a completely different business model, they make pretty much no money on sales of new motors, the money is made supporting the engine through its life.

Edited August 4, 2023 by A64Pilot

[philiplane]

The quality of the steel inside the engine also matters. I would be less concerned about a low time engine overhauled 30-40 years ago, than a low time engine overhauled 10-20 years ago. We see much more pitting corrosion in newer builds than old ones. I am monitoring an IO-540 that was a Lycoming factory reman in 1972. It now has 1800 hours on it. Spent half its' life in Southern California, the rest in Pennsylvania and now Florida. Zero internal corrosion. Excellent compressions. All the external rubber hoses, accessories, etc, have been replaced in the past 10 years. The engine looks and performs like new. It's had 25 hour or 6 month oil changes its' whole life. And it's been on Camguard since that came out about 20 years ago. 30 years worth of oil analysis records show no issues. 

I expect this engine to keep going until the cylinders start to show wear or the exhaust guides get loose and burn a valve. Which so far is well into the future.

On the other hand, I've had many problems with much newer engines (all built new after 1996) having pitted cams, rusted cylinders, and valve problems. Continentals are especially prone to internal rust. During the recent crankshaft counterweight AD, one shop found pitted lifters on a 2023 Cirrus with less than 50 hours on the engine.

Edited August 4, 2023 by philiplane

[Fly Boomer]

14 hours ago, PT20J said:

Probably the best way to increase longevity is to run at lower power. Mike Bush told me he runs at about 65%. The airlines used to run the big radials less than 60%.

I had not heard that percentage, but I remember him saying he is way more interested in longevity than speed.

[ragedracer1977]

On 8/4/2023 at 1:04 PM, Fly Boomer said:

I had not heard that percentage, but I remember him saying he is way more interested in longevity than speed.

I’ve started running my big bore turbo Continentals at 45% power give or take.  I don’t give up much speed.

i fly to San Antonio several times a year.  70% gets me there in 4.1-4.6 (depending on winds) “chock to chock” and burns about 145 gallons.

45% gets me there in 4.4-4.9.  20 minutes give or take extra flight time, but I only use 115 gallons.

i flew non stop from Rockport TX (near Corpus Christie) and only used 135 gallons. At 75% I’d have had to stop for fuel and it would have taken me longer to fly “faster”.

 

Edited August 6, 2023 by ragedracer1977

[Fly Boomer]

10 hours ago, ragedracer1977 said:

I’ve started running my big bore turbo Continentals at 45% power give or take.  I don’t give up much speed.

i fly to San Antonio several times a year.  70% gets me there in 4.1-4.6 (depending on winds) “chock to chock” and burns about 145 gallons.

45% gets me there in 4.4-4.9.  20 minutes give or take extra flight time, but I only use 115 gallons.

i flew non stop from Rockport TX (near Corpus Christie) and only used 135 gallons. At 75% I’d have had to stop for fuel and it would have taken me longer to fly “faster”.

Pilots with faster airplanes (like your twin and my Rocket) are often obsessed with “how fast” but, as you point out, until you get up into turbine speeds, it really doesn’t make that much difference in trip time.  And 30 gallons of gas is a big incentive to slow down, not to mention the cost of overhaul on a big-bore Continental.

Regarding the fuel stop.  Mike Busch uses the same technique you do.  He watches the fuel remaining at destination number, and keeps pulling back power until it gets up to a comfortable number.

[Fly Boomer]

10 hours ago, ragedracer1977 said:

I’ve started running my big bore turbo Continentals at 45% power give or take.

Do you have TSIO-520s in your airplane?  What numbers do you run to get down to 45% power?  LOP?