That's a rather inflated number....
It's close, I worked there 2 years and we did them twice, It would be 18 months at most. That plane flew pretty much daily with him in it.
Do Piston Engine TBOs Make Sense?
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It's close, I worked there 2 years and we did them twice, It would be 18 months at most. That plane flew pretty much daily with him in it.
Checkout_my_Six
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RotorAndWing
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Ted
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iFlyNothing
The real bugger is it can go either way. I've seen engines need majored at under 1,000 hours, and I've seen them make 3,000 or more.
docmirror
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I've always considered TBO to be a money equation. And it's not in the plane owners favor. Both big engine makers have conservative TBO numbers considering the wear cycles of the various components of an IC engine.
What we absolutely want to avoid is the catastrophic failure of an engine in flight. It's true, that the most dangerous engine is one that's just been hung with 0-150 hours on it. After 150 hours, pretty much all the teething problems have been wrought out of the engine, and it should go a long while before needing complete overhaul.
What's important is the trends in the wear items. The lowest life wear component is most aviation engines is the exhaust valve. On a typical big bore Conti the exhaust valve, seat, guide and seal might make 1600-2000 hours, but more than likely it's going to need some refreshing at 600-1200. Think about it, the exhaust gets blown with burning fuel vapor as it leaves the engine, so it's gonna be a high wear item. the highest wear item is the crankshaft main journal. It gets the best oiling, it is by far the largest, and in a well balanced engine, it absorbed the pulses from the cylinders and usually will motor along for 4-5000 hours with regular oil changes.
Avoiding catastrophic failures depends on monitoring to a great extent. I have an EGT per cylinder and I'm thinking of getting a CHT per cylinder soon. The trends in this area, combined with regular oil analysis should keep the probability of a in-flight failure very low, even on engines which are well over TBO. I have a big bore Conti, and I just factor one jug every two years into normal mx. If I get away with only one, I consider myself lucky. Now, as long as my warm oil pressure remains at a solid 45-50, and my CHTs run 360-390, I'm gonna go well past TBO, and just monitor things along the way.
What we absolutely want to avoid is the catastrophic failure of an engine in flight. It's true, that the most dangerous engine is one that's just been hung with 0-150 hours on it. After 150 hours, pretty much all the teething problems have been wrought out of the engine, and it should go a long while before needing complete overhaul.
What's important is the trends in the wear items. The lowest life wear component is most aviation engines is the exhaust valve. On a typical big bore Conti the exhaust valve, seat, guide and seal might make 1600-2000 hours, but more than likely it's going to need some refreshing at 600-1200. Think about it, the exhaust gets blown with burning fuel vapor as it leaves the engine, so it's gonna be a high wear item. the highest wear item is the crankshaft main journal. It gets the best oiling, it is by far the largest, and in a well balanced engine, it absorbed the pulses from the cylinders and usually will motor along for 4-5000 hours with regular oil changes.
Avoiding catastrophic failures depends on monitoring to a great extent. I have an EGT per cylinder and I'm thinking of getting a CHT per cylinder soon. The trends in this area, combined with regular oil analysis should keep the probability of a in-flight failure very low, even on engines which are well over TBO. I have a big bore Conti, and I just factor one jug every two years into normal mx. If I get away with only one, I consider myself lucky. Now, as long as my warm oil pressure remains at a solid 45-50, and my CHTs run 360-390, I'm gonna go well past TBO, and just monitor things along the way.
bnt83
Final Approach
It's a henning story......so not really...
In my experience "test bed" means sitting for weeks undergoing wiring changes... Also limited to VFR - DAY while holding the special airworthiness certificate.
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Nope, they were putting operational hours on a solid state gyro.
Checkout_my_Six
Touchdown! Greaser!
yup....and that would "depend" on the physics of failure....manufacturing defects, maintenance induced failure, wear-out, operating parameters, or corrosion.
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Seems like TBO is just an estimate of how long an average engine may last. A nice piece of data to use for making cost estimates or trying to agree on a sale price but nothing written in stone.
You see some cars need engine work in as little as 100,000 miles and some rare examples hitting 500,000 or more. Airplanes aren't going to be any different. How it's flown and how often, how/where it's stored, age, how good of a day the factory that built the parts was having, etc all change the longevity of the engine.
You see some cars need engine work in as little as 100,000 miles and some rare examples hitting 500,000 or more. Airplanes aren't going to be any different. How it's flown and how often, how/where it's stored, age, how good of a day the factory that built the parts was having, etc all change the longevity of the engine.
It's not even that, it really doesn't involve terminal life length, it's an economic life length that considers the cost of failure in a Strict Liability environment.That's why it's only mandatory in commercial service. Insurance can mitigate and control liability and cost in GA, not in Air Carrier service.
Dav8or
Final Approach
Most people do yank them at TBO. Most pilots and aircraft owners don't participate in web forums, don't spend endless hours reading on the internet about airplane maintenance and most don't even know who Mike Busch, or George Braly are, so they go by the same common wisdom that has been used since GA started, rebuild at or around TBO.
Basically, any time you operate an GA engine and take to the air, you are at risk no matter what the hours are. Airplane engines used to be so bad that the government thought it a good idea to establish a guideline on when to rebuild and inspect and engine before it fails in flight. This number is derived by actual performance in the field, not theory, or mathematical modeling.
As the engine shows longer and longer service life in practice, the manufacturers can petition to have the official TBO number raised. However, there is a great amount of variation from engine to engine and also how they are operated. Some fail at 500 hours and others go well beyond the official TBO number. Having said that, the manufacturers are not willing to raise the TBO above 2400 hours at the longest due to the fact of liability and also no doubt what they do see happening at rebuild time.
What does that tell you? Let's have a look at that chart you posted-
It shows that a lot of engines likely don't make it to TBO. Those engines, if they're lucky, get sent back to zero and start over again. See, there is an awful lot of variation in engines and some are better than others so the weaker engines show their weakness long before TBO. The fallacy of this chart is, like I said, most owners yank and rebuild at TBO no matter what, so the number of engines actually operated well beyond is very small so the number of accidents caused by the sub set is very small. Add to that that a great number of engines never make TBO for other reasons, like corrosion, prop strikes, or even ADs. Bottom line is you can't really trust this chart to tell you much at all.
Case in point- My plane. It is 48 years old and still has it's original engine. The engine now has something like 4500 hours on it, but it has never made it to TBO. It has been rebuilt four times though. Once for a Lycoming AD, once due to a gear up landing, once due to a discovered crankcase crack and once because it catastrophically failed in flight. Yep, threw a rod at 1500 hours and the pilot successfully put her down on a golf course. You can see how that charts statistics can be skewed.
The great thing is, this is America and here we generally allow people to make choices and hang themselves if they want. (Although less and less these days, but that's another thread!) In pretty much every other country I know that has significant GA except Canada (I think?), owners are required by law to rebuild at TBO.
Here we are allowed to operate as long as we like. Engine monitors, filter examinations, compression tests, oil consumption records, bore scoping and some say oil analysis (I'm not one of them) can really help you make up your mind when to yank the motor and also give you piece of mind when operating your engine.
In the end, it really is a crap shoot. I likely will never have to make the call on rebuilding at TBO because at the rate I fly that is a long, long time from now and it is more likely that the engine will fail for some other reason, I'll trade planes, or I quit flying by then. If you're buying a plane, I still think that 500-1000 hours on the engine is the sweet spot.
Hope this helps. Just thought I would throw a slightly different perspective than the very trendy attitude these days of just run 'er till she drops.
JHW
En-Route
no one can make that statement with a straight face. there is absolutely no way to have any idea. There are not even statistics that capture how many engines fail, much less when they are overhauled.
nddons
Touchdown! Greaser!
I get that engines can go past TBO. But would anyone pay a seller for an aircraft with an engine at or after TBO as anything but a run-out engine?
Even if compressions are good, etc., it would seem you shouldn't pay any more than a run-out for it. Am I wrong in my thinking?
TUPilot
Pre-takeoff checklist
I imagine a few people would, but personally I'm looking at an engine past TBO as a liability and my offer on the airplane would consider that an overhaul in the near future is likely. Of course, the engine isn't the only thing you look at and I might be willing to gamble a bit on a spotless plane with the avionics I want, but even then I'd only do it if I could come up with the cash for an overhaul if needed.
Granted, being able to come up with the cash for an overhaul on short notice isn't a bad idea regardless of engine time. You never know when you might need to cut that check!
But not much lower than a 2000hr engine, both are priced as run outs. That means any hours you fly past TBO are "profit", they are 'free' hours WRT value.
Dan Thomas
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For we Canadians the private owner has no hard time mandated against the engine. The commercial operator can use a formal on-condition program.
Many engine failures are due to peripheral equipment failures like magnetos that don't get the maintenance they need. The engine itself runs along fine as long as it gets some attention.
Dan
JHW
En-Route
no, not that many really have such a requirement for USE. However many countries have requirements that all appliances must be inside their TBO in order for the aircraft to be IMPORTED. Plenty of high-time aircraft have been flown to their new homes over the years with unplugged tach cables. It's a little ironic in some cases to be exporting a life-expired plane to a country that does not care about the FAA life limit on the wing spar, yet rejects the propellors because they had an inspection and reseal rather than an "overhaul"
Dav8or
Final Approach
You're right, there are no statistics kept, so no link to proof. However, consider the shear number of engine rebuilding facilities around the country. They all seem to keep plenty busy. This tells me that either there are a lot of engine failures, which ought to be concerning, or people are electing to rebuild. Pretty much all the people I have read over the years on various aviation forums that start out with "Should I rebuild..." usually end in the owner electing a rebuild.
In addition, if most are not rebuilding at TBO and there is a majority of owners that believe in running on condition, why is SMOH so important in resale values and why is there such a big discount for being near, or beyond TBO? It suggests that buyers and the people that advise them consider the engine finished at TBO.
You're right though, there is no way of knowing how many people are operating on condition and how many are opting to rebuild. It's up to the individual and their comfort level.
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N747JB
Final Approach
Great chart, very similar to one showing the death rate among people at various ages. Very few people die between 100 and 110 years of age, even fewer at 111-125! 
Most people do yank them at TBO. Most pilots and aircraft owners don't participate in web forums, don't spend endless hours reading on the internet about airplane maintenance and most don't even know who Mike Busch, or George Braly are, so they go by the same common wisdom that has been used since GA started, rebuild at or around TBO.
Basically, any time you operate an GA engine and take to the air, you are at risk no matter what the hours are. Airplane engines used to be so bad that the government thought it a good idea to establish a guideline on when to rebuild and inspect and engine before it fails in flight. This number is derived by actual performance in the field, not theory, or mathematical modeling.
As the engine shows longer and longer service life in practice, the manufacturers can petition to have the official TBO number raised. However, there is a great amount of variation from engine to engine and also how they are operated. Some fail at 500 hours and others go well beyond the official TBO number. Having said that, the manufacturers are not willing to raise the TBO above 2400 hours at the longest due to the fact of liability and also no doubt what they do see happening at rebuild time.
What does that tell you? Let's have a look at that chart you posted-
It shows that a lot of engines likely don't make it to TBO. Those engines, if they're lucky, get sent back to zero and start over again. See, there is an awful lot of variation in engines and some are better than others so the weaker engines show their weakness long before TBO. The fallacy of this chart is, like I said, most owners yank and rebuild at TBO no matter what, so the number of engines actually operated well beyond is very small so the number of accidents caused by the sub set is very small. Add to that that a great number of engines never make TBO for other reasons, like corrosion, prop strikes, or even ADs. Bottom line is you can't really trust this chart to tell you much at all.
Case in point- My plane. It is 48 years old and still has it's original engine. The engine now has something like 4500 hours on it, but it has never made it to TBO. It has been rebuilt four times though. Once for a Lycoming AD, once due to a gear up landing, once due to a discovered crankcase crack and once because it catastrophically failed in flight. Yep, threw a rod at 1500 hours and the pilot successfully put her down on a golf course. You can see how that charts statistics can be skewed.
The great thing is, this is America and here we generally allow people to make choices and hang themselves if they want. (Although less and less these days, but that's another thread!) In pretty much every other country I know that has significant GA except Canada (I think?), owners are required by law to rebuild at TBO.
Here we are allowed to operate as long as we like. Engine monitors, filter examinations, compression tests, oil consumption records, bore scoping and some say oil analysis (I'm not one of them) can really help you make up your mind when to yank the motor and also give you piece of mind when operating your engine.
In the end, it really is a crap shoot. I likely will never have to make the call on rebuilding at TBO because at the rate I fly that is a long, long time from now and it is more likely that the engine will fail for some other reason, I'll trade planes, or I quit flying by then. If you're buying a plane, I still think that 500-1000 hours on the engine is the sweet spot.
Hope this helps. Just thought I would throw a slightly different perspective than the very trendy attitude these days of just run 'er till she drops.
For what it's worth, exactly zero of the engines I've overhauled have been overhauled because the owner decided to overhaul them. There was something wrong with every single one of them that caused their demise.
Additionally, I've overhauled more engines that haven't made it to TBO than I have ones that have made it.
MBDiagMan
Final Approach
In the case of buying an aircraft that you are not familiar and comfortable with, I think your logic is sound.
MBDiagMan
Final Approach
^^^^^^^^^^^^^^^^^^^^^^^^
Here you go folks! This does not surprise me. If it ain't broke, don't fix it. In the case of aircraft engines, they are inspected and examined at least annually. This usually gives a bit of a heads up, before more serious problems occur. I'm sure that engines fail without warning, or at least not enough warning to get it on the ground, but when they get tired, there are some common warning signals that they give you.
Low compression..... warning sign. Metal in filter......warning sign. Oil usage.....warning sign.
Take care of it, and pay attention to it's warning signs. The chart earlier in the thread indicates that STATISTICALLY a 2,200 hour engine WITHOUT WARNING SIGNS, is safer than a 500 hour engine, ESPECIALLY if the 500 hour engine is showing a warning sign.
docmirror
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Cowboy - yeehah!
Well, here's the problem with that overhaul when something is wrong with the engine.
an overhaul is very invasive. You have a mech touching literally everything in the engine. The crank may be perfectly good, and well within dimensional spec being taken out, ground, edge radiused, maybe balanced, and possibly some other activity. Then you put it in with new bearings. Now mind you, this was a perfectly suitable crank, and maybe it had 1300 hours run time on it. You've just changed all the bearing fit for the case, and rod journals, you've also changed the way the gear drives the accessories, and also how the prop is bolted to the flange.
Just this one part being 'overhauled' changed dozens of things that can come back to bite you if it's not done exactly right. Of course, the mech is supposed to mic each journal, and each bearing, and each case flange for fitment, but the reality is about 0.5% actually do that. They get a box of 0.10" under bearings, and slap them in, then set the crank, and the case half together and a little oil then and torque.
The number of ways this can go sideways is just about a natural logarithm of the parts that were touched, and the person doing the touching. It can(and does) go wrong in the most unusual ways. Frex; I got a box of main bearings for an Avanti engine about 12 years ago. I started putting the crank in and I looked at one set of shells, and something about them was slightly different than all the others. I think the color was just a bit different, but I put the shell in and put a cap on it. Before I put the pan on, that bearing kept knocking at my head, so I took the journal cap off, and I stuck a little feeler gauge in there. Hmmmmmm, that doesn't look right. I got the box, and it was labeled right as 0.010" undersize(journal) but when I pushed the other bearing shell out and measured it, this one came up 0.030" under! Someone at the bearing mfg had put a 30 under shell set in the 10 under box. Oh boy was that tough to exchange.
The point is, that each time you touch something that didn't need to be touched, there's an element of risk. I would be inclined to inspect the crank, and bearings, and put them back in on a large bore Conti engine because I'm pretty sure that after 1300 hours of going around, it's going to go around for another 1300. The risk to changing all the dimensions and assembly are too great.
If an engine was overhauled because it had two leaky sets of rings, and three bad exhaust valves, then that's a mistake. We just had an example of a guy rebuilding two very expensive engines on an Aerostar, and both of them had mistakes that were caused by humans that messed up the engines on each side. I don't know how they even got installed on the plane and in the air because a good mech runs them on the test stand before it leaves the shop. If they were run on a test stand, and didn't make oil pressure under temp, it should never go out the door.
Of course someone is going to come on and pooh-pooh about mag points, or alternator brushes. Well, these are wear components that aren't intended to make TBO on the engine. For me - that's the same with the exhaust valve and seat. it's the weakest point of the whole engine but I wouldn't let the mech touch the internals of the case, if it was just exhaust and ring work. No way.
an overhaul is very invasive. You have a mech touching literally everything in the engine. The crank may be perfectly good, and well within dimensional spec being taken out, ground, edge radiused, maybe balanced, and possibly some other activity. Then you put it in with new bearings. Now mind you, this was a perfectly suitable crank, and maybe it had 1300 hours run time on it. You've just changed all the bearing fit for the case, and rod journals, you've also changed the way the gear drives the accessories, and also how the prop is bolted to the flange.
Just this one part being 'overhauled' changed dozens of things that can come back to bite you if it's not done exactly right. Of course, the mech is supposed to mic each journal, and each bearing, and each case flange for fitment, but the reality is about 0.5% actually do that. They get a box of 0.10" under bearings, and slap them in, then set the crank, and the case half together and a little oil then and torque.
The number of ways this can go sideways is just about a natural logarithm of the parts that were touched, and the person doing the touching. It can(and does) go wrong in the most unusual ways. Frex; I got a box of main bearings for an Avanti engine about 12 years ago. I started putting the crank in and I looked at one set of shells, and something about them was slightly different than all the others. I think the color was just a bit different, but I put the shell in and put a cap on it. Before I put the pan on, that bearing kept knocking at my head, so I took the journal cap off, and I stuck a little feeler gauge in there. Hmmmmmm, that doesn't look right. I got the box, and it was labeled right as 0.010" undersize(journal) but when I pushed the other bearing shell out and measured it, this one came up 0.030" under! Someone at the bearing mfg had put a 30 under shell set in the 10 under box. Oh boy was that tough to exchange.
The point is, that each time you touch something that didn't need to be touched, there's an element of risk. I would be inclined to inspect the crank, and bearings, and put them back in on a large bore Conti engine because I'm pretty sure that after 1300 hours of going around, it's going to go around for another 1300. The risk to changing all the dimensions and assembly are too great.
If an engine was overhauled because it had two leaky sets of rings, and three bad exhaust valves, then that's a mistake. We just had an example of a guy rebuilding two very expensive engines on an Aerostar, and both of them had mistakes that were caused by humans that messed up the engines on each side. I don't know how they even got installed on the plane and in the air because a good mech runs them on the test stand before it leaves the shop. If they were run on a test stand, and didn't make oil pressure under temp, it should never go out the door.
Of course someone is going to come on and pooh-pooh about mag points, or alternator brushes. Well, these are wear components that aren't intended to make TBO on the engine. For me - that's the same with the exhaust valve and seat. it's the weakest point of the whole engine but I wouldn't let the mech touch the internals of the case, if it was just exhaust and ring work. No way.
Dav8or
Final Approach
Since this thread is sliding off topic a little bit, I'll try this. Is the engine TBO number of any value at all when assessing a plane for purchase? Clearly airplane engines can't run forever, so if factory TBO means nothing, how do you assess how much life is left in an engine for the purpose of aircraft evaluation as a buyer? Is it safe to assume that if the plane in question has gone 2000 hours and the engine's bottom end has never been apart, that the engine will go another 2000?
It would seem that the engines that make TBO are the vetted lucky ones and should command a premium instead of a discount.
It would seem that the engines that make TBO are the vetted lucky ones and should command a premium instead of a discount.
Jimmy cooper
En-Route
I have no idea if flight schools run their engines this long but if they do you can be sure they follow carefully prescribed rules as to RPM's and maintenance. The average aircraft is what the manufacturer is attempting to measure and no one knows how these aircraft were operated so it's always a crap shoot. Some pilots are really hard on an engine, not letting it warm up properly, or worse, warming it up too much, lousy maintence, abusing it on climb out, on and on. Many owners could barely afford the airplane to begin with much less take care of it properly. On top of this, the seller often times will stare you in the eye and tell whopping lies. It's a crap shoot.
Since this thread is sliding off topic a little bit, I'll try this. Is the engine TBO number of any value at all when assessing a plane for purchase? Clearly airplane engines can't run forever, so if factory TBO means nothing, how do you assess how much life is left in an engine for the purpose of aircraft evaluation as a buyer? Is it safe to assume that if the plane in question has gone 2000 hours and the engine's bottom end has never been apart, that the engine will go another 2000?
It would seem that the engines that make TBO are the vetted lucky ones and should command a premium instead of a discount.
Those are two different matters, the financial world and the mechanical world. Financially the decision is pretty easy, it's all quantified. Apply cost of overhaul against TBO on a prorate basis where the market is calling Run Out value at 75% TBO.
Mechanical TBO isn't so quantifiable, it is best measured on a qualification basis.
This difference is what allows the savvy owner to mitigate their full cycle costs. If you buy cheap with 80% TBO engine in good condition at run out price, then operate that engine another 1200+hrs, do a 'name' overhaul and fly it another 75-125hrs and sell the plane, you will come out at you maximum financial advantage for your engine $$' A competing method is to keep your eyes out for a low time replacement engine to toss on for the sale. Fly the engine until you're ready to sell or it needs overhaul then swap. Even if you lose the core, if you got more than 1000hrs out of the old engine, you'll still be ahead.
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Jimmy cooper
En-Route
Since this thread is sliding off topic a little bit, I'll try this. Is the engine TBO number of any value at all when assessing a plane for purchase? Clearly airplane engines can't run forever, so if factory TBO means nothing, how do you assess how much life is left in an engine for the purpose of aircraft evaluation as a buyer? Is it safe to assume that if the plane in question has gone 2000 hours and the engine's bottom end has never been apart, that the engine will go another 2000?
It would seem that the engines that make TBO are the vetted lucky ones and should command a premium instead of a discount.
I would not assume anything, especially concerning an air cooled engine. If it's over 5-600 hours since major, and not from a reliable shop, I'll pass.
bnt83
Final Approach
As others have already said, its a crapshoot.
There is a story unfolding right now on a different forum about a IO550P that was disassembled after a cylinder failure and subsequent metal contamination. What they found is shocking.
Engine history:
Lives in Iowa
Last overhaul was in 2009
Hours since overhaul ~830
This is the second run on the crank, was ground .010 under in 2009.
They found corrosion pitting all the way around the crankshaft forward and aft of the propeller oil transfer hole.
One more interesting bit, he reports using camgaurd in it since the third oil change, and changes the oil every 35 hours.
There is a story unfolding right now on a different forum about a IO550P that was disassembled after a cylinder failure and subsequent metal contamination. What they found is shocking.
Engine history:
Lives in Iowa
Last overhaul was in 2009
Hours since overhaul ~830
This is the second run on the crank, was ground .010 under in 2009.
They found corrosion pitting all the way around the crankshaft forward and aft of the propeller oil transfer hole.
One more interesting bit, he reports using camgaurd in it since the third oil change, and changes the oil every 35 hours.
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Any other signs of Electrolysis? Does he run ROP? Why was the crank ground after one run through?
bnt83
Final Approach
The thread is focused on the crank so I can't say. The picture shows part of the aft side of the prop flange, it, along with the rest of the front main bearing area looks brand new with very obvious red pits.
I wonder what the total age of the crank is and where it has lived.
My very worthless guess is, it was ground .010 to remove corrosion.
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The thread is focused on the crank so I can't say. The picture shows part of the aft side of the prop flange, it, along with the rest of the front main bearing area looks brand new with very obvious red pits.
I wonder what the total age of the crank is and where it has lived.
My very worthless guess is, it was ground .010 to remove corrosion.
Yeah, if they ground it .010 due to corrosion, it wasn't dealt with properly IMO. If you have a corroded crank, you have a problem that is not a 'wear' issue. Most likely there is a metallurgy problem with the crank or an electrolysis issue (these can be tough to find). Another thing, do they Nitride these cranks? Was it nitrided after regrind?
I don't particularly like grinding cranks undersize.
AESpecialists
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AESpecialists
TBO is an actuarial value more than anything else. It's a risk based guess drawing from past statistics, estimates of life and chopped by fair margin for risk aversity.
It's a number that, taken by itself, is not especially valuable.
A 2000 hour TBO is roughly equivalent to 100,000 miles on a car. But the question is whether that 100k was put on a pizza delivery car by some punk kid, or a high-end salesman with a route in the western big square states. Not the best of analogies, given that 100k on new car is time for a tune-up. Think rather 100k on mid-60's 'Murrican Iron.
Lycoming will explicitly extend TBO by 10% if the time is put on within certain time perimeters, reinforcing the idea that flying is better than sitting. We work with a flight school that, under their own maint. program, routinely extends their TBO to 2800. On some of their airplanes they can do this in a roughly one calendar year.
Lycoming and TCM (CMC et C) both call out a 12year calendar TBO. This is sometimes the more important one really. Over time seals harden, corrosion forms and a backlog of AD's and SB's that must, or at least should, be complied with will accrue.
Far more important than TSMOH, is when and how those hours were put on. 500SMOH, with the overhaul done in 1999 is a MUCH MUCH worse bet than 1000SMOH done 2 years ago. The first will almost certainly be a rust ball inside that will be expensive to bring up to snuff, the second should be fine (unless it's been hauling skydivers - back to the pizza delivery analogy)
As other posters have mentioned, we tend to see more private owner overhauls as a result of high-time propstrikes, or a repair that uncovers a lot of bad stuff than we do from hitting the magic number. Flight schools and other commercial operations have their own requirements, and do keep closer to factory TBO.
I would love it if TBO were gospel, and everyone overhauled their engine .5 hrs before the magic number. More business for us and a busy shop is a happy and expanding shop. But, it's a number, and just one factor in a more complex equation.
It's a number that, taken by itself, is not especially valuable.
A 2000 hour TBO is roughly equivalent to 100,000 miles on a car. But the question is whether that 100k was put on a pizza delivery car by some punk kid, or a high-end salesman with a route in the western big square states. Not the best of analogies, given that 100k on new car is time for a tune-up. Think rather 100k on mid-60's 'Murrican Iron.
Lycoming will explicitly extend TBO by 10% if the time is put on within certain time perimeters, reinforcing the idea that flying is better than sitting. We work with a flight school that, under their own maint. program, routinely extends their TBO to 2800. On some of their airplanes they can do this in a roughly one calendar year.
Lycoming and TCM (CMC et C) both call out a 12year calendar TBO. This is sometimes the more important one really. Over time seals harden, corrosion forms and a backlog of AD's and SB's that must, or at least should, be complied with will accrue.
Far more important than TSMOH, is when and how those hours were put on. 500SMOH, with the overhaul done in 1999 is a MUCH MUCH worse bet than 1000SMOH done 2 years ago. The first will almost certainly be a rust ball inside that will be expensive to bring up to snuff, the second should be fine (unless it's been hauling skydivers - back to the pizza delivery analogy)
As other posters have mentioned, we tend to see more private owner overhauls as a result of high-time propstrikes, or a repair that uncovers a lot of bad stuff than we do from hitting the magic number. Flight schools and other commercial operations have their own requirements, and do keep closer to factory TBO.
I would love it if TBO were gospel, and everyone overhauled their engine .5 hrs before the magic number. More business for us and a busy shop is a happy and expanding shop. But, it's a number, and just one factor in a more complex equation.
petrolero
Pattern Altitude
Some engines don't even make it to TBO, much less beyond. It just depends on what happens in the calendar time between overhaul and the engine's tach reaching its "TBO" time.
Regular and relatively frequent usage, compression checks, regular oil changes with oil and oil filter analyses, regular bore scopes, top overhauls when needed, and just general engine maintenance are all things to do and watch before OR after TBO. All that and running the engine in a safe manner. The engine will tell you when it needs to be overhauled... if you're paying attention.
There is no inherent reason that engines require an overhaul at x hours. They need to be overhauled when conditions indicate they need to be overhauled.
Regular and relatively frequent usage, compression checks, regular oil changes with oil and oil filter analyses, regular bore scopes, top overhauls when needed, and just general engine maintenance are all things to do and watch before OR after TBO. All that and running the engine in a safe manner. The engine will tell you when it needs to be overhauled... if you're paying attention.
There is no inherent reason that engines require an overhaul at x hours. They need to be overhauled when conditions indicate they need to be overhauled.
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Interesting. Got a link to the thread so I can read about it?
Cutting the crank .010 on only the second run sounds excessive to me, but I don't know what is common on a 550.
You shouldn't have to grind it down at all.
bnt83
Final Approach
More detail, the crank was brand new in 2002 and has around 2200 total time
He's gonna call around to ask why they ground it in 2009.
bnt83
Final Approach
It's a subscription forum. At cessna.org
There's either an electrolysis problem, potentially a condition charged by the magnetos through the drive gears, or it was a junk crank from the factory. I don't know where they got their steel from. If I was replacing a crank, I'd have Crower make me a SuperLight off a billet and supply it as an "Owner Produced Part" Considering what a Continental crank costs, it'll be about the same to have one custom made better and stronger, maybe even a couple bucks cheaper.
The thing is one needs to determine why the degraded steel? If there is electrolysis set up, it doesn't matter how good the crank is, it will degrade. That a 2002 Continental Crank is of junk steel wouldn't particularly surprise me. I would also be looking at the alternator, that engine has the geared Alt up front right? Is it grounding through the crank? I'd look hard at the alternator and installation.
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