STOH vs SMOH

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DonaldDuck
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STOH vs SMOH

#1 Post by DonaldDuck » Mon Feb 22, 2016 3:13 am

I understand the difference lol STOH - since top overhaul (cylinders etc). SMOH - Major overhaul - they break open the bottom end, crankcase etc for rebuild if necessary

How does the legal and inspection framework work in Canada for small private planes? (i.e. Cessna 172, 152 etc)

if the engine is recommended to have an "overhaul" (TBO) at 2000 hours - is a Top Overhaul enough? What does "on condition" mean exactly?

For example I see a nice plane that has 4000 hours on the engine, with 500 hours STOH but never a major overhaul… (not i'm sure it could in theory be in great condition)… although is this something that could suddenly get flagged at an annual for rebuild?

Another example was a plane I saw where the owner's AME had kind of unofficially SMOH'ed the engine with a newly rebuilt crankshaft but because it wasn't done at a Aircraft engine facility (but a Truck facility!! lol) they just wrote that it had "new bearings installed" :)

Have you seen any planes with crazy high hours but never a full rebuild that are still air-worthy, (and have any kind of resale value)?


*Edit* - this is an interesting article arguing that time-based TBO doesn't make sense (except for Engine companies that sell a lot of $$$$$ parts and Mechanics who get a lot of business. Statistically planes with recent overhauls have more accidents and engine failures… ;) (and the author of this article owns his own AMO ….. )

http://blog.aopa.org/opinionleaders/201 ... ake-sense/
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Re: STOH vs SMOH

#2 Post by photofly » Mon Feb 22, 2016 8:16 am

For small privately registered aircraft maintained under CAR 625 Appendix B and C no hard time and calendar time maintenance intervals are enforced. You are never required to overhaul an engine regardless of the manufacturers recommended intervals.

You should do some work with the search feature. We beat this topic to death, for the hundredth time, just recently.
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Re: STOH vs SMOH

#3 Post by PilotDAR » Mon Feb 22, 2016 8:50 am

As Photofly says, there's a lot to be read on that topic here.

I would be leery of a 4000 hour engine. I bought my O-200 with 1600 on it, and ran it to 3500 with no problems, but I put the time on it, and I monitored it under the [then] new "on condition" program as I went along. It was safe when I took it apart, though there was crankshaft journal wear which I would not want to have hat go on for much longer.

If you're considering a nice plane with this engine, buy the plane, but not the engine. If the engine comes fro free, super, but don't pay any money for it! A 4000 hour engine has long since earned its keep, and retains core value at best. If its running, and you can fly it home, and around for a few months, bonus. You should be the onw flagging it for complete overhaul or replacement.

We are remarkably free in Canada to commit aviation. That freedom comes with the expectation that we take responsibility for our aircraft, with appropriate application of our wisdom. The wisdom on this is that engine is running on borrowed time. If it is well borrowed, you'll have some good parts which make it through overhaul - but budget the full overhaul soon.
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Re: STOH vs SMOH

#4 Post by DonaldDuck » Mon Feb 22, 2016 10:29 am

photofly wrote:For small privately registered aircraft maintained under CAR 625 Appendix B and C no hard time and calendar time maintenance intervals are enforced. You are never required to overhaul an engine regardless of the manufacturers recommended intervals.
good to know - and what If I want to commercially use the plane... are the Major Overhaul hours still mechanic determined or more fixed?
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Re: STOH vs SMOH

#5 Post by hangarline » Mon Feb 22, 2016 10:58 am

photofly wrote:You are never required to overhaul an engine regardless of the manufacturers recommended intervals.
This is not exactly true. At some point you WILL have to overhaul your engine. They don't run forever. And the term "Top overhaul" is misleading as well. Yes, you can overhaul the cylinders (top), but it in no way changes the total hours on the engine. The engine manufacturer will have an overhaul manual specifying the process required for overhaul and the mandatory parts replacement to be carried out at overhaul.
DonaldDuck wrote:good to know - and what If I want to commercially use the plane... are the Major Overhaul hours still mechanic determined or more fixed?

Commercial operators are required to have their maintenance program approved by T.C. , and like photofly said, this topic has been covered extensively in this forum before.









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Re: STOH vs SMOH

#6 Post by photofly » Mon Feb 22, 2016 11:37 am

hangarline wrote:
photofly wrote:You are never required to overhaul an engine regardless of the manufacturers recommended intervals.
This is not exactly true. At some point you WILL have to overhaul your engine. They don't run forever.
I'm going to stick with what I said. You will eventually have to carry out maintenance on the engine to keep it operating, but you're not ever required by Transport Canada to carry out the entire and full procedures described in the engine overhaul manual and that would be considered "an overhaul".
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Re: STOH vs SMOH

#7 Post by hangarline » Mon Feb 22, 2016 6:38 pm

So here is the scenario. Your engine has 4000 hours on it. It can't maintain oil pressure above 20 PSI, cylinder compressions are all 40/80, it's leaking oil at the crankcase seam. You take it to an engine repair facility. They disassemble it and tell you that the camshaft requires replacing, all crankshaft bearings are worn, cylinders worn past serviceable limits, crank case requires lapping to seal leaks. Why would you NOT overhaul it at that point? It would be the same cost to repair as overhaul.
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Re: STOH vs SMOH

#8 Post by AirFrame » Tue Feb 23, 2016 8:54 am

hangarline wrote:So here is the scenario. Your engine has 4000 hours on it. It can't maintain oil pressure above 20 PSI, cylinder compressions are all 40/80, it's leaking oil at the crankcase seam. You take it to an engine repair facility. They disassemble it and tell you that the camshaft requires replacing, all crankshaft bearings are worn, cylinders worn past serviceable limits, crank case requires lapping to seal leaks. Why would you NOT overhaul it at that point? It would be the same cost to repair as overhaul.
You're not getting what photofly is saying. There are no *regulations* requiring that you overhaul it. You would of course be silly not to, but you don't have to.
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Re: STOH vs SMOH

#9 Post by PilotDAR » Tue Feb 23, 2016 9:10 pm

There are no *regulations* requiring that you overhaul it.
When it comes right down to it, there are no regulations which require that you perform any maintenance on an aircraft. However, there is a rather all encompassing regulation requiring that a pilot is to assure that prior to their intended flight, the aircraft conforms to its type design ('not quite sure how a pilot would know that) and that the aircraft is fit and safe for flight. If the engine is baffed, it's obviously not fit and safe for flight. The "type design" for a GA piston engine will actually give you very little against which to measure fitness. It will probably state a required minimum oil pressure, and maximum temps, which can be useful in assessing the condition of an engine is a very general way. The other less common but happily simple standard for engine airworthiness might be found in an airframe type certificate data sheet, which could state a minimum and maximum static run up RPM.

In the mean time, we should not be maintaining our aircraft because we are driven by a regulation telling us to, we should maintain our aircraft because it's the right thing to do! "Maintaining" is defined in CAR 571, if there is any doubt as to what is intended....
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Re: STOH vs SMOH

#10 Post by hangarline » Wed Feb 24, 2016 8:45 am

PilotDAR wrote:When it comes right down to it, there are no regulations which require that you perform any maintenance on an aircraft
Umm...yes there is. It's called Canadian Aviation Regulations for a good reason. Sadly, if we did not have regulations, then some people would use that as a reason to NOT perform any maintenance. Of course it seems sometimes as if we are over regulated, but that is one of the reasons why Canada has a solid reputation in the industry.
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Re: STOH vs SMOH

#11 Post by PilotDAR » Wed Feb 24, 2016 8:43 pm

When it comes right down to it, there are no regulations which require that you perform any maintenance on an aircraft


Umm...yes there is. It's called Canadian Aviation Regulations for a good reason.
I don't know of a CAR which states a requirement to maintain an aircraft. The closest I know is 605.86, which states:
605.86 (1) Subject to subsection (3), no person shall conduct a take-off in an aircraft, or permit a take-off to be conducted in an aircraft that is in the person’s legal custody and control, unless the aircraft is maintained in accordance with

(a) a maintenance schedule that conforms to the Aircraft Equipment and Maintenance Standards; and.....
The CAR tells you that if you're going to fly it, you have to maintain it. You don't have to maintain it if you don't intend to fly it. Were it to be otherwise, there are a lot of derelict aircraft sitting around airports unairworthy, which are breaking the rules!
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Re: STOH vs SMOH

#12 Post by AirFrame » Thu Feb 25, 2016 8:44 am

hangarline wrote:Umm...yes there is. It's called Canadian Aviation Regulations for a good reason. Sadly, if we did not have regulations, then some people would use that as a reason to NOT perform any maintenance. Of course it seems sometimes as if we are over regulated, but that is one of the reasons why Canada has a solid reputation in the industry.
But in the specific case of a private owner and TBO on an engine, there is no regulation requiring that the engine be overhauled at TBO. You can run any engine until it seizes up on you if you want to. And yes, some people do.

Thankfully Lycomings are remarkably fault tolerant, and usually spend a lot of time telling the pilot that they're going south before they fail... Oil analysis helps track trends, Oil leaks that weren't there before, random coughing due to sticky valve seats or guides, etc. all tell a pilot that the time is coming. Figuring out exactly *when* to do it usually comes down to trading off the increasing time spent maintaining the small failures with the cost of a complete overhaul (or new engine).
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Re: STOH vs SMOH

#13 Post by hangarline » Thu Feb 25, 2016 6:11 pm

Okay, a couple of points here.
PilotDAR wrote:I don't know of a CAR which states a requirement to maintain an aircraft. The closest I know is 605.86, which states:
You answered your own statement in the same sentence.
PilotDAR wrote:The CAR tells you that if you're going to fly it, you have to maintain it. You don't have to maintain it if you don't intend to fly it.
Obviously. This is a forum for aircraft maintenance, so lets assume we are talking about maintaining aircraft that will be flying, otherwise we would be talking about maintenance on lawn ornaments or scrap metal.
AirFrame wrote:You can run any engine until it seizes up on you if you want to. And yes, some people do
Sadly, this is probably true. I can only hope that the idiot that does this flies solo over unpopulated areas.

Now back to the original poster.
DonaldDuck wrote:How does the legal and inspection framework work in Canada for small private planes?
Refer to CAR 605.86.
DonaldDuck wrote:if the engine is recommended to have an "overhaul" (TBO) at 2000 hours - is a Top Overhaul enough?
No
DonaldDuck wrote:Another example was a plane I saw where the owner's AME had kind of unofficially SMOH'ed the engine with a newly rebuilt crankshaft but because it wasn't done at a Aircraft engine facility (but a Truck facility!! lol) they just wrote that it had "new bearings installed"
Wrong, wrong and wrong. This AME is an idiot plain and simple!
DonaldDuck wrote:Have you seen any planes with crazy high hours but never a full rebuild that are still air-worthy, (and have any kind of resale value)?
Define "crazy high hours'. I assume you are talking about the engine. If it is the 4000 hour engine you mentioned, then resale value is very low. (on a 150, 172 or similar) If you ask 100 pilots this question, probably 95% would not want to buy the aircraft. Providing that the engine has serviceable compression, meets static rpm, no major oil leaks, serviceable oil pressure and has all maintenance entries documented and signed, then yes, it could be considered airworthy. The aircraft would have to have the same.
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Re: STOH vs SMOH

#14 Post by PilotDAR » Thu Feb 25, 2016 7:14 pm

mm...yes there is. It's called Canadian Aviation Regulations
Which CAR states that maintenance must be performed on an aircraft?

I have cited a CAR which states that flight in an aircraft not maintained in accordance with specified standards, is not legal. I presently own an aircraft which has not been maintained in accordance with the standards, and I intend to fly it. Before I fly it, I will assure that all maintenance is compliant, but I'm not in any rush whatever. In the mean time, there is no non compliance in this regard.
DonaldDuck wrote:
Another example was a plane I saw where the owner's AME had kind of unofficially SMOH'ed the engine with a newly rebuilt crankshaft but because it wasn't done at a Aircraft engine facility (but a Truck facility!! lol) they just wrote that it had "new bearings installed"


Wrong, wrong and wrong. This AME is an idiot plain and simple!
What's wrong with that? If the "SMOH" was "kind of" and "unofficial", it was not "official", and not any kind of overhaul (time since overhaul not zero'd in the log). That is clear. If the record of maintenance said that new bearings were installed, and that was done in accordance with the specified data for the task, that was proper maintenance, and I presume properly recorded in the logs. The description of the work accomplished would provide the required understanding to any reader, for the life of the logbook, as to what was done, and the relationship of the work accomplished to an "overhaul" (not at all close). That relationship [to overhaul] can be clearly understood by anyone reviewing the logs in the future - their purpose. More simply, the log will not show a time since major overhaul as zero, and the engine just keeps accumulating time in service, with work accomplished and recorded along the way - completely normal. If the AME who accomplished this work did it in accordance with the correct instructions, and recorded it with detail and correctly, they did exactly what they should be doing, and certainly are not an idiot! I split my engine, had the crank ground under, and was about to have the AMO reassemble it as a "repair", until I realized that in combination with the upper end work I had also done, the AME could sign out a zero overhaul, if I spent an additional $1000 on some mandatory replacement parts. I did that. But, it was my choice. The "maintenance" of replacing parts in the engine was not required, I chose it, and in doing so, accomplished maintenance with a greater perceived value in the future. It did not really affect the way the engine ran.

If a future person who has, or could come to have, technical responsibility for an aircraft feels that there is missing information about the work accomplished, they will not release the plane to service until questions are answered - which might mean an additional inspection/teardown/ or document review. The system works if the records are accurate.
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Re: STOH vs SMOH

#15 Post by AirFrame » Thu Feb 25, 2016 11:15 pm

hangarline wrote:
DonaldDuck wrote:if the engine is recommended to have an "overhaul" (TBO) at 2000 hours - is a Top Overhaul enough?
No
I don't think you can say "no" without having "enough" defined. Enough for what? To get to 1000 hours past TBO? Maybe. Enough to double TBO? Maybe not. There are way too many factors to say yes or no with any certainty.
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Re: STOH vs SMOH

#16 Post by photofly » Fri Feb 26, 2016 5:26 am

Some engines don't make to half their recommended TBO before they need serious work.
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