First A/C purchase..... question about terminology

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ogopogo
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First A/C purchase..... question about terminology

#1 Post by ogopogo » Wed Oct 07, 2015 7:37 am

I found a US link that talks about the difference between SMOH (main) and SFOH (factory). In Canada, when an engine is "zero timed", does this mean it was sent back to the actual,manufacturer? The article I refer to says SMOH can be done "by anyone" - obviously an AME, but what's the difference between SMOH and SFOH?

I am looking at a plane which was SMOH'ed (LOL) and has less than 150hrs on it since then. But the engine is not stated to be zero timed, ie the clock doesn't reset if it was SMOH, only SFOH??

In Canada, where are aircraft engines usually sent to be zero timed?
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photofly
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Re: First A/C purchase..... question about terminology

#2 Post by photofly » Wed Oct 07, 2015 8:24 am

The clock resets at any major overhaul. Hence "Time Since Major Overhaul". A major overhaul is a complete stripdown and rebuild, per the relevant service manual, and any part that are worn beyond limits are replaced. Broadly speaking, anything that isn't worn beyond the given limits can be reused.

Something like the crank case can be reused for several overhauls and therefore may have been in the air for 10,000+ hours and some decades, even on a zero-time engine.

Any AME can overhaul a small piston engine and "zero time" it - but whether that's a wise choice or not depends on your trust in the AME's expertise. I believe Mike Busch makes the point that only a specialist engine shop should be removing more than a single cylinder on an engine, in his opinion.

Lycoming itself offers:

Factory New
Factory Overhaul
Zero-time factory rebuilt
http://www.lycoming.com/Lycoming/PRODUC ... rhaul.aspx

These are all zero-time engines, with a greater or lesser number of used parts put back into them. All the parts will have passed the relevant dimensional (and other?) tests and are considered appropriate to put back into an engine.

Continental offers:
Factory New
Factory Rebuilt

Then there are the various options from Penn Yan, and all the other "name" engine overhaul houses.
As well as whatever a random AME wants to whip up in his hangar.

If, however, you just replace all the cylinders with new and don't open the case, inspect/replace the crankshaft and all the interior bits - then the clock doesn't reset on the engine.
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groncher
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Re: First A/C purchase..... question about terminology

#3 Post by groncher » Wed Oct 07, 2015 8:49 am

Careful here, the time since overhaul resets to zero, the engine cannot be zero timed. The time since new remains just that.
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ahramin
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Re: First A/C purchase..... question about terminology

#4 Post by ahramin » Wed Oct 07, 2015 9:29 am

Lycoming offers a factory new overhaul that resets the engine to new. New serial number, new logbook. I think on a 360 it's about 8k cheaper than buying a new engine.
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Re: First A/C purchase..... question about terminology

#5 Post by photofly » Wed Oct 07, 2015 12:10 pm

ahramin wrote:Lycoming offers a factory new overhaul that resets the engine to new. New serial number, new logbook. I think on a 360 it's about 8k cheaper than buying a new engine.
That's a good point, isn't it? A factory new overhaul is a zero time engine, but it's not going to be all new parts.

Here's some other background reading:
http://www.avweb.com/news/usedacft/189377-1.html
http://www.avweb.com/news/maint/185049-1.html
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ahramin
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Re: First A/C purchase..... question about terminology

#6 Post by ahramin » Wed Oct 07, 2015 3:23 pm

photofly wrote:Here's some other background reading:
http://www.avweb.com/news/usedacft/189377-1.html
Not a very useful article. The advice contained revolves around the misguided premise of whether or not the engine will get to published TBO:
For example, if an engine has been used 1,700 hours out of a 2,000-hour TBO, the time remaining could serve the new owner for many years, depending on how many hours a year he or she flies ... If the compression starts to drop suddenly after 100 hours and the mechanic determines it is necessary to overhaul the engine early.
Recommended TBO hours has been demonstrated to be a completely useless number for predicting engine failures. Similarly compression tests are no great indicator of cylinder health.
Typically, if an engine was overhauled properly and has flown 150 to 200 hours with no problems, its chances of reaching TBO are better than one that has had major problems early.
Ignoring the comment about reaching TBO, this is true in sentiment if not in specifics. The NTSB study by Nathan Ulrich on engine failures in piston aircraft shows that almost 40% of all engine failures happen in the 0-500 hour mark, followed by 25% in the next 500-1000 hours. So almost 2/3 of all engine failures happen in the first 1000 hours.

I can see what you are getting at with the second article though: quality of the overhaul. New limits vs service limits. I'd be more concerned about how often the engine in currently being flown, oil analysis, boroscope, ect.
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Re: First A/C purchase..... question about terminology

#7 Post by ogopogo » Wed Oct 07, 2015 7:09 pm

Thanks everyone for the replies and comments - much appreciated. As you can tell, I am struggling a little in trying to independently understand what I'm potentially getting myself into with this aircraft purchase. The TTE is around 1900 hrs (O-320) but was "overhauled" 12 years ago and since has averaged only about 10hrs per year.

The work done was basically to remove the cylinders, which were found to be in spec. New rings and exhaust valves and guides were done.

So this is what I'm looking at - not too sure how to judge it. The plane is in O-M. If you search around you'll find it.
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Re: First A/C purchase..... question about terminology

#8 Post by AOW » Wed Oct 07, 2015 9:53 pm

ogopogo wrote:Thanks everyone for the replies and comments - much appreciated. As you can tell, I am struggling a little in trying to independently understand what I'm potentially getting myself into with this aircraft purchase. The TTE is around 1900 hrs (O-320) but was "overhauled" 12 years ago and since has averaged only about 10hrs per year.

The work done was basically to remove the cylinders, which were found to be in spec. New rings and exhaust valves and guides were done.

So this is what I'm looking at - not too sure how to judge it. The plane is in O-M. If you search around you'll find it.
I would be very careful with a Lycoming that only flies 10 hrs per year for more than a decade.
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Re: First A/C purchase..... question about terminology

#9 Post by nbinont » Wed Oct 07, 2015 10:22 pm

ogopogo wrote:The TTE is around 1900 hrs (O-320) but was "overhauled" 12 years ago and since has averaged only about 10hrs per year.
TTE should not have a significant effect here. Most important is SMOH (in your case ~120hr) and the regularity of use during this period (sitting for long times between use is undesirable).

I would recommend getting a good AME's opinion.

If you want to learn a lot of the technical side, spend some time listening to these: https://www.savvymx.com/index.php/resources/webinar .
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Re: First A/C purchase..... question about terminology

#10 Post by ahramin » Wed Oct 07, 2015 11:13 pm

Sounds like the SMOH is 1900, not 120. The 120 was a top overhaul, which isn't an overhaul at all, just cylinder work.
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Re: First A/C purchase..... question about terminology

#11 Post by nbinont » Thu Oct 08, 2015 3:07 am

ahramin wrote:Sounds like the SMOH is 1900, not 120. The 120 was a top overhaul, which isn't an overhaul at all, just cylinder work.
Good point. If that is so, then ogopogo should realize the TBO of the engine is listed at 2000hr, and should be valued as approximately run out. It could end up lasting a good while yet, but without me having seen the plane, I would say ogopogo should anticipate needing to do some significant work/overhaul on the engine in the near to medium term.
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Re: First A/C purchase..... question about terminology

#12 Post by ogopogo » Thu Oct 08, 2015 5:09 am

The aircraft is listed as follows :

3800 TTAF
1900 TTE
119 SOH (done in 2003)
0 New prop

ACF-50 treated
Currently engine inhibited, dehydrator plugs.
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Re: First A/C purchase..... question about terminology

#13 Post by photofly » Thu Oct 08, 2015 6:06 am

To this untutored eye, giving some low time "since overhaul" looks like a deliberate attempt by the vendor to mislead. At best, without saying what "overhaul" means, you should probably ignore that number.

The engine is run-out. It should be priced as such. It might run another 2000 hours with whatever was done 190 hours ago, or it might not - but as airplane pricing is calculated the engine is done.
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Re: First A/C purchase..... question about terminology

#14 Post by Heliian » Thu Oct 08, 2015 3:33 pm

First off, ACRONYMS ARE BULLSHIT!

Show me the logs and I'll decipher the numbers from the work done and sign-offs. Remember, an aircraft is only as good (or bad) as it's logs. There was another thread on here about acronyms and the general rule is that there is no general rule. If you're buying your first a/c, get someone knowledgeable to help you.
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Re: First A/C purchase..... question about terminology

#15 Post by ogopogo » Fri Oct 09, 2015 12:40 pm

ahramin wrote:Sounds like the SMOH is 1900, not 120. The 120 was a top overhaul, which isn't an overhaul at all, just cylinder work.

What exactly "zero times" and engine, then?
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Re: First A/C purchase..... question about terminology

#16 Post by photofly » Fri Oct 09, 2015 12:57 pm

A major overhaul, conducted according to the relevant service manual, resets the SMOH clock - because the time "Since Major Over-Haul" becomes zero.

If you're talking about any other kind of clock, you have to say what "clock" you're talking about. "Time since new" is the hours since the engine was assembled at the factory and given a new serial number and data plate. As far as the owner is concerned, nothing resets that - if you want a zero-hours-since-new engine, you get one by buying a new engine from the manufacturer. "Time since overhaul" has no meaning because there's no definition of just "overhaul".

In the world of commercial operations it's a requirement to give a major overhaul to piston engines at intervals specified by the manufacturer and approved by the relevant airworthiness authority (typically the FAA) - or otherwise have special approval to operate beyond that interval. The value of an engine therefore diminishes with the number of hours since the last major overhaul. A typical usage of the phrase "zero-time" would mean it has just received a major overhaul, and the clock (hours SMOH) has been reset to zero.

For the purposes of private flying, no hard-time limits apply to small piston engines, so any and all clocks - time since new, time since major overhaul - are advisory only.
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Re: First A/C purchase..... question about terminology

#17 Post by ogopogo » Fri Oct 09, 2015 1:34 pm

Thanks, interesting. OK let me be more specific:

A/C has 1900 hrs on the O-320. It gets overhauled by the book. Time now 0h SMOH.

What exactly got done to the engine? I'm the AME doing the work. What procedures have I done.
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Re: First A/C purchase..... question about terminology

#18 Post by photofly » Fri Oct 09, 2015 2:20 pm

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Re: First A/C purchase..... question about terminology

#19 Post by JasonE » Thu Oct 15, 2015 3:34 pm

ogopogo wrote:
So this is what I'm looking at - not too sure how to judge it. The plane is in O-M. If you search around you'll find it.
O-M? I wouldn't recommend it for your first aircraft. Once you have a better understanding of the maintenance requirements...then maybe. But people want far too much money for O-M planes. I wouldn't pay more than half of full value of a certified aircraft for an O-M one. The reason I bought my plane was to be able to fly places. O-M limits you staying within Canada. So much more to see!
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