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Aircraft Engines

Flienlow

Registered User
I have a few questions about aircraft engines.
When evaluating a plane How do you calculate the engine? Do you simply divide the time remaining on an Engine TBO vs cost of a new one? In other words if a new engine was 35k and had 2000hr TBO that engine is worth around 17.5/hr. It seems one can then work the math up or down for value?

Also, When an Engine hits TBO. Does that mean the entire engine needs to be rebuilt? Do you break it down and inspect and replace as necessary? Just buy a new damn engine cause ya "Might as well..??"

Sorry if these are stupid questions. Plane-anomics is very difficult for me to figure out.
 
I have a few questions about aircraft engines.
When evaluating a plane How do you calculate the engine? Do you simply divide the time remaining on an Engine TBO vs cost of a new one? In other words if a new engine was 35k and had 2000hr TBO that engine is worth around 17.5/hr. It seems one can then work the math up or down for value?

Also, When an Engine hits TBO. Does that mean the entire engine needs to be rebuilt? Do you break it down and inspect and replace as necessary? Just buy a new damn engine cause ya "Might as well..??"

Sorry if these are stupid questions. Plane-anomics is very difficult for me to figure out.

Its a total crapshoot.

Calendar time since overhaul means just as much, if not more than hours operated since overhaul.

Where are you located at? If this is your first rodeo you might want to hire somebody to evaluate what you are looking it.

Tim
 
Everything you read is subjective and your airplane journey will be subjective, too. The only truth an experienced aircraft owner can offer a new guy? Bring money. Nobody expects a $40K annual but it happens. Not always and never when you're prepared for it, but that's the reality of airplane ownership.
 
For a personal aircraft TBO means little, if it is running fine just keep flying. When it does come time for a rebuild case, crank, rods can be inspected and reused. Cylinders can be rebuilt but usually better to just get new. Overhaul Mags, carb, replace other parts as needed.
DENNY
 
I have heard of flight schools operating O-320s over 3,000 hours before the overhaul.

I also heard of a pair of engines making less than 20 hours from factory new to junk, (pilot induced disaster there).

Normally aspirated Lycomings have a great reputation of dependable until condition warrants overhaul, except the H2ADs which were a disaster. Continentals seem to be a bit more temperamental, (O-470U was another problem child), but with just a little love they operate great, and will take sitting better than Lycoming without cam corrosion.

An engine that gets flown every few days or week for an hour or so seems to last better than one that sits. Some planes you can see quite a bit of the internal workings with a bore scope, others you need to pull cylinders to look inside.

Who overhauled the engine also may effect the value, and to what tolerances. Overhaul tolerances are different than 'Remanufactured,' Not everyone pays to have the case machined and line bored at overhaul, among other things... sometimes it does not matter- other times it might!

If you find a really nice plane you like, it is often worth pulling the cylinders to see the internal parts of the engine if you can not bore scope the cam. But as said earlier, have a good mechanic take a look for you when it is time.

AS far as costs, remember that the price of the engine is only part, you need to remember shipping, removal and installation, prop and accessories if not included.

Lots to learn, and this group keeps teaching me things every week!
 
Everything Aktango said is correct. I just had to pull an engine that was running perfectly. Went in for annual, had burned exhaust valve. Pulled cylinder, and the cam and some lifters were spalled. Unexpected OH. It happens...and that engine had been run over 200 hours in the past year, had no symptoms, and all oil changes/filter cuts were perfect. Stuff happens
 
For a personal aircraft TBO means little, if it is running fine just keep flying.
DENNY


Ok, now I am even more confused. I thought at TBO the engine NEEDED to be rebuilt or replaced? And the comment about the flight schools running into the 3000hr mark?? Does this mean at TBO you can test the compression, replace the plugs and if all is well keep going?
 
in fairness, there is some disagreement on how to proceed at TBO. For part 91....emphasis...part 91....there is no mandate to overhaul at a particular "hours in service", nor "calendar years in service". (the engine manufacturers have a calendar time recommendation on overhaul, as well as hours in service).


Many of us monitor engine health via checking oil samples (I don't), cutting oil filters (I do), compression checks and borescopes (I do these more than annually...but I fly more than average), and "on condition" inspections (I do). I've had engines go well beyond TBO, and engines pulled due to problems.

(my opinion....you should keep financial resources available for overhaul because you never know when.....)

My neighbor has a Lycoming IO-360 that has 3600 hours on it, going strong....and I just pulled an O-470 with 1400 hours on it, due to cam/lifter spalling.


YMMV
 
General rundown on engine maintenance, assuming it's on a personally operated aircraft (Part 91): You're not legally required to overhaul engine at TBO. You ARE required to perform any required inspections called out in Part 43 at each and every annual inspection (every 12 calendar months). As noted in posts above, items such as compression, oil pressure, and filter/screen 'discoveries' will drive decisions on whether to open up an engine, whether at TBO or not.

Are your questions concerning an aircraft you own or are you looking to buy? Either case, find a trusted mechanic and let him evaluate the engine. If it's already 'yours', fly it until you have reason to remove the engine from service. As the cylinders wear, you will see compression tests results fall at each inspection and usually a corresponding decrease in power. As internal components wear, such as oil pump gears and rod and main bearings, you'll start to see a reduction in oil pressure, especially at operating temps. Your mechanic may find metal in the filter or screen at oil changes, indicating cam, lifter, or bearing failure. These are issues that can't be argued with. When found or when not meeting specs, the engine must be repaired. If it requires removing all cylinders or splitting the crankcase, many times a complete overhaul will be as or more economical than just repairing, especially with high time engines. Red flags with an engine you wish to buy is one that has sat for more than a season or so (considering local environment) or one that has extremely low time since overhaul, i.e. selling the aircraft and the engine has 3 hrs since overhaul.

Keep in mind that service bulletins and service letters are not mandatory for part 91 operations. However any and all applicable ADs are absolutely, 100% mandatory, no matter what. So if there is an AD on an internal engine component, it can drive the decision to do an overhaul at the same time.

So sit down with your mechanic and get his view of the engine condition. Use his input to make your decision on when to do the overhaul. At some moment in time, you, as the operator, may just decide that it's time for the full overhaul. Time, increased maintenance, reduced performance, etc. will add up for you and you'll wave the magic checkbook and declare 'It's time'.

Web
 
Are your questions concerning an aircraft you own or are you looking to buy?

This would be my first Aircraft. I am trying to sort all this out so when I do get the Mechanic involved I am not wasting both of our times. Especially since a lot of planes ( most in fact ) are remote. I also don't want to buy something and then go "Honey... About the Plane... Ya see, there's this thing called an AD and its gonna be bout 40k to fix." -I'd get dropped like a downer cow on that one for sure.
I personally know of a Golden Eagle that went into Annual and came out of it $150,000 later with a new engine, Turbo, exhaust manifolds, and half the tail ripped apart for an AD. And that was in 2005. - Hence, I want to educate myself the best I can before I buy a plane.
 
The mechanic's job is maintenance. He'll have more insight into these issues as a technician than you'll have as an operator. Get him involved now.

Web
 
One think that I try to stress to everyone is Find the IA that will be doing the annual before you even start looking at any plane!!! Not an A&P, friend, or guy that owns 12 planes. They may be able to give great advice but they will not be signing off the annual inspection and what is good for one IA may cost you twenty grand with another!! From an engine standpoint you are not going to be able to understand all the issues that could be pitfalls or issues from the internet. You could even go to school for a year and still only have a basic understanding. Soooo go find a good IA and start talking with him/her about what your mission/goals are and go from there. I looked at planes for 6 mo before my IA approved of the first one. Do not fall in love until the IA approves of the affair and tells you how much it will cost!!!
DENNY
 
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One think that I try to stress to everyone is Find the IA that will be doing the annual before you even start looking at any plane!!! Not an A&P, friend, or guy that owns 12 planes. They may be able to give great advice but they will not be signing off the annual inspection and what is good for one IA may cost you twenty grand with another!! From an engine standpoint you are not going to be able to understand all the issues that could be pitfalls or issues from the internet. You could even go to school for a year and still only have a basic understanding. Soooo go find a good IA and start talking with him/her about what your mission/goals are and go from there. I looked at planes for 6 mo before my IA approved of the first one. Do not fall in love until the IA approves of the affair has tells you how much it will cost!!!
DENNY

Ditto Denny
 
If you are buying an airplane and it is your first ownership experience, there is a lot to learn. If it is for your personal non-commercial use, then the TBO recommended by manufacturers do not specifically trigger any automatic action on your part.

However, if there is an AD pertaining to time since overhaul, then that become mandatory (not sure if there are engines with that circumstance in the general fleet, but Beaver engines have some limits on kinds of maintenance that can be done depending on how long since overhaul).

You will find there are lots of examples of airplanes that fly engines well beyond TBO. For your planning purposes, you should assume that those are other people's engines, and not your own. The reason for that is that the chance of an engine flying well past TBO while maintaining legal airworthiness is increased by frequent use, such as flight school airplanes. Most airplanes for sale are privately owned and do not fly enough to have a realistic shot at getting those same types of hours, and extended sitting between flights makes it less likely that the engine will last that long.

The reverse is in fact true, an aircraft with an apparently low time engine might have sat long enough at different times that the actual engine condition is not as good as that low number suggests.

My personal preference is to buy an airplane that has a high time engine, run it on condition until it needs overhauled, and then overhaul it. That way both the seller and I have a common understanding that the engine is basically timed out for value purposes and we don't have to argue over whether it has a bunch of retained value. However, the reality is if you are doing that then you are expecting a $20K bill at any time. If that is not feasible or can't pass muster with the finance officer in the house, then you are better off buying an airplane with a recently overhauled engine and paying more to do so up front. The recent overhaul should be recent in terms of both time and hours. And you really should do some investigating into what sort of shop did the overhaul. Buying such an airplane, if you get a good engine, will save you money in the long run, but most people don't sell an aircraft right after they pony up for an overhaul, so it may involve some careful shopping.
 
Finding a good mechanic before you buy will save you $$ in the long run. Some mechanics have certain aircraft that they refuse to work on, and often for great reason. Some mechanics love rag wings, others don't know anything about fabric... might make a difference for you.

my mechanic tells me to anticipate 10% of the aircraft value for maintaining it each year. Some years you get buy for cheap, others you do a top end, (replace all cylinders- sort of a half overhaul).

As much as we talk about condition of the aircraft, the paperwork is a place that can cost you big dollars in a hurry. If modifications or ADs have not been signed off properly, then your mechanic has to go through and recreate or re-do them, sometimes buying expensive paperwork on things you think you have when buying the plane... These are the things a mechanic should find for you in a Pre-Purchase inspection.

As an example, my Maule, (current plane) was advertised as engine having 700 hour Since Major Overhaul. As the AI was going through the logs he was reading the engine documentation, and notices that the engine shop had an 'OVERHAUL' sheet signed, but in the sign-off the words were changed to 'Prop Strike Inspection', IRAN, (Inspect and Repair As Necessary).

The aircraft and engine had about 1,100 hours total time, and because of the way it was signed off, and later confirmed with the engine shop as only a prop strike inspection, the engine legally had 1,100 time since overhaul. The bottom end had gotten the equivalent of an overhaul, (new cam, lifters, bearings and such), but to same money they did nothing to the top end.

For me, flying private, I will change out the cylinders and pistons when they need to be replaced, but expect the engine to run well beyond 'TBO' as the bottom end is actually newer.

Yes, I did get a price adjustment for the time issue.

Moral of the story: a quality mechanic can save you BIG dollars, just like a borderline one will cost you. No percentage in going cheap on mechanics!
 
He has his detractors, and deserves them, but Mike Busch’s Engines book would be worthwhile reading.
 
One think that I try to stress to everyone is Find the IA that will be doing the annual before you even start looking at any plane!!! Not an A&P, friend, or guy that owns 12 planes. They may be able to give great advice but they will not be signing off the annual inspection and what is good for one IA may cost you twenty grand with another!! From an engine standpoint you are not going to be able to understand all the issues that could be pitfalls or issues from the internet. You could even go to school for a year and still only have a basic understanding. Soooo go find a good IA and start talking with him/her about what your mission/goals are and go from there. I looked at planes for 6 mo before my IA approved of the first one. Do not fall in love until the IA approves of the affair and tells you how much it will cost!!!
DENNY

Disagree. Just because a guy holds an IA cert doesn't mean anything.


Tim
 
The price of an engine is almost a given. The fabric, paint and the airframe under the fabric can easily exceed the price of the engine.
The most important thing to look at is everything.
I agree, a bunch of letters after a guys name doesn't mean he knows anything.
 
As SB pointed out, there's always the crapshoot aspect: there may be things not observed from a regular inspection that cause problems, there may be issues apparent on even a superficial inspection that never cause problems, or there may be enough problems to justify an immediate overhaul by a well-known builder, only to have the engine fail on the 10th hour after rebuild....as happened twice to my BIL (maybe it's him, not the engine ;-) )

FWIW,

- There's more to the aircraft than the engine: depending on the type of craft, the engine probably represents the biggest exposure to $$ and also the most variable as far as $$ (and safety?) risk goes.....but you also don't want a great engine pulling a hunk-a-junk through the air with the wings about to fall off.
- In a different field, I have more than a few letters after my name...and I'm always concerned about how little I know, so the mere fact that someone has a designation doesn't mean that they always know.....although having the letters can't hurt, IMO.
- ....however, one can't go wrong, IMO, in finding an experienced local mechanic, at least A&P if not IA, that is knowledgeable about the type of craft to be purchased and is trustworthy and then using that mechanic from day 1 to inspect the engine (and the rest of the craft), perform annuals, and do maintenance. There is, again IMO, very real benefits to having the same professional look at your aircraft from prior to purchase, to tweaking, to annual and so on. Circumstances dictated otherwise at odd occasions, but I always found that the more consistently the same mechanic looked at the ol PA-12, the fewer surprises, the more consistent (= good) the work, and the lower the $$, excepting only the truly "Oh, Sh**" stuff.
- How to find a good mechanic? Ask around, ask on this forum (probably via PM), ask the locals, look up on the local court system if they've been sued, etc.
 
Tim
I agree, AND THAT IS MY POINT!! The local IA may not have the experience to work on say a fabric aircraft and what to cut out fabric from each wing for testing yearly/send out gear bolts for testing yearly/or other nonsense, however, it is the IA (not A&P, buddy, or guy with 12 planes) that will sign the Annual!! So you have to find one that has the knowledge to work on the plane you are buying, BEFORE YOU BUY THE PLANE!!! Lots of post with guys having bought a plane with a good pre-buy by an A&P or IA only to have huge issues getting the plane approved at annual by local IA due to a lack of knowledge/local FSDO issue/paperwork/STC/or other modification. What one IA feels is a valid log book entry only event, can turn into a year of a grounded plane waiting for a field approval. It usually takes some time and luck to find a good one but from a money standpoint you will be way ahead. If it is a long distance buy you may have to arrange for pictures, log book information, phone calls to aircrafts last IA. Even with all of that or a hand on inspection it is still a bit of fly it and see what you get.
DENNY
 
Tim
I agree, AND THAT IS MY POINT!! The local IA may not have the experience to work on say a fabric aircraft and what to cut out fabric from each wing for testing yearly/send out gear bolts for testing yearly/or other nonsense, however, it is the IA (not A&P, buddy, or guy with 12 planes) that will sign the Annual!! So you have to find one that has the knowledge to work on the plane you are buying, BEFORE YOU BUY THE PLANE!!! Lots of post with guys having bought a plane with a good pre-buy by an A&P or IA only to have huge issues getting the plane approved at annual by local IA due to a lack of knowledge/local FSDO issue/paperwork/STC/or other modification. What one IA feels is a valid log book entry only event, can turn into a year of a grounded plane waiting for a field approval. It usually takes some time and luck to find a good one but from a money standpoint you will be way ahead. If it is a long distance buy you may have to arrange for pictures, log book information, phone calls to aircrafts last IA. Even with all of that or a hand on inspection it is still a bit of fly it and see what you get.
DENNY

Lots of great points Denny!

It is cheaper to just fly the mechanic (I/A) to the plane to inspect than to fly it home and go 'oh shoot!'.

But I don't fly the mechanic until logs have been inspected and I am ready to write the check. Then have the mechanic do the look at the plane, then send money.
 
IAs aren't fortune tellers. I've had a 900 hour TTSN engine break a rod. A factory reman fail at 30 hours. A different factory reman have the factory new crank recalled at 100 hours. Millennium cylinder AD. Titan cylinder AD. Factory Superior engine recalled and scrapped at 20 hours. Every one of these had no symptoms or issues that any IA would have caught. The 1200 hour motor I bought from a friend had a completely corroded cam. Couldn't have caught that, either. Airplane engines are a crapshoot.
 
Ok, now I am even more confused. I thought at TBO the engine NEEDED to be rebuilt or replaced? And the comment about the flight schools running into the 3000hr mark?? Does this mean at TBO you can test the compression, replace the plugs and if all is well keep going?

Good flight schools change their engines at TBO for insurance purposes and they are flying for hire. We have 50 airplanes at the school I work at, we change a lot of engines for condition and/or TBO. If you are just a recreational flyer, you are not required to change/overhaul the engine for airplanes flying under part 91 and not for hire. Based on that, a lot of people just do a top and inspect the cam through the cylinder base.

Oil analysis is another thing a person can do if they have a history to track wear, not perfect but it is another indicator of engine health. Seeps and leaks also point to how the engine is doing, case halves that have oil can be a detriment and cause for splitting the case. With that being said, there is a guy in Montana who flew his Lycoming 7000 hours, but that airplane was flying pipeline patrol for years. The owner told me that Lycoming bought his engine just to analyze it. They reported that the engine was still within serviceable limits.
 
….. Find the IA that will be doing the annual before you even start looking at any plane!!!..... Soooo go find a good IA and start talking with him/her about what your mission/goals are and go from there. I looked at planes for 6 mo before my IA approved of the first one. Do not fall in love until the IA approves of the affair and tells you how much it will cost!!!

There's IA's and then again there's IA's-- people's idea of a "good IA" differ.
I know one IA who expects everything to be perfect, I've seen him balk at stuff which is perfectly legal & airworthy, just not like new.
Perfect is great, except it tends to be pretty expensive.
Another one I knew loved to nitpick airplanes to show off to the owner just how smart he was--
he buffaloed a lot of people & cost several airplane owners by making mountains out of molehills.
He finally ended up doing something like that to a guy who was the airport manager,
it eventually resulted in him getting kicked off the private airport where he was based.
I've seen IA's who were hacks IMHO but had their customers buffaloed--
"he sure charged me a lot, he must have done a good job".
This kinda thing makes you really appreciate the good ones,
I'm lucky enough to know a couple.
 
IAs aren't fortune tellers. I've had a 900 hour TTSN engine break a rod. A factory reman fail at 30 hours. A different factory reman have the factory new crank recalled at 100 hours. Millennium cylinder AD. Titan cylinder AD. Factory Superior engine recalled and scrapped at 20 hours. Every one of these had no symptoms or issues that any IA would have caught. The 1200 hour motor I bought from a friend had a completely corroded cam. Couldn't have caught that, either. Airplane engines are a crapshoot.

You need more than a four leaf clover in your pocket you need a whole leprechaun. Seriously, I hope the new engine treats you well!
 
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