Aircraft Engine Wear

[Colonel]

Aircraft engines are hideously expensive. When you go to buy a private aircraft,
how do you know if the engine is ok? And, how can you take care of your aircraft
engine, so that it is reliable and strong, and doesn't prematurely fail on you?

People look at hours since major, and that's probably the least important factor,
and in fact a very low number is generally very bad.

Years since major overhaul is probably a more interesting metric. In commercial
use, for TBO calculations engine manufacturers assign hours per month regardless
if they are flown or not, so by 12 years (or so) your engine is actually "beyond TBO"
regardless of the hours on the tach.

Note that TBO has no meaning for a private aircraft, regardless of what anyone
tells you. I'm interested in years since major overhaul. If it's 20 or 30 years, it's
core value only. If it has 5 years since major, it would be nice to see 500 hours
on it. An engine flown 100 hours per year is generally in pretty good shape.

If it's 10 years since major with 10 or 20 hours SMOH, it's time to take it apart
and major it again. It's probably going to be a mess inside, from corrosion and
deposits gumming everything up (see AvBlend).

So. What is wears out an aircraft engine?

1) internal corrosion. This is the killer of especially Lycomings, who's cam lobes
and lifters and cylinder walls are terribly vulnerable to corrosion from disuse. You
probably don't fly every day, and if you live someplace warm, humid and salty, your
engine isn't going to survive very long.

People like to jabber on about borescopes and bullshit, but I have found you can
learn a lot about an engine by popping a valve cover.



If it looks like that Lycoming 540 that sat for a year, it's garbage inside and will
soon be making metal. Lycoming went to roller lifters which should help their
cam lobes, but remember you have to change them at overhaul, so that just got
more expensive.


2) excessive high temperature. The hotter you run metal, the shorter it's life. You
want to keep your CHTs under 400F and your oil temp under 200F. If you are
seeing higher numbers, you are shortening your engine's life. But remember to
keep the CHT above 300F as well, to keep the lead gaseous out the exhaust
port. Colder is not always better, ok?


3) excessive low temperature. Cold starts. A problem for you, not me. People
struggle with a start because the fuel won't evaporate, but that's the least of their
problems. For winter ops, you need multi-viscosity oil - NOT straight grade - so
it flows when it's cold. But even that has it's limits. As an engine gets colder,
the differential contraction of the dissimilar metals means that your clearances
go to zero. You can hang on the prop in the Arctic. This will destroy your bearings
after start. You must preheat when clearances are too tight. Similarly, after start,
you must sit and idle like a radial engine at minimum RPM to allow the cylinder
to heat up. If you hammer the RPM after start, the aluminum piston/pins will
expand faster than the steel cylinder, and will scuff and make metal in your oil.

Every engine is different, but my recipe for a cold start - which for me is 60F -
for a Lycoming is six seconds of prime at full throttle and rich mixture, after I
see six GPH on the flow meter. Then mags off and pull it through six cylinders,
so there is fuel in every cylinder and absolutely no chance of hydraulic locking
due to incompressible fluid in the cylinders, which will bend a connecting rod.

Then, I leisurely strap on my parachute and climb in and fasten all the fucking
buckles. No hurry, and I move slower in the cold, because 100LL takes a long
time to evaporate - the colder, the slower it evaporates - and liquid 100LL does
not burn - only after it slowly evaporates. So, take your time. Mogas in the
winter is awesome, if you can run it (I can't).

If I do this, I get a perfect start every time I crank, and RPM immediately down
below 1000 RPM, check the oil pressure climbing, mixture back an inch and
alternator field on to charge the battery.

If you start only on the left magneto (eg Citabria, Decathlon, etc) don't forget
to turn the right mag on after start! If you don't have toggles or rotary switch
for your mags, and you have a fancy Bendix twisty combined mag/starter switch,
it actually will do this for you, if you need it (right mag grounded while cranking).

I shouldn't mention this, but I know a Citabria owner who would use ether
(you know that starter stuff in a spray can) in the cold because 100LL wouldn't
evaporate worth shit. Horrified me, but it worked. He would get a start without
preheat, but I don't expect his bearings would last very long. You preheat for
engine clearance, not to fucking evaporate gasoline. No one understands this,
especially in the age of multi-grade oil, which has a pour point of -40F. Or -40C,
your choice. I only remember that temperature because that's what it was in
Cold Lake, the day I was born.


Anyways. Fly your private aircraft as often as you can. Be aware of the dangers
of heat, humidity and salt in the air. Run straight grade in the summer, and
multi-grade in the winter (if you have real winter). Keep the CHT below 400F
and above 300F. Keep the oil temp below 200F and if you are running straight
grade (W100 or W120) I strongly recommend at least oil temp 90F before takeoff.

Preheat in the winter. Not only your engine, but your cockpit, for many reasons.

And I simply cannot recommend strongly enough: Camguard and a Battery Tender.

Like Top Gate, I know I'm kind of a broken record, but Camguard with cheap oil
is the best oil that money can buy. And a Battery Tender ($30 on Amazon) keeps
your battery strong, extends it's life, and stops it from freezing and cracking and
peeing destructive battery acid all over your aircraft - I've seen that many times
before.

If you can't be bothered to put a Battery Tender on - or you don't have power
(I have seen solar power for them) please take your battery out of your aircraft
in the winter and take it home with you. It will do less damage and live longer
and maybe you could even charge it there. Remember that whenever a lead
acid battery drops below 12.8V it starts to sulfate the plates and it's life is
shortened. Ever wonder why some people can get 10 years out of a battery,
and other people are replacing them every year?

Remember that there is nothing special about airplanes. The same applies
to cars, motorcycles, boats, etc. I have more motorcycles than any sane person
would ever need, and they sit with a row of Battery Tenders on power bars on
the wall, all plugged in all the time with solid green lights.



Whenever you shut it down, plug it in. You may not plan it, but it may be months
before that engine runs again.

Pessimists live longer. Sorry about that, but it's true.

-- EDIT --

Next subject: hydraulic locking. You may think it's only something that radial engines
suffer from (engine oil in bottom cylinders) but that's not true. There is a back of an
envelope near me which will soon be scribbled on.

[Nark]

Thanks Col.

I've heeded this advice in the frozen northern plains of the midwest. (prairies for you even more northern folks.)

It baffles me that the flight school 172's can start up, run-up and take off, all before my oil temp reaches 20C (I religiously preheat, and low idle starts). Then again, why do they give a shit when they go in for 100hr's 5-6 times a year, and at overhaul time, they come up for sale?
How much metal do you think that oil is circulating?

My club 182 I beat in to the guys to get the oil nice and warm before adding power for a run-up. Seems to work for now. It's on trade-a-plane right now, for roughly 250% of what I paid for it. Lets see what comes of that.

Happy Thanksgiving you transplanted Canuck.

[Colonel]

Happy Thanksgiving you transplanted Canuck.

You too! The wife and I are making Turkey, garlic mashed potatoes, gravy,
carrots and lemon meringue pie using lemons from a tree in my back yard.

Being from up north, I really don't get all the fruit trees. Rats gotta eat something,
I guess. And my basset hound got the shits and I couldn't figure out why, until I
saw her in the back yard on her hind legs, eating plums off the tree.

PS With multi-grade oil (cat piss) you don't actually worry about it flowing at
low temps. Not a problem. What I look for is 200F on all CHTs before I advance
the throttle to 1700 RPM for a runup. That tells me what I need to know, about
the clearance in the rapidly-heating piston/cylinder. Oil temp is an indirect proxy
for the CHT - it's warmed as it passes through the heads. If your oil is warm, that
means that your cylinder heads are, too. Note that your cylinder heads are aluminum
and conduct heat very well, and are screwed onto the steel cylinders which is
where the trouble will be (with the aluminum piston).

It's on trade-a-plane right now, for roughly 250% of what I paid for it

Fuck me.

[TwinOtterFan]

Last winter (my first winter flying) I used to be one of the first guys walking out to my plane and mid to late pack taxiing. Figured I just sucked, but realized later I was one of few that actually added oil when it was low, washed the windows and called for de-icing if needed. Also waited for proper Temps.

I think that is why I hated Toronto/Brampton so much, everyone is just in a huge rush. Like the Colonel said, start the plane. Then just sort out some stuff. Seats, belts, maps, iPad, radio freqs.

[TwinOtterFan]

Just seen this posted,

Screenshot_20211125-112843_Instagram.jpg

[Colonel]

Hey, that's cool.

And, you don't have to take care of the equipment, if you don't mind it failing
sooner and at inopportune moments.

However, I fuss over my engines. Comes in handy, single engine over water.
This is across the Gulf of Mexico in an S-2C. I think Havana gave me an IFR
clearance, right before my portable Garmin GPS (only Nav) kicked offline. Sigh.



The good news is that North America is a pretty big target. After the layer
thickened up (ahead of a cold front) I bombed down through a hole and flew
at 500 AGL to Key West.

For some odd reason, I derive pleasure from having to climb to pattern altitude
when I arrive at an airport. The visibility is generally pretty good underneath,
and you can see the cruise ships in time to weave around them. It's terribly
tempting to do a roll overhead one from the surface, but if some goddamned
tourist got a photo of me smiling inverted over the ship, there would be hell
to pay.



Me in the yellow Pitts. Freddy always made me take the tailwind for the head-on takeoffs.



That's me and my kid doing a head-on takeoff at our old home airport. The radio
call always confused the transient pilots. "Pitts formation, taking off on runways
24 and 06". I didn't think it was that complicated.

In retrospect, I could never figure out why Canadians hated that kind of flying so much.

It's an awful lot of fun.

[Colonel]

Almost forgot:

lemon meringue pie using lemons from a tree in my back yard

It's a lot of work - not like a raspberry or blueberry pie (pro tip - cook the blueberries
first). Making a lemon meringue pie from scratch is about the same as a cylinder
R&R, assuming that you can get someone else to take off (and put on) all the cowls
and baffles and intake and exhaust and all that junk.

Moral Of The Story: If you're going to fly, you'd better learn to fix them, too. And
if you're going to eat, you better learn to cook, too.

I honestly don't know how anyone goes through life without knowing how to fix
their motorcycles or make food. YouTube videos, people! It's not that hard.



-- EDIT --

Thinking about this, I know a young guy - mid 30's? - with a Desert Eagle. Has never
cleaned it. I am not making this up.



Me spending quality time with the Dan Wesson after a visit to the range.

Next week: bleeding hydraulic lifters for the dry clearance tappet check.

[Big Pistons Forever]

4 cylinder Lycomings are almost indestructible, if and this is a huge if, They get regular use. The flight school at my home drome runs their Cessna’s 3500 hours before overhaul. Those hours include much student abuse, but they don’t seem to care. However the airplanes are doing almost 100 hours a month on average and that is why they do so well

Most private airplanes don’t do a 100 hours a year and that is why they suffer the engine killing corrosion that results in the early overhaul.

Got a typical 4 banger in your private airplane ? Good then there is only 2 things you need to do for it to have a long and happy life

1) change the oil every 6 months and,

2) Fly it for at least 30 minutes at least every 2 weeks

Unfortunately the bad habits that you can get away with in your training C 172, don’t transfer to the bigger engines, particularly turbo charged Continentals. For those engines proper warm up, smooth and slow throttle movement, proper leaning technique, and CHT management; are not optional anymore.

For example the Continental Motors engine operation manual for the GTSIO 520 has a note that applying takeoff power before the oil and CHT’s are in the operating range will subtract approximately 50 hours of engine life per occurrence.

When teaching in the C172 I tried to inculcate good engine operating practices but I think I was a bit of an outlier in the school.

[Colonel]

Yup. Lycoming cylinder heads are amazing, the abuse they happily take.

However, the Lycoming cam/lifters/cylinder walls will NOT forgive you, if
you let them sit (and corrode internally). Personally, I have found that running
straight grade oil and at least 5% (I prefer 10%) Camguard makes a HUGE
difference - it really slows down the internal corrosion of an infrequently
flown Lycoming. You can actually smell a 10% concentration on final, with
the throttle back. Yum!

Continental cylinder heads are much more delicate wrt thermal. Probably
the best piece of advice I can give, is to lean in the descent. People will
tell you "an inch of MP per minute" decrease, and that's silly. I have flown
TCM for half a century, and they are perfectly happy with changes of 5 inches
of MP - if you lean in the descent. You don't take off with an "inch a
minute of MP" increase, do you?

You can actually land a TCM single (or twin) with the props and mixtures
back, but people don't like to do that. Advance them as late as possible
on final, after gear check. If the props go forward and the RPM goes up,
you have advanced them too early. You want them on the pitch stops, first.
Similarly with the mixtures, you want to be at a low enough power setting
that the fuel flow doesn't change when the mixtures go forward. No damage,
that way.


If you know you're not going to fly this winter, you could do a lot worse than
draining your oil and adding W120 and 10% camguard and running it up, then
parking it. Not only stops the internal corrosion, it reduces the valve sticking
that you get when you park an engine too long. Pull the battery, take it home,
top up with distilled water and leave it on a tender all winter.


If you're going to fly this winter (and be honest, ok?):

1) drain the oil, add multi-grade and a new filter if you are unfortunate enough
to have one. I prefer Shell over the "cat piss" blue bottle, when it comes time
to choosing multi-grade oil. You must use an aviation (ashless dispersant)
multi-grade oil for cold wx ops.

2) add at least 5% Camguard. At this point, the expensive additives in the
Shell 15W50 are a waste, so the cheap cat piss gets more tempting.

3) preheat! And remember, never fly below the pour point temp of your oil,
to avoid congealing in the oil cooler (not good).

4) consider a winter kit, which has restrictor plates for the oil cooler and
cowl air intake. Flying with really cold oil temps does not boil the water
out of the crankcase very quickly. Aim for at least 150F oil temp. And
take the winter kit off in the spring, ok?

5) don't look at your EGT's after takeoff.

6) lean the mixture in the descent, and keep some RPM on. Don't stop
the prop on final, ok?

7) battery tender, or remove the battery every flight. Your choice. Don't
let it freeze and crack and piss corrosive battery acid all over your airplane.

8) with multi-vis oil, oil temp before takeoff doesn't matter very much, as
compared to straight grade. Minimum RPM after start for at least a minute.
Wait for the oil pressure. Ensure that you have 200F on the CHT before you
runup, to keep your cylinders happy. After the runup, you should be good to
go. Remember that the runup heats up the cylinder heads, and the oil circulates
through them, and should start to warm up the oil noticeably. Oil warms up
very slowly with cold cylinder heads (a concern for old fashioned straight grade).

9) after landing, when your oil temp is hot - it will actually get hottest after
landing, and you taxi in - if possible, after the props stop and you get out, open
the oil access hatch and remove the filler cap (TCM) or prop open the dipstick
tube (Lycoming) to create a convective chimney at the top of the crankcase, to
vent the evaporated moisture out of your engine. Which is kind of the whole
point of the flight - get rid of the water inside your engine!

10) Try not to think of the irony of taking cold wx ops advice from someone
who's idea of winter is this:

[digits]

Is camguard useful in Continental engines as well?