450 smoh in 15 years

[OntheNumbers]

Hi,

I've found a C-172 I like with a low time engine, but it's over a 15 year span. I know that's a long time for such a low number of hours and I will be checking the logs very closely for the usual stuff and also for the longest gaps in usage over that time. The owner tells me she has flown the plane regularly over the time she's had the plane, once or twice a month but just the around-the-patch kind of stuff.

The owner also says it doesn't burn oil and the compressions are all good - but I discount that information. My plan would be to have the jugs pulled as part of the ppi and take a god look for corrosion.

Here's my question - what is the longest gap of time between flights in the log beyond which the likelihood of corrosion is just too high to even bother proceeding with the check? Or is it not even worth bothering with?

Aside from the engine, everything else looks pretty good.

Edit: the engine has 450 hours smoh in 15 years

Thanks

OTN

[c170b53]

You know, you just don't know and that's why you'll have to pull a cylinder and take a look inside to have an idea. If you really concerned have it pulled apart, inspected, repaired if required and continue the time.

[Colonel Sanders]

You need to get an eyeball on the cam lobes and lifter faces.

There's a quick and easy way to do that, without pulling jugs.

Also, remove the oil filter (or pressure screen if it doesn't
have one) and cut it open to look for metal.

[OntheNumbers]

Thanks for the replies. I guess worst case the engine will be badly corroded, best case it will be like a new engine with 450 hours on it. In the worst case, is the remedy an overhaul or is there something less costly that can be done. I'm not trying to cheap out, just trying to learn about the situation.

I don't know the simple way to inspect the cam lobes and lifter faces but my research tells me this would be a 6-8 hour job for an AME.

It is what it is, I guess

Thanks again.

[Colonel Sanders]

Money well spent! If the lobes and lifters are spalling,
the price of the aircraft just went down. A long way.

http://www.sacskyranch.com/eng61.htm

[CpnCrunch]

To be honest, 450hrs in 15 years isn't too bad...most private planes are a lot worse. Also if it has flown a few times a month that's pretty good compared to most private planes (the majority of which sit for MONTHS doing nothing). I would imagine the engine is in pretty good shape after only 15 years if compressions are good. However you do still need to do a thorough PPI.

The owner may not want you to go removing cylinders, and it may be overkill. Generally a compression check , boroscope and perhaps oil filter check are sufficient.

[OntheNumbers]

Well on average it's had 2.5 hours per month based on 450 hours in 180 months. That doesn't sound too bad to me either provided the engine has been run at regular intervals without any "long" gaps. But my original question was - what would be considered a "long" gap? The logbook awaits...

Thanks

OTN

[Big Pistons Forever]

Well on average it's had 2.5 hours per month based on 450 hours in 180 months. That doesn't sound too bad to me either provided the engine has been run at regular intervals without any "long" gaps. But my original question was - what would be considered a "long" gap? The logbook awaits...

Thanks

OTN

We put less than 40 hours on my little Grumman AA1 last year but the longest interval between flights was 10 days. A log book with gaps of 30 or more days between flights more than maybe once or twice in the last few years should send up the red flags. However pulling a jug will give you a very good idea of the condition of the engine. If the aircraft is otherwise in good shape and reasonably priced it is well worth paying the shop time to pull a jug as part of the prebuy inspection. If the cam and lifters are hooped you are looking at a 7 to 10 K repair bill by the time the dust settles. If the cylinders also have deep corrosion pits you are now nearly in overhaul territory (15 +K) on what you are going to spend on your "low time" engine to make it airworthy.

[AirFrame]

http://www.sacskyranch.com/eng61.htm

Colonel, this describes looking at the stuff under the rocker covers... But I thought you said that you could inspect the cam lobes without removing the cylinders... Did I misunderstand? If not, do you have any links to websites describing how to do that?

[GyvAir]

I haven't kept very current on piston engine work, but I do recall pulling the valve covers, rockers and pushrods, then fishing the lifter/cam follower out so that the cam lobes are in view through the pushrod tubes. I don't believe this is possible on all engine models though.

[iflyforpie]

I haven't kept very current on piston engine work, but I do recall pulling the valve covers, rockers and pushrods, then fishing the lifter/cam follower out so that the cam lobes are in view through the pushrod tubes. I don't believe this is possible on all engine models though.

The only engine that you can do this on the Cessna 172 is the H2AD. In fact, they designed the engine specifically so you could remove the lifter bodies without splitting the case. Every other 320 will let you take the lifters out, but the lifter bodies are stuck in there.

Ironically, it was the smaller lifter bodies that were the Achilles Heel of the H2AD. With less surface area, the surfaces were loaded more and contributed to this engine's terrible reputation of eating camshafts.

So yes, you will have to pull off two jugs to inspect the cam lobes and lifter bodies, which is about a day's work. CAR 625 APP C says you only need to do that if the engine has been out of service for 12 months. A better way might be to dump the oil and run a magnet through it and split open the filter (a bad cam will make metal show up in a new filter within five minutes) and use a bore scope for the cylinders.

450tt in 15 years is useless information without other qualifiers. If the plane lived in a dry climate, in a hangar, and was run for at least an hour every time it started, with preheat if necessary, and frequent oil changes regardless of hours, it would probably be one of the better engines out there.

I just finished inspecting an engine (IO-520-F) with 330 SMOH done in 1995 that had not been run in eight years! I bore scoped it, did a leakdown, put new oil and filters on it, new spark plugs, drained the old fuel and checked the sumps/screens, ran it for a while, checked the governor screen, then got a ferry permit and flew it to home base.

Pulled three jugs off and.... nothing. No rust in the cylinder barrels (plain steel), no corrosion on the pistons or cylinder heads, no rust spots on the cam, crank, or con rods, no pitting or spalling on the cam lobes or lifter bodies. Just some minor scoring of the cylinder walls and pistons (you could still see the hone and machine marks through them) and a bit of irregular wear on the cam... which is just about any engine out there with a few hundred hours. Oil filter came out clean.

I chalk it up to the dry climate it was in, the fact that it was hangared, that it had clean oil in it (not preservative--which would have been better), and that the owner didn't run it at all in the intervening time. The plane needs to fly, not just run.

[Colonel Sanders]

In my experience, the Lycomings have a much
bigger problem with internal corrosion from
lack of use, than the Continentals. Not really
sure why. Alloys used?

[OntheNumbers]

Well I have yet to see this plane, but the owner tells me oil was changed once a year due to low hours flown (a minus) and it has been hangared (a plus). But it's a west coast plane and it's a moist climate (another minus). Pie, sounds to me like your io520 lived in a dryer location, maybe in the interior where it's pretty arid. Amazing that it came through an 8 year dry spell so cleanly, though.

Can anyone pm me with a recommendation for an inspection facility in the lower mainland?

Cheers

[c170b53]

It can go either way; you may as IFFP suggests get away lucky. With a low time engine I'd take the conservative approach myself and have it torn down. If there's nothing wrong, you'll pay for bearings, rings, hardware and let the time continue. If there's more wrong then you won't mind paying for it in hindsight. Again just my conservative approach but maybe I'm too conservative for some or many. I know just the man for the engine work on the West Coast but it sounds like you need full maintenance support and whomever you choose may have their own favorite.

[Colonel Sanders]

Heh. You tear down that engine, I wager you're
out $20k by the time you are done, which is
money that you will never see again. It surely
will not increase the value of the aircraft that much!

[c170b53]

Last one cost me 5K with new mags but...you right it could go much much higher. That's why the unknowns often tip the decision to fold on a project and that's why there's plenty of carcasses out there.

[OntheNumbers]

Heh. You tear down that engine, I wager you're
out $20k by the time you are done, which is
money that you will never see again. It surely
will not increase the value of the aircraft that much!

You guys are scaring me

[Colonel Sanders]

Sorry. Tough love. There really is no such thing
as a good, cheap airplane. It's an urban legend.

I remember around 20 years ago, a really nice guy
whacked the prop on his 182. Off it came, out to
the prop shop. And so did the engine, which was
around 1000 TTSN for an inexpensive teardown
and inspection. Or so he was told.

Tens of thousands of dollars later, he had to sell
the airplane to pay for a new prop and an engine
overhaul.

Anyways, you do what you want, but I would do
an inspection for internal corrosion before I bought
this aircraft. The problem with the cam lobes and
lifters is so bad on infrequently flown private aircraft,
Lycoming has gone to roller lifters.

Do keep in mind that from a calendar standpoint,
this 15 year engine is past TBO, according to Lycoming.

[CpnCrunch]

Or go for a plane with a Continental (older 172, 182, 150). As Colonel says, in theory they tend to have more corrosion problems with the cylinders and less problems in the bottom end, which is much easier to check in a pre-purchase.

[iflyforpie]

The Colonel speaks the truth.

It is a quirky world we live in in aviation. If we don't see a defect, it is okay, but as soon as we see it, we must repair it.

I remember years ago we were doing a rush phase check on a Convair 580 to get it ready for a flight that night. Only one wing was supposed to be inspected, but during a coffee break they moved the aircraft out to get another plane out then put it back in 180 degrees. A coworker of mine found a crack--but it was on the wrong wing! After the mistake was realized, the management was screaming that they couldn't have this plane tonight because they would have to fix the crack!

Engines, same deal. They can go on forever but if you ever have to send a jug out or have the case split, everything inside needs to be free of corrosion and withing service limits. I had a 182 with a mid time engine prop strike... same deal. I had an older 172 with an O-300 where a valve got stuck (hadn't run in three years) and they had to toss the jug. Every other jug will have to be tossed as well if problems come up, turning a $300 valve job into a $1000 new cylinder kit... potentially x 6... plus labour and downtime.

[OntheNumbers]

Hey Colonel

I will definitely get the cylinder pulled to have a look-see. The whole rest of the plane looks very well taken care of based on the photos and my talking to the owner. But based on my read of this thread, a bad engine could/should veto the whole deal or cause the price to drop to compensate. The fact that the engine is already past it's tbo because of elapsed time is something I hadnt considered.

Thanks for all the discussion!

[OntheNumbers]

Just got word from the AME that there is corrosion visible in the cylinders with the borescope. Apparently they can't tell whether there is pitting or whether it's just surface corrosion that could be taken out by an engine specialist. Next step - pull one or two cylinders for a closer look.

[Colonel Sanders]

there is corrosion visible in the cylinders with the borescope

Get an eyeball on the cam lobes and lifter faces! I will wager they are
similarly pitted.

As to the cylinder wall corrosion - not very surprising, given that they are
nitrided - what were the leakdown numbers?

If the corrosion is very light, you might be able to get rid of it by running
the engine hard for a few hours, but frankly I am doubtful. It will require
honing at the least (with a new set of rings), and possibly boring oversize
with oversize pistons and rings. Even that might not do it. You might need
new cylinders.

On that subject ... don't "baby" an engine with low power settings. It
does not hurt it to produce rated torque at rated RPM as long as all
the temps (oil, CHT, EGT) are kept well within limits.

What kills an engine:

- internal corrosion from lack of use (eg most private aircraft)
- cold starts with inadequate pre-heat (Canadian winters)
- over-temping the metal

I run my Lycomings hard and often, and carefully keep the temps
'way down from the redline, and they have the best compressions
on the field.

[OntheNumbers]

One final question - I understand that corrosion on the cylinder walls, camshaft and lifter faces is a bad thing, but can someone please say what the consequences can be? I'd like to understand what a failure would look like - besides the obvious which I assume is an engine failure.

Thanks


OTN

[Beefitarian]

Intake cam lobes can slowly disappear overtime resulting in a significant loss of power that may not even be noticed. I don't know if it's the same for exhaust lobes. I have heard of people replacing automotive cam shafts where the lobe was completely round and therefore not opening the valve at all.