Engines that sit idle

AlleyCat67

AlleyCat67

Pre-takeoff checklist
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AleyCat67
Hi POA...

I'm looking at buying an AA5B (Tiger) that has sat essentially idle for several years. It was hangared in a dry climate (California), but there's certainly the potential for corrosion issues with the O-360. Part of me thinks I should just walk away. But... how effective would it be to have a cylinder pulled during pre-buy, and have the cam inspected for pitting? If that inspection turned out to be clean, would I have good reason to think that the engine would make TBO? Also, any ROM on the cost for that inspection during a pre-buy?

This is my first airplane purchase, and it's been pretty frustrating so far. It amazes me how many folks have let their planes sit around for months/years and then decide to sell. But I'm probably preaching to the choir on that...
 
The climate out side of the engine means nothing. All engines the have been run have water inside. it will normally seek the lowest part of the engine and set there under the oil. In some engine This does no harm, but in a flat engine that's the oil sump.

any two metal parts in contact will have Electrolysis occur between them. The time clock varies greatly, but it will eventually happen.
The big offender is the lifter to cam junction. very small pitted lifter will require a long time to eat away the cam lobe, deeply pitted one will do the job quickly.
So, when you pull a jug, you will see a very nice cam with a pitted lifter waiting to do its thing. When you replace the jug, and fly away the lifter goes to work. some time in the future you loose the cam.
Lycoming is famous for it.

My advice, unless you are ready to replace the engine now, don't buy it.
 
Even if the engine isn't rusted inside like Tom says, you're going to be on a rubber hunt. The carburator, the gascolator, and just about every hose is likely to be suspect.
 
It may be in excellent shape. You never know until you look. Corrosion happens but not every time. You could buy a 1000 hour regular flier and find corrosion on the cam. If you want a guarantee you'll need to buy new.
 
I'll add....if it were mine....you ain't pulling a jug just to look see.
 
Stewartb said:
It may be in excellent shape. You never know until you look. Corrosion happens but not every time. You could buy a 1000 hour regular flier and find corrosion on the cam. If you want a guarantee you'll need to buy new.
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Stewartb - Understood. My question was on the efficacy of a cam inspection as an indicator of incipient corrosion. For example, is it possible that the cam inspection would show no obvious corrosion, but then spalling or pitting would occur after another 100 hours? Obviously there are no guarantees but I'm just looking for some experience. As noted above right now the best answer is probably "walk away".
 
Probably not. What you see is what you get. I was taught that any irregularities on the cam that are detectable with a thumbnail are reason to tear down. If you see a cam that passes inspection and expect to fly it regularly and maintain it properly you have no reason to expect a problem.
 
If the rest of the airframe is what you want, price it as a runout. Change the oil and inspect the filter in 5, then 10 hours, then 15 hours. If you make it past 60 hours everything stays healthy, you won the lottery. If not, you got what you paid for.
If the cam spalls, the engine is toast but st not likely to catastrophically fail without warning.
Expect to oh the mags, hoses, harness, replace fuel pump etc in short order. I rolled the dice, and more than a couple hundred hours in, I'm a happy man.
 
AlleyCat67 said:
Stewartb - Understood. My question was on the efficacy of a cam inspection as an indicator of incipient corrosion. For example, is it possible that the cam inspection would show no obvious corrosion, but then spalling or pitting would occur after another 100 hours? Obviously there are no guarantees but I'm just looking for some experience. As noted above right now the best answer is probably "walk away".
Click to expand...
there are no guarantees.....and if it were to happen, you won't know for another 20-30 hrs of use.
 
AlleyCat67 said:
Hi POA...

I'm looking at buying an AA5B (Tiger) that has sat essentially idle for several years. ...
Click to expand...

If this is the orange one at FletchAir with 1400 hours sitting next to mine in pre-buy, they're doing an SB valve wobble test and results weren't promising ... the test of the plane appears to be in pretty good shape.
 
danhagan said:
If this is the orange one at FletchAir with 1400 hours sitting next to mine in pre-buy, they're doing an SB valve wobble test and results weren't promising ... the test of the plane appears to be in pretty good shape.
Click to expand...

Nope... it's N451CD at Cable Airport (it's on Controller)
 
danhagan said:
If this is the orange one at FletchAir with 1400 hours sitting next to mine in pre-buy, they're doing an SB valve wobble test and results weren't promising ... the test of the plane appears to be in pretty good shape.
Click to expand...
Dan,

Does this mean you've got an offer on your Tiger? Saw it listed on Barnstomers. Looked nice.
 
AlleyCat67 said:
Stewartb - Understood. My question was on the efficacy of a cam inspection as an indicator of incipient corrosion. For example, is it possible that the cam inspection would show no obvious corrosion, but then spalling or pitting would occur after another 100 hours? Obviously there are no guarantees but I'm just looking for some experience. As noted above right now the best answer is probably "walk away".
Click to expand...

This is a question I would love to know the answer to, also. My experience(s):

1. I bought a Tiger with a mid-time engine (O-360) that had sat unused for 5-6 years but had flown 20 hrs or so, in the 6 months prior to my purchase. This was in the dry Southwest. The pre-buy showed no metal in the oil filter when we cut it open and it turned out that I had no issues with that engine over the next few hundred hours then sold the aircraft.

2. I bought a Bellanca Scout(O-360) with 400 hrs total time since new. Aircraft was about 15 yrs old. It had sat unused for 2.5 yrs prior to my purchase, in southcentral Alaska. Pre-buy showed compressions all 77 or above(I know, that tells you nothing about the cam) and everything else looked great. We did not inspect the engine internally. Bought the airplane, flew it 100 hours that summer. At the first annual that September, my IA told me the oil screen was full of metal and the engine needed to be totally rebuilt. Expensive lesson.

My thoughts (I'm not an A&P): I believe a dry climate is a lot better than a wet marine climate. I would try to get a look at the cam and if at all possible. It probably wouldn't be doable, but if you could put a deposit on the aircraft and then get permission run it for 15-20 hours and check the oil filter for metal, that should tell you what you need to know.

Good luck.
 
Metal analysis of the filter seems like a pretty good check? I agree compressions tell you nothing. Can there be internal metal problems and they not show up in an oil change after flying a few hours?
 
An engine sitting idle for a long period can't be good, having it in a climate controlled environment will/would definitely reduce the possibility/severity of damage. I'd steer clear of one that wasn't in a climate controlled environment.
 
Not necessarily. An airplane flown in cold temps and then parked in a warm hangar is definitely a corrosion risk. More so than if the plane parked out in the cold. The perfect environment for an airplane engine at rest would be a very cold and dry place, and very cold takes care of the dry part. Corrosion increases with temperature. Factor that in.
 
bflynn said:
Metal analysis of the filter seems like a pretty good check? I agree compressions tell you nothing. Can there be internal metal problems and they not show up in an oil change after flying a few hours?
Click to expand...
The IA's I have dealt with have told me metal in the filter(or absence of) is a pretty solid indicator of cam corrosion. The problem is, you really need to analyze the filter after 15-20 hours of run time. If you check the filter on a pre-buy, you have to take the owner's word that they didn't just install a new clean filter....
 
My experience with cam corrosion wasn't accompanied by metal in the filter. Oil analysis would have noticed high iron but one oil analysis report isn't grounds to disassemble.
 
Stewartb said:
Not necessarily. An airplane flown in cold temps and then parked in a warm hangar is definitely a corrosion risk. More so than if the plane parked out in the cold. The perfect environment for an airplane engine at rest would be a very cold and dry place, and very cold takes care of the dry part. Corrosion increases with temperature. Factor that in.
Click to expand...
Is that how it normally works? Aircraft wait outside until engines cool before being brought inside, maybe in some cases.
Some here will understand the difference in why I wrote "climate controlled" and not just "heated".
 
Stewartb said:
My experience with cam corrosion wasn't accompanied by metal in the filter. Oil analysis would have noticed high iron but one oil analysis report isn't grounds to disassemble.
Click to expand...
So you are saying that you had significant cam corrosion, but you did not get any metal in your oil filter? In every case I've been around, making metal is the primary symptom.
 
edo2000 said:
So you are saying that you had significant cam corrosion, but you did not get any metal in your oil filter? In every case I've been around, making metal is the primary symptom.
Click to expand...

Yes, like the cam surface dissolved rather than flaked. And while the cam surface looked bad and had lots of pitting there was no spalling and the followers were okay.
 
There have been numerous threads on engine corrosion, and we've discussed the amount of atmospheric moisture that can possibly enter the case due to thermal expansion and contraction of the surrounding air. It's very small.

The chief culprit in engine corrosion is the water that is a byproduct of combustion. Aircraft engines are notoriously leaky things, with plenty of blowby past the rings, especially when the engine hasn't warmed up much. Air-cooled engines need those clearances to prevent seizure when someone closes the throttle in a fast glide and the cylinders contract around those hot pistons. Some of that blowby is water vapor, and it gets into the case and condenses there, mixing with the oil. In the presence of metals, which present an electrolytic reaction between the oil and water, acids form, and those acids eat the engine.

Ground-running the engine is very bad for it. If you start it, fly it. Fly it for some time to boil off the water that got in there while it was cold. The worst corrosion I have seen is in engines that were ground run "to circulate the oil and prevent corrosion." It doesn't work. Don't do it.
 
Forrest Gump voice on:

"Dan always had a way of 'splainin thangs to me so that they make sense."

Forrest Gump voice off
 
AlleyCat67 said:
Hi POA...

I'm looking at buying an AA5B (Tiger) that has sat essentially idle for several years. It was hangared in a dry climate (California), but there's certainly the potential for corrosion issues with the O-360. Part of me thinks I should just walk away. But... how effective would it be to have a cylinder pulled during pre-buy, and have the cam inspected for pitting? If that inspection turned out to be clean, would I have good reason to think that the engine would make TBO? Also, any ROM on the cost for that inspection during a pre-buy?

This is my first airplane purchase, and it's been pretty frustrating so far. It amazes me how many folks have let their planes sit around for months/years and then decide to sell. But I'm probably preaching to the choir on that...
Click to expand...
how long did it take.....before it ran outta gas? o_O
 
Dan Thomas said:
There have been numerous threads on engine corrosion, and we've discussed the amount of atmospheric moisture that can possibly enter the case due to thermal expansion and contraction of the surrounding air. It's very small.
Click to expand...
I believe the term "relative humidity" does apply, however small it may be.
 
Humidity inside an engine works like a greenhouse. In warm temps the air inside is muggy but there's no water showing. Cool off the outside temps and water runs off the ceiling and walls. Inside the engine the cam gets rained on. Water mixes with contaminates in used oil and makes acids. Acids eat metal. The perfect storage solution is to keep the engine filled with fresh oil and in a freezer. Hey, I just changed my oil and Alaska weather is below freezing right now. Perfect!

Hmm. Pull plugs and crank to get oil pressure? Interesting idea, but the manufacturers don't offer that advice in their storage instructions. Anti Rust oil with 7% Camguard is what I use for winter inactivity. That's more than most guys do.
 
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