How long can a Lycoming (O-360) sit before it becomes a concern? I've been told most of my life that one of the worst things you can do to an aircraft engine is not run it. IIRC, you should get the oil hot enough (once a month?) to burn the accumulated moisture out of the engine. Is that correct?

I'm looking at several used aircraft and a surprising number of them have little to no use over the last year or two. When does this become a concern?

Thanks,
Lee

Dependent upon the conditions under which it’s been stored. Is it in the desert or a coastal town? Did they use preservation oil and desiccant plugs when sitting for a while? The typical problem area is the valve train on these engines. Even if it does have some corrosion starting on the cam or lifters, it will usually take a while to manifest (50-100 hours). Only sure way is to pull a cylinder, though most owners aren’t going to let that happen during a prebuy as it can induce issues of its own.

After several recent pre buys on airplanes that are sitting it seems as if you park it and don’t touch or more the prop they are more likely to be in good shape. But it’s mostly a crapshoot. Pull a cylinder and look at the cam


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My understanding that you cant easily see all the cam and associated valve train by pulling a cylinder.

Oil change interval is a big consideration, not just tach hours but calendar time too. Lycoming states every 4 months or specified tach time, whichever comes first.

Airplane should be flown more than once a month, weekly is best. When flown it should be flown long enough to burn any moisture out of the engine. Getting the oil temp up is important. Quick hops or 30 minute flights can be more detrimental than not flying at all since all they do is generate moisture inside the engine but don’t allow the moisture to be burned off. Periodic ground run ups are the worst thing you could do contrary to what some think.

If airplane sits and has been properly “pickled” with storage oil and is in a favorable climate or heated hangar then there is less likelihood of rust.

Again, oil changes at the correct intervals are key.

Lycoming has good info on this subject.

Kurt

One in Georgia, Alabama, and Texas. All of them stored in hangars and nothing special was done when "stored". They have sat anywhere from 6 to 20 months, Their consistent story goes, "life got in the way of flying and before I knew it, the non-flying days turned into weeks that became months."

I understand that there are too many variables for a Deal / No Deal answer, but is there a "rule of thumb" when the engine must be inspected after sitting for extended periods of time?

Thanks,
Lee

Lee, I don’t know of any “rule of thumb” on the subject. It’s pretty much a gut feel, “do you feel lucky” kind of thing. Like I said earlier, don’t just look at how long its been sitting but the oil change intervals and how long ago was overhaul and how many hours flown divided by calendar time.

I was helping a buddy look for an airplane a month ago, we came across a lot of airplanes that had low time but a lot of sitting and some had yearly oil changes instead of every 4 months which Lycoming calls for, yikes! I got a worst case scenario quote of an overhaul from Penn-Yann, new cam, cylinders, mags and so on, very complete overhaul. Price was $24,900 so use that as a measuring stick if worst case scenario pops up. Keep in mind, if this were to happen, you would be in the hole but you would have some added value in a fresh overhaul from a reputable shop. Lots to consider.

Kurt

The age old Continental/Lycoming sitting debate. Lycoming does have a cam that sits free of the oil bath and is only coated when the engine runs. The Continental engines design, the cam is lower and has the benefit of being in the oil. Now that being said, one would think that the cam pitting would not happen to Continentals. Well not true. My bud just had his $20K cam lifters & cylinders bill on a 1,000 hr factory Reman Continental. He flies twice a month at a minimum and lives in Phoenix.

So, if you have a Lycoming, there where a few things you should do. Lycoming used to make an additive you put in your oil which had the aromatic effect to keep you cam coated all the time. This additive is in Aeroshell 100W Plus now. I use it and use a general preservative when I ship aircraft across the sea. They do work. Conditions and care will tell you if you will have problems. Sometimes you just get bad metal used in the manufacturing and you will get the $20K bill, regardless of manufacturer.

If you get desiccator plugs, unless they are in sealed bags, you need to re-activate the silica gel. Put the beads (just the beads, empty out the plug) in an oven for 2 hours at 180°-250°. This drives out the moisture in them and makes them thirsty again.

Borescope is easy, non invasive and at least you get a look at cylinder walls and valves.

It really is a crap shoot, and a pretty expensive one at that. When I bought my airplane, the engine (O-360) had about 930 hours on it, but in the last few years, the airplane had flown less than 10 hours between annuals. It was always hangared, in the Tulsa, OK, area, so a pretty dry climate. From all I could tell, I should have had another 1000 hours of relatively trouble free use.

Well, 15 hours from the time I left Tulsa, the engine threw a rod through the top of the case, and I landed in a field. A couple months later and $23,000, I had a "new" hand-built engine that now has about 960 hours on it, and except for some cylinder work on one of the cylinders a couple of years ago, has been pretty reliable. But why did that happen? The engine builder surmised that a bearing had spun, cutting off the oil supply, and that was probably caused by relatively little use between annuals.

Does that mean that every engine subjected to minimal use will crap out early? Not necessarily. My first airplane was a 1970 Skylane, which my pards and I bought in 1975 with all of 300 hours on it--all put on during the first two years, and the airplane then sat without being run at all for the next 3 years. That's a 1600 hour TBO engine (O-470). At about 1200 hours, i.e., 900 hours after we bought it, the cylinders needed to be topped. That was a mistake, because only about 150 hours later, we had to overhaul it completely. We would have saved some money if we'd just overhauled it at 1200 hours instead of waiting another year. So that engine probably suffered some from disuse, not nearly as bad as my Lycoming, but we still had 900 pretty trouble-free hours from it.

I have heard of others who bought barn-finds that hadn't been flown in 15-20 years, and all they had to do was change the oil and install a new battery, to begin what turned out to be several years of totally trouble-free operation.

So you never can tell for certain. And frankly, even an engine that has been run and frequently flown isn't guaranteed to keep running reliably. Stuff happens.

Cary

I am far from an expert on aero engines but have been around neglected motors my whole life. I'm cheap.

It is really a luck thing, you can't say whether a neglected motor will go to TBO or not. I think even with the most stringent examination you still can't tell for sure.

So you should price that risk into any transaction on a motor that has sat, or had little run time. If in doubt, or if the seller won't price the risk in, walk away.

That said we all get emotional about a purchase and may decide to roll the dice. Just be aware that that is exactly what you are doing.

I recently completed a pre-buy on a C180 in which the seller agreed to our removing the rockers, pushrods, pushrod tubes and lifters. Got to see the lifters, all cam lobes and, with a borescope much of the crank and lower engine components. Only took a few hours, was reasonably non-invasive and informative. Reassembled with new pushrod tube seals.

Thanks for the advice. I'll look for my lucky dice and walk into the purchase with eyes open

-Lee

Someone here wisely said that they prefer the engine be runout on aircraft they buy so they can just factor an overhaul into the cost. It's a good approach if you can get the seller to acknowledge the value reduction for engine.

Zzz wrote:Someone here wisely said that they prefer the engine be runout on aircraft they buy so they can just factor an overhaul into the cost. It's a good approach if you can get the seller to acknowledge the value reduction for engine.

That was me. Ensures that both you as the buyer and they as the seller have the same understanding of the engine condition. But when the engine is advertised as 500SMOH and you discover the overhaul was 30+ years ago, they seem to think it is a low time engine and you are buying a serious unknown.