Ask Paul: Use it or lose it

Q: I am considering buying a plane with a Lycoming 540 factory rebuilt engine. TSOH is 50 hours. The problem is the engine was installed five years ago with a new turbo and the owner has not flown it much since, although it has flown a few hours recently.

There is a lot of chatter about unflown engines rusting inside and not making it to TBO. I don’t need to make it to TBO, but I don’t want it to go south within the first year or two after purchase. How much of this chatter is exaggerated? Is an engine that sat like that such a huge problem that it should be avoided? Is is possible that a low-time factory rebuilt can be rendered useless that easily?

R. GASTON, via email

A: Here we go with one of those deals that look good up front, but may not turn out so good in the end. I admire you for being sharp enough to ask questions before taking the leap, but just in case you already put your money on the table, let’s look at a few things that may help save the bacon.

The “chatter” you hear regarding engines rusting inside and not reaching TBO is closer to fact than fiction. While it certainly doesn’t mean this engine should be avoided, there are certain things that should be done prior to any final decision. Yes, it is possible that a factory rebuilt engine, or any engine as far as that goes, could be rendered unairworthy from improper storage or lack of use. Inactivity in anything, including our own bodies, works against us. As the old saying goes: “Use it or lose it.”

When an engine has been exposed to long periods of inactivity, whether it be installed on an aircraft or stored on a hangar floor, we need to take a close look at it before putting it back into service. This particular case, where the engine had been overhauled and flown for a few hours, then sat idle for some period, then flown again recently, makes me nervous because we don’t know what, if anything, was done to try to preserve the engine prior to its extended period of inactivity.

Let’s assume nothing was done and then, after some period of time, the engine was flown for a few hours. The first thing I’d do is remove the oil filter, cut it and inspect it for any debris that may indicate internal corrosion. If you aren’t familiar with the proper way to do this, I’d suggest you refer to a copy of the Champion Aviation Service Manual AV6-R. You can check out this procedure by going to the Champion website and click on Products, then Oil Filters, then AV6-R, page 25.

Regardless of your findings, I’d go a farther to satisfy myself that we didn’t have an internal corrosion issue. A good borescope inspection would tell us quickly if there was any corrosion in the cylinders. If corrosion is observed in any or all cylinders, that will tell us what our next step will be. Let’s say we only notice a slight discoloration on a couple of the cylinders. It’s this type of situation that requires someone with experience using the borescope because, if there is only slight discoloration, you may be able to continue the engine in service with no further concern after changing the oil and installing a new oil filter. However, if there is a possibility the corrosion has caused pitting on the cylinder wall, then the decision has been made for you. The cylinder must be removed and honed to remove the pitting.

If there is any doubt about the internal condition of the cylinder or cylinders, then removal should take place. Even though this may seem inconvenient, it affords the opportunity of taking a close look at the internal engine parts. Using a flashlight and a good inspection mirror, you can closely inspect the condition of the cam lobes and corresponding tappet bodies for indications of corrosion. Any corrosion in these areas will determine whether the engine must be taken out of service for major repair.

Let’s assume there is no problem in this area and we can get back to our corrective action on the cylinders. Cylinders may be sent to a good overhaul shop for proper honing. Typically, cylinders that have corrosion can be cleaned up by honing no more than .001 to .003 from the cylinder bore. If they were new factory cylinders, this amount being removed would still keep them in new cylinder dimensional tolerance. Once the cylinders are honed, new piston rings should be installed and the normal engine break-in procedure followed. You mentioned that a new turbo had been installed, so please keep in mind that all turbocharged Lycoming engines must be broken-in on ashless dispersant oil only.

I wish there were a more basic or simple answer regarding an engine of this type, but there are just too many circumstances surrounding engines that end up in a condition like this. An engine could be in a hot humid climate, which makes matters worse when compared to an engine in a cold, dry climate, so you can understand why each engine has to be taken on a case-by-case basis.

Good luck and remember, regardless of what you decide, whenever you finally get something flying, be sure to fly it frequently. After all, isn’t that why we buy an aircraft in the first place?

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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