What should I do about rust in the barrels of cylinders?

Q: I read some of the material you have posted and was very impressed. I have a question about finding rust in the barrels of the cylinders.

Here is the situation: A customer is looking to buy a Piper Lance II. It was asked that we do an annual instead of a pre-buy inspection. The engine is a reman from Lycoming with 224.1 hours since November 2012.

There are a few squawks. One of them was finding rust in the barrels and they were all wet.

I have a better borescope on the way from another customer.

I have heard from a couple other pilots who stated that something like that happened to them. Their scenario was they had an oil sample done and the A&P advised them to fly it for 50 hours and let’s check it again. They say it cleared up. Keep in mind these guys flew often.

Have you every heard of this? The customer who is planning on buying the Lance plans to put 100 to 200 hours a year on it.

My first thought when I saw the rust was honing the barrels in accordance with Lycoming Service Instruction 1014M. That is the only way I know to take care of the problem.

Steven Bible, Precision Aviation Services

A: Steven, this subject should be of interest to many, especially those who are in a similar situation as you where a customer is considering buying a used aircraft. I commend your customer for requesting you do an annual inspection versus a pre-buy inspection because it provides a much better overall picture of the aircraft. With the cost of aircraft today, it’s a good investment.

With regard to the observed rust in the cylinders, this is, as you know, not a good thing. While there are varying degrees of corrosion in cylinders, most of it begins from extended periods of inactivity. When you couple this with infrequent oil and filter changes, it just seems to add insult to injury.

Of course we must not overlook the location where the aircraft is based as a contributing factor. As an example, if the aircraft is based in a hot, humid air environment and is not operated frequently, the likely possibility of internal corrosion increases versus an aircraft that is based in a high desert, dry climate environment.

So, let’s think about what you should do in your particular situation. First, I would review the engine logbook, checking for frequency of operation and of oil and filter changes.

If this engine has been using oil analysis, this could provide some good information regarding the contaminates found in the oil. It’s very important to know that oil analysis is only a good tool if it’s done on a regular basis so that the results of each analysis can be viewed as a trend analysis.

NOTE: Taking one oil sample and trying to determine the health of an engine is absolutely a waste of your time and money simply because you have no previous data to compare it with.

I’d also recommend you remove and cut the oil filter open and closely inspect the filter for any sign of metal contamination. Doing this may preclude any further inspection depending on the amount of contaminates observed and possibly make a decision for you.

My suggestion for you would be during your inspection with the “better scope,” pick the worst looking cylinder, and if you are experienced with using a good scope, try to determine if the corrosion is just surface rust or can deep pitting be observed?

From my experience, if the corrosion is just surface rust, then it is likely that continuing operation of the engine may heal the cylinders. Should this be the case in your situation, I’d suggest you change the oil and oil filter and fly the aircraft for 10 hours and inspect the filter again.

However, if pitting is observed, then I’d recommend removing the cylinder showing the worst corrosion for further inspection. If the pitting is severe, I’d say there may be a possibility of still saving the cylinders by having them honed by a reputable cylinder repair shop that uses a large vertical hone machine or something equivalent.

My past experience where heavy corrosion was evident has shown that honing the cylinders on a big vertical hone removed the corrosion by removing no more than .003″ while still keeping the cylinders within tolerance and allowing the cylinders to continue in service to TBO.

Keep in mind that every circumstance will be different. The typical honing tools used with a drill motor will not be sufficient to remove the type of corrosion I expect you may dealing with.

Please keep in mind that once the cylinders are honed, you must install new piston rings and break in the cylinders using a mineral base oil in accordance with Lycoming Service Instruction 1014M.

I’ll leave the ball in your court now, but hopefully what I’ve mentioned will give you something to consider. It certainly isn’t the end of the world, but if contamination is observed in the oil filter, then I become concerned about possible contamination of crankshaft, connecting rod and camshaft bearing surfaces. Any possible contamination of these areas could possibly lead to nasty things happening, and all would carry a very high price tag to repair or replace.

Once you get beyond this temporary inconvenience and the aircraft is purchased and your customer begins to fly as frequently as you mentioned, all will be well once again.