Ask Paul: What are these aluminum specks?

Q: I lost the left mag on my O-540. When I took it apart, I found four aluminum specks in the top oil screen. I pulled the rear housing off and found the aluminum gear still in the engine. I sent it off for repairs to Tulsa, where they installed a new oil pump, shaft, gears and housing, as well as a new fuel pump and dry vaccum, and two rebuilt mags. I ran it for 1.5 hours, then pulled the screen and found a few specks again, but not as many as the first. Any ideas?

A: Let’s see if I’ve got this all figured out. You mentioned a left mag failure and that upon disassembly you found four aluminum specks in the pressure oil screen. This wouldn’t come as a surprise too me, but I’d also be curious to know what, if anything, you found in the oil suction screen in the oil sump.

When you talked about finding an aluminum gear still in the engine, I assume you are referring to the aluminum oil pump gear that has been the subject of several Lycoming service publications, including the most recent Lycoming Service Bulletin 524 plus Supplement Number 1 of SB524. This particular Service Bulletin supercedes several other Lycoming publications covering the same subject matter. The FAA also issued A.D. Note #96-09-10 and I assume the repair done in Tulsa brought the engine in compliance with the FAA A.D. Note and the other parts that were replaced allowed the engine to be returned to service.

The material you found in the pressure screen after 1.5 hours of operation may have been the result of the original failure. These specks may have been in the oil suction screen in the sump and overlooked during the cleaning and inspection following the failure. Depending on how much metal actually entered the engine during the initial failure and the total amount of disassembly and inspecting and cleaning that was accomplished, these recent specks may be nothing to be concerned about. Since you didn’t hint as to how much contamination may have gotten into the engine, it’s difficult to say whether this is some residual contamination as a result of inadequate cleaning or something else in the engine that is continuing to make metal.

I’d strongly recommend operating the engine to bring it up to normal operating temperature and then drain the oil through a paint strainer. I’d also flush and clean the oil pressure screen and its housing using an approved safety solvent and running all of it through a paint strainer. If there would still be an internal engine problem, I’d expect to see contamination in either paint strainer. Your findings here will dictate whether further investigation is required. Should you find little or no sign of contamination, then I’d continue operating the engine and repeat the same paint strainer routine during the next 25 hour oil change.

Just remember, cleaning and inspecting all screens and filters is required during each oil change. You would be shocked if you knew the number of engines that have never had the oil suction screen removed from the sump for cleaning and inspection since the engine originally left the Lycoming factory.


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


  1. Victor Nazarian says

    Hello there,
    I fly as air crew with the local Coast Guard Auxiliary (fixed wing, single & twin GA aircraft). Over the past 5 years I’ve actually gotten a significant amount of “stick” time when my pilots have been nice enough to let me sit in the right seat. In fact, because some of the pilots who’ve let me do a little flying are certified instructors I’m told that some of my time counts towards my certificate. I have my 3rd class med. / student pilot cert. and I’m thinking I’d like to get my private pilot certificate.
    OK, now the question. I’ve always had a fondness for Luscombe’s. My grandparents both worked at the N. J. factory (they’re in many of the promo photos) and my Grandfather did a significant amount of engineering design on the “type 50” and “type 65” before and during WWII. Should I learn to fly in a tail wheel airplane before a tricycle geared one or visa versa? I understand it’s actually harder in a tail dragger but that’s what my grandfather and great grandfather both learned in. One day I really want to own a Luscombe of my own, maybe with a nice STC’ed O-200 motor and a modern panel.

    Victor Nazarian

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