Question About Engine Corrosion and Spalling

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OntheNumbers
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Question About Engine Corrosion and Spalling

Post by OntheNumbers »

My engine is in for overhaul and an initial report indicates there was some spalling and corrosion internally - no futher details than that at the moment. The engine is a Lycoming O-360.

Over the 7 years I've owned the plane, I've changed the oil every 4 months, opened the oil filter and searched for metallic bits and sent the oil for analysis (I've got a good collection of reports now!). None of those tests have revealed any significant chunks of metal or quantities of trace metals in the oil that would suggest spalling. My understanding of the mechanisms related to spalling is that once the outer coating of hardened metal is eaten-into, the underlying softer metal is a sitting duck for continued spalling.

My question is, how could any spalling have snuck through over the past 7 years without me finding anything in the oil or the oil filters that would substantiate that claim? And, if the spalling is older than 7 years, then it should have continued during my ownership due to that sitting duck issue I mentioned above - it doesn't seem like it would just suddenly stop once it started.

Any wisdom on this topic would be appreciated,

Thanks for reading.
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ahramin
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Re: Question About Engine Corrosion and Spalling

Post by ahramin »

Sounds like a good question for the Savvy team but if the spalling started before your oil monitoring then you wouldn't see a spike in the oil monitoring, just steady wear.

On my last overhaul one cam lobe was almost completely gone. Nothing in the filter.
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corethatthermal
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Re: Question About Engine Corrosion and Spalling

Post by corethatthermal »

The oil analysis takes the mid flow oil when draining NOT a sample from the oil filter element. Oil filters collect metal. Sumps collect metal ( at the bottom, depending on the oil type as well ) Generally, heavy metal is not suspended in the oil . I don't consider SOAP a perfect tool for determining what all is going on in the innerds. Also, not all engines are built the same some cams are not deeply hardened either.( Especially overhauled ones) Poor manufacturing and the operating conditions and pilot abuse is also a big factor. EVEN the choice of oil can be the difference between an engine bottom end that goes to O/H.
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OntheNumbers
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Re: Question About Engine Corrosion and Spalling

Post by OntheNumbers »

OK, thanks for the insights. Sounds like it's possible to have spalling without seeing much evidence of it in the oil or the filter - to me that says the particles of metal coming off the cams must be very small to go unnoticed and the process must have taken a long time - which I suppose is possible in this case, my engine's had a run of ~35 years since the last overhaul with just over 1300 hours on it.

Cheers
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ahramin
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Re: Question About Engine Corrosion and Spalling

Post by ahramin »

35 years? I'd say that engine doesn't owe anyone anything. I'm starting from a fresh overhaul, flying every two weeks, changing oil every 4 months, oil filter inspections, boroscope, SOAP. I'm hoping to get 20 years.
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OntheNumbers
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Re: Question About Engine Corrosion and Spalling

Post by OntheNumbers »

Yeah, I've owned it for 7 and it's not shown any signs of needing attention yet, based on the same MO that you follow, at least since I've owned it. It's a prop strike that has influenced the decision to get the overhaul done (not me flying at the time) - and a stupid one, taking out a taxiway light.
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ahramin
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Re: Question About Engine Corrosion and Spalling

Post by ahramin »

YPW?
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Choppermech1986
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Re: Question About Engine Corrosion and Spalling

Post by Choppermech1986 »

It would really help to see photos. If your engine shop can't send you a photo (next to a recent newspaper ideally) of the damage, I'd be hesitant to agree to too much.

The guys above have covered most of it.
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