"Inspected oil filter, found no metal" - myth or reality?

[AV8R_87]

I've seen logbook entries and people posting on forums (this included) with the claim that their engine doesn't make any metal.
I'm having trouble believing that is 100% accurate. Is it just a case of people looking at the filter, seeing a few specs and dismissing that as normal wear and tear vs an engine that's tearing itself apart?

Just looking at the cylinder wear limits for an O-320, quick back of the envelope math would indicate that over a 2000 hour life, a set of cylinders wearing down to minimum would generate about 3.5 ounces of metal.
That's close to a tenth of an ounce per oil change, assuming even wear over 40 oil changes.

Spreading those steel filings on a layer 0.02" thick would give you a 1.5"x1.5" square. Yes, cylinders probably wear less than that, but even at an eighth of that wear you'd still get a patch of filings that's a 0.5" square. And then there's other things wearing inside the engine (rings, gears, bearings, cams and lifters).

There is wear inside those engines, otherwise we'd never need to overhaul them. Flight school planes usually don't sit enough for cam corrosion to be a factor, yet they still need overhauling. There has to be some amount of metal being generated all the time. Why do we have all those people that say "my engine doesn't make any metal"?

What am I missing?

 

[Silvaire]

Without analyzing your math I think maybe you are mentally time compressing the wear and assuming it comes through as "steel filings" rather than microscopic particles that remain suspended in the oil and are not entrapped by the filter.

 

[ateamer]

It’s more of a synonym for “inspected filter element - particles found within limits of Lycoming SB 480F for continued operation without corrective action needed.”

 

[Daleandee]

Unless the metal found in the filter has a readable part number it don't really count ...

 

[MRC01]

It’s more of a synonym for “inspected filter element - particles found within limits of Lycoming SB 480F for continued operation without corrective action needed.”

Indeed. Which says, in part (though there is a lot more):
If more than five small particulates are on almost every panel in the oil filter element or if there
is a 1/4 teaspoon full of metallic particles from an oil pressure screen or oil suction screen, these metallic
particles require immediate analysis because they can be an indication of an engine component being worn
or damaged.

 

[Checkout_my_Six]

my engine isn't making any "visible" metal.....at +1,300 hrs TSMOH.

 

[Bell206]

What am I missing?

A lot of the normal wear metal particles are so small they do not get caught in the filter and are disposed at every oil change. However, those metals are seen in oil analysis reports.

 

[AV8R_87]

Without analyzing your math I think maybe you are mentally time compressing the wear and assuming it comes through as "steel filings" rather than microscopic particles that remain suspended in the oil and are not entrapped by the filter.

I'm not thinking steel shavings, but fine steel dust that would be retained by the filter or the magnet that used to be in the filter.

It’s more of a synonym for “inspected filter element - particles found within limits of Lycoming SB 480F for continued operation without corrective action needed.”

So like the FDA labeling guidelines on trans fats? If it's less than one gram per serving you can claim zero trans fats?

Thanks for the SB, nice to know about it. I wonder why it isn't referenced in the logbook entries.

 

[OneCharlieTango]

A lot of the normal wear metal particles are so small they do not get caught in the filter and are disposed at every oil change. However, those metals are seen in oil analysis reports.

Where they cause worry but indicate nothing.

 

[mondtster]

If you wash the oil filter element out in solvent you will oftentimes find metal in it. A lot of people just spread the pleats in the filter and look for big pieces, which won’t reveal as much, or what is found is so minor that the “no metal found” report is used. There are also places within the engine that can trap contaminates and it will reside there until the engine is disassembled for repair/overhaul, so not all the metal will even make it to the oil filter or be purged with the oil at an oil change.

 

[Bell206]

Where they cause worry but indicate nothing.

Only if you do not understand how to read the oil reports or do not understand the purpose of the analysis.

 

[Silvaire]

I'm not thinking steel shavings, but fine steel dust that would be retained by the filter or the magnet that used to be in the filter.

Same concept in that your "fine steel dust" are giant boulders in comparison to the microscopic particles that the normal wear process creates.

I'd add that the majority of wear is at start-up. A correctly functioning engine at operating temperature and oil pressure isn't going to have any metal to metal contact, there will be a 1 to 20 micron film of oil on all of the bearing surfaces.

 

[AV8R_87]

Pulled a couple oil analysis reports from Blackstone. They claim the average iron content (for an O-320) is 35 parts per million. Assuming you're draining 7 quarts out of the engine (unlikely, that number is probably closer to 5, but I'm being generous) that amounts to 0.21 grams, or less than 1/100 of an ounce of iron in your drained oil. That's less than 8% of the theoretical amount of steel that would be shed by the cylinders, assuming even wear to max allowable limits by the time that engine hits TBO.

Even if we assume cylinders could last 4000 hours before they wear down to minimum, so they only shed half the metal per oil change, it still doesn't add up.

 

[geezer]

Nit pickers stay away from my "facts" they are very loosely assembled.

AV8R_87 is making some radically wrong assumptions.

First, the engine is rebuilt when the cylinders have a lot of potential life in them.
When the rings are worn enough to cause low compression, the cylinders can be removed, cleaned up and honed, and returned to service with new rings on the pistons.

When these rings are worn enough that there is poor compression, the cylinders may be removed, cleaned up, honed if needed, and fitted with oversize pistons and rings, and again returned to service.

Cleaning up and honing potentially removes as much metal from the cylinders as the ring wear.

At an average of 1800 hours per set of rings, this is a 5400 hours of service on the cylinders, to use for your calculation of how many ounces of steel should be in a filter at oil change time.

We did about that on our C 200 powered C 150, the original new cylinders lasted more than 2000 hours, the last "top overhaul" lasted about 1600 hours. Putting those cylinders on the lath to true them to cylindrical put a lot of ounces of steel on the shop floor.

Second, the engine "used" quarts of oil between changes, the metal carried in that oil went out the exhaust or through the crankcase vent. All that lost oil has to be accounted for as a destination of lost metal.

Third, when you pull the crankcase off for an overhaul, you will find the large pieces of metal resident there, not picked up by the oil pump. That is why a good mechanic will do a thorough crankcase flush with his "top overhaul", which helps assure nothing bad happens to the pump.

We had a skilled mechanic, with a well equipped shop, and we enjoyed long periods between actual full overhauls. Unfortunately, he was not at our airport, so we had to be sure that we did the top overhauls while the engine was still healthy, and if a weak cylinder was found when propping during preflight, we flew over to his shop to check what was needed.

All this ignores such things a valves, which some times cause problems prematurely.

Our plane flew frequently, had regular oil changes, and virtually never had a ground run without flying. We flew a minimum of a quarter hour before doing our oil changes to get a maximum of the particles suspended in the hot oil during the drain out. 10 shared owners, 6 active students.

For the real mechanics here, remember, this is very simplified for the OP. The plane had a set of brand new cylinders and complete overhaul when we bought it, and I do not think we ever put a new cylinder on it while we owned it. 1970's and '80's period in history.

 

[AV8R_87]

AV8R_87 is making some radically wrong assumptions.

That's a bit over the top. I'd agree with you if I was off by a couple orders of magnitude.
I mentioned that I'm not even trying to add up any wear metal from rings, cams, lifters and gears. That amounts to some value that is definitely not zero.

How much oil do you add between changes? Three quarts? Let's make it four, to be generous. Now your used oil (including burnt/blowby) holds a total of 0.33 grams of iron.

Let's also go with your 5400 hours total life, although if you posted that on Wikipedia you'd get a "Citation Needed".
I'd like to hear from people who measured cylinder bore diameters at overhauls to see what the actual numbees are.

That puts you at about 1 gram of iron wearing out of the cylinders per oil change. We've generously accounted for one third of that in the oil.
The other 0.66 grams, spread out in a layer 0.02" thick, would give you a square a bit over 3/4" on each side.

Spreading those steel filings on a layer 0.02" thick would give you a 1.5"x1.5" square. Yes, cylinders probably wear less than that, but even at an eighth of that wear you'd still get a patch of filings that's a 0.5" square.

I tried erring a lot on the side of caution even in my opening post, allowing for an error in my assumption that amounted to almost an order of magnitude. Yes, I neglected to consider the iron that stays in the oil (thank you all who pointed that out) which ends up accounting for 25-33% of the total, assuming your conservative wear figures.

Yet even this way, it still feels like people should be observing more metal in their oil filters than we hear about. It still doesn't fully add up.

 

[Silvaire]

...it still doesn't add up.

Well, what you are saying is that reality doesn't add up with your "back of the envelope math" so where would you suspect the error lies?

 

[AV8R_87]

Prove me wrong with actual facts, then. Cylinder measurements at overhaul. Wash your filter paper in a solvent and separate all trapped metal. Weigh it and report back.

 

[geezer]

One of the big things here is the clearly visible bits of metal that do not get sucked up by the oil pump, and just lie on the bottom of the crank case. Some of that flushes out with the oil change, and for a while we had a magnet in the bottom of our plastic oil change bucket, but it got lost. We were surprised that the magnet had much more recoverable metal from the bucket than the filter. The metal from the bucket was much larger (still very small) than the metal pulled from the filter paper, and had a gritty feel. Filter paper bits on the magnet were more of a paste consistency, rather than "bits".

Cleaning the magnet between uses is a pain, nobody liked to use it.

Later, someone found an automotive drainplug with an integral magnet, and it might have been mistakenly installed in the plane, and it may have acquired more fuzz than the drain bucket magnet, and presumably prevented a lot of metal reaching the oil pump.

 

[TCABM]

That's a bit over the top. … It still doesn't fully add up.

How many filters have you cut?

 

[Mxfarm]

I've never cut a filter, but do oil analysis on every oil change. Trends there are what is important. If I were to cut a filter and be able find metal, I'd stop flying that engine immediately.

 

[AV8R_87]

How many filters have you cut?

Not that many - hence why I'd like to hear from people that have opened up a bunch of them and have done more than just glance at the filter paper. Run a magnet through all the pleats, rinse the filter, stuff like that.

 

[MRC01]

I've never cut a filter, but do oil analysis on every oil change. Trends there are what is important. If I were to cut a filter and be able find metal, I'd stop flying that engine immediately.

Cutting open the oil filter and inspecting the media is part of "acceptable methods, techniques and practices". If you aren't doing it, then you are not doing the oil change properly according to the FAA. So you should! UOA augments but cannot replace doing this because each detects different kinds of material. You will always find at least some metal in the filter, even with a healthy engine. The question is what kind of metal, size and quantity of particles, etc. The Lycoming doc referenced above is an excellent guide. They wrote it for a reason - not only so people know when the engine needs attention, but also so people don't unnecessarily ground perfectly healthy and airworthy engines.

 

[Dan Thomas]

Putting those cylinders on the lath to true them to cylindrical put a lot of ounces of steel on the shop floor

I over 50 years of aviation I have never heard of that. I'd like to see a picture.

I operated cylinder resizing equipment for thousands of hours. I have "cleaned up" aircraft cylinders in a rigid honing machine like the Sunnen CK-10 orCV-616, the industry standard. Chucking an aircraft cylinder in a lathe would be extremely difficult and counterproductive, especially once you know that the largest oversize is only .010". And yes, I have thousands of hours of lathe experience. And crankshaft grinding experience.

First, the engine is rebuilt when the cylinders have a lot of potential life in them.

The OP is making the assumption that the cylinders are worn to limits at TBO. That's a very rare case, and lots of metal would be noted for a long time. Corrosion is the usual culprit there.

The majority of the usual stuff will be at the molecular level. Tiny stuff that stays suspended for a long time, and goes out at oil drain time. Some of it settles as sludge in the sump, and that's why we take oil samples midway through the drain, to catch a minimum of that.

Our flight school Lycomings went to TBO with almost no metal found in the filters, and compressions were still in the high 70s. Nothing in those engines was worn to anywhere near service limits. They would fly a homebuilt for another 2000 hours.

 

[geezer]

Dan is completely right here.

My term of putting the cylinder on a lathe is wrong, it is a honing machine.

As he says, the wear particles are normally in the molecular size, and on the magnet, a fine paste.

Thank you for weighing in with the usual detailed facts from a career of maintaining engines. As noted at the beginning of my first post, I was using LOOSLEY accurate information, which is what I have. The big point is that most of the wear metal is not going to be found in the filter. The OP seemed to think it should.

 

[Dan Thomas]

The big point is that most of the wear metal is not going to be found in the filter. The OP seemed to think it should.

Some will even get blown out of the exhaust. Flame tends to ablate (erode) surfaces. Particles left behind on the piston downstroke might be more likely to get exhausted.

If the filter got it all, it would then get all the carbon, too, and the oil would only be somewhat darkened by the heat, still mostly transparent, not so opaque and black.

 

[AV8R_87]

The OP is making the assumption that the cylinders are worn to limits at TBO. That's a very rare case, and lots of metal would be noted for a long time. Corrosion is the usual culprit there.

This is educational.
Would you happen to have actual bore wear numbers for a 2000hr cylinder? I used the 5.1305" max allowable wear, starting with a new cylinder at 5.1245".

Our flight school Lycomings went to TBO with almost no metal found in the filters, and compressions were still in the high 70s.

What would be your definition of "almost no metal" (serious question)?

 

[Bell206]

Yet even this way, it still feels like people should be observing more metal in their oil filters than we hear about. It still doesn't fully add up.

The main reason is your basis for metal amounts are assumptions and guesses to include Blackstone’s numbers. Plus each engine and especially recip engines are unique to themselves in how they wear, turn oil black, etc. So there is no real benchmark to compare to.

While I don’t follow the point of your quest, I can tell you from my experience that those numbers will never add up. For example, I’ve seen engines that make 3x more metal than an engine of the exact same model number but burn less oil than the latter engine that makes less metal… yet both engines make it past OH with no operational issues.

Perhaps a new hobby counting stars or something you can actually see and quantify?

I've never cut a filter, but do oil analysis on every oil change. Trends there are what is important. If I were to cut a filter and be able find metal, I'd stop flying that engine immediately.

FYI: using oil analysis does not null and void following other recommendations like checking filter elements. Not all failure modes will trend in an oil analysis. Full stop. Oil analysis is merely one tool in monitoring your engine health which includes filter checks, compression checks, and so on. Unfortunately you may be setting yourself up to fail more than you think.

 

[Kesk]

You will know when it's bad with zero doubt in your mind.

One time I drained oil and it was the blackest oil I'd ever seen. Cut open the filter and it was full of chrome. Someone very high up broke a piston ring (forget which one) when installing a new cylinder and ordered replacements. The replacement was not the right ring.

 

[AV8R_87]

Perhaps a new hobby counting stars or something you can actually see and quantify?

Good thing you weren't around when the Wrights were trying to figure out why their gliders weren't flying as well as the (incorrect) lift equation was predicting they should.

Blackstone's fleet average number is better than anything that has been posted in thread so far (zilch). It is a good starting point.

I’ve seen engines that make 3x more metal than an engine of the exact same model

Here's an improvement. We went from the "no metal found" to "metal" and "3x more metal". That's exactly the point. A lot of logbook entries claim they found none. Never. In the whole lifetime of that engine. Misleading at best.

And that's what I'm trying to understand. What to realistically expect out of an oil filter. It seems (based on comments so far) that not a lot of people use a magnet (or solvent) when inspecting a filter.

 

[Silvaire]

Prove me wrong with actual facts, then. Cylinder measurements at overhaul. Wash your filter paper in a solvent and separate all trapped metal. Weigh it and report back.

Okay, as a retired A&P who has cut open and washed a bunch of filters over the past 45 years here's my report:

your math doesn't add up.

 

[Checkout_my_Six]

Her ya go…..

Engines make "THREE" different size metal particles....

Large - failure modes that produce "chunks" will not find their way into the filter or metal analysis....but remain in the bottom of the oil pan and can be discovered by inspecting the oil screen.
Medium - failure modes producing granular, visible flakes, will get collected in the oil filter and can be inspected by cutting the filter.
Small - microscopic or metal not visible to the eye and measurable in parts per million....will not be seen in the filter or screen....and failure modes producing fine metal....from wear....can be detected using oil analysis.

So....one size oil indication does not fit all....as those who think oil analysis is the magic indicator.....it is but one in the RCM tool box. (RCM -Reliability Centered Maintenance)

And....the physics of failure will determine which indicator works best.

Oil analysis is a kin to a kind of blood test.....it only shows fine, small, metals in the oil measured in parts per million. If the failure mode didn't create fine metal....the oil analysis will "not" indicate. What if the doc orders the wrong test?.....Can the doc still diagnose?

However, if the failure modes did make metal, just not "fine" metal. And, if the oil filter were cut and analyzed....along with checking the sump screen for larger sizes.....the combination of the three methods provide a clear indication of an impending problem.

On-condition maintenance requires "indicators", as a precursor, to predict an impending failure mode.....Oil analysis, again, is not a one stop shopping indicator......it is but one tool in the tool box.

Again....the physics of failure determine which type of indicators work best.

The key in any successful health monitoring system is to first identify the physics of failure and then determine "indicators" that identify the impending failure prior to catastrophic failure. In this case there are multiple failure modes producing various debris particulate sizes.....and several indicators are needed (oil analysis, filter media inspection, oil sump screen inspection), one for each failure mode type. Each of the different indicators alert a different impending catastrophic engine failure mode.

In addition to monitoring debris in the oil....one could of also monitor vibration at key locations on the engine. That worn gear would have likely generated a different "noise" signature as it developed excessive misalignment (a very common technique in other applications). Alerting on an out of bounds or range condition, just like we do with an engine monitor, would also been very effective catching this impending catastrophic gear failure.

 

[Dan Thomas]

This is educational.
Would you happen to have actual bore wear numbers for a 2000hr cylinder? I used the 5.1305" max allowable wear, starting with a new cylinder at 5.1245".

What would be your definition of "almost no metal" (serious question)?

A 2000 hour cylinder could be all over the place, wear-wise. I would bet that our 2000-hour flight school Lycs would have much, much less than the .006" of wear between your dimensions. Like I keep saying, an engine run on the ground "just to circulate the oil" will result in moisture in the crankcase, moisture that normally evaporates and leaves via the breather once the engine is flying and hot. Moisture in the crankcase mixes with the oil and forms, due to the presence of catalyzing metals, nitric, sulfuric and hydrochloric acids. Those acids eat the engine. That's where cam and lifter corrosion comes from, mostly, and I've seen too many pitted cylinders from it as well. Pitted cylinders eat the rings, and the rings eat the cylinders. Pitted valve stems can result in valve breakage and catastrophic engine damage.

Operating in dusty conditions with the typically worn-out, leaky airbox/carb heat flapper valve and/or induction bellows, is another good way to trash an engine. Many years ago an engineer from the Ramsey Piston Ring Company (I think they've been absorbed into some other outfit now) told me that their dyno tests found that one teaspoonful of silica dust (most common) fed slowly into the intake of an engine making power, would result in that engine being instantly worn out. When I was rebuilding thousands of compressors, poor maintenance of trucks or earthmoving equipment would trash that compressor in a few hours. Loose or leaking filtration.

"Almost no metal" means rinsing out the filter media in clean solvent, draining off most of the solvent, and examining what remains in that nice clean pail. One might find a very few tiny shiny flakes, and maybe a tiny bit of fuzz on a clean magnet.

 

[Bell206]

Blackstone's fleet average number is better than anything that has been posted in thread so far (zilch). It is a good starting point.

Not really. Blackstone’s or any oil sample company’s numbers only represent a limited percentage of all the metal in the oil. For example, normal procedure is to take the oil sample during the middle of the draining process. So if 50%+ of your metal wear particles drain out before you even take the sample, how do you quantify that loss in your results?

Actually, the optimum method to obtain oil samples is to draw it off the top as this provides a better consistency rate between samples. Blackstone even sells a pump to perform this type sampling. Unfortunately, not all aircraft can be sampled this way.

So to put this in the context of your quest and using your numbers:

You drain 5qts* of the 7 quarts in an engine which equates to 160 ounces of oil. Once 80 ounces of oil has drained into the waste bucket, you now take your 3 ounce oil sample to send to Blackstone.

That 3 oz sample only represents 1.8% of your 5 quarts. However, oil contamination levels are not linear, so the percentages of metal and other heavier contaminants are much higher in the first 2.5 quarts than in the last 2.5 quarts.

So for you to use Blackstone's data as a control for your hypothesis, you would need to catch all 5 quarts when drained, then send the whole 5 quarts to Blackstone for an analysis. Then get Blackstone's other customers to do the same in order to get a "fleet average." But even that still would not account for all your wear metal due to other losses. It is what it is.

* It’s closer to draining 6.5 qts than only 5 qt, but we’ll stick with your number

Good thing you weren't around when the Wrights were trying to figure out why their gliders weren't flying as well as the (incorrect) lift equation was predicting they should.

Ha. And if you were around the Wrights at that same, I can almost guarantee Charlie Taylor would have also told you your metal numbers would never add up too.

 

[AV8R_87]

I can almost guarantee Charlie Taylor would have also told you your metal numbers would never add up too.

Maybe, but I'm thinking he would've told me what he's seen in real life. And pointed out where my assumptions were wrong and how to correct them.

Your comment about stratification of metal in the oil is intriguing. I would expect that to be a factor if the oil sat for a day or more, but not that significant in the 15-30 minutes after the engine has been shut down. Most people drain the oil out of a warm engine.

Remember, this topic has started with the claim seen in multiple logbook entries stating "found no metal". A couple people pointed out that it probably meant "found nothing of concern", not "absolutely zero metal". All that back of the envelope math was trying to generate a rough estimate of how much an engine is wearing, and where does it all go, if it's not in the filter. I even took that number and reduced it by almost an order of magnitude when I posted the question, sice I knew there's a good chance real-life wear was not as high as I thought it would be.

A few people have been very hepful, pointing out some of my false assumptions, including how much metal ends in the oil or out the exhaust (completely neglected both). I now know that cylinders wear less than the 0.006" I assumed during the engine's life between overhauls.
I really appreciate their help. This is how we learn. Too bad others decided to be derrisive or worse (pretty sad to see someone state that they have better information but won't bother because I made a bad assumption due to the lack of information).

 

[chemgeek]

FYI, wear metals measured by ICP-OES or similar atomic absorption or fluorescence methods are typically less than 1 um in size, and will not be trapped by oil filter material. Nor will they be visible to the naked eye.

 

[Bell206]

I would expect that to be a factor if the oil sat for a day or more, but not that significant in the 15-30 minutes after the engine has been shut down.

Not really. For one, not all oil or contaminants are recirculated through the engine when ran. Some stay in the sump. What percentages are determined by the engine and oil system design. And there are variances.

Even in the span of 15 minutes, once the engine is shutdown, different contaminants will settle out at different rates to include starting immediately. This is one reason the best place to sample oil is from the top where the lighter particles remain in solution much longer.

Plus it’s the same reason its recommended to let half the oil quantity to drain out before a sample is taken to capture those lighter contaminants “floating” at the upper layers of the oil.

Another quirk with your metal hypothesis is the simple fact once an engine is overhauled or rebuilt it must go through an initial “run-in” phase and a “break-in” phase which can generate a lot of wear metal. Some OEMs list these phases as separate phases and some combine them in one phase.

Regardless, the “run-in” is usually performed at the OEM or repair shop on a test cell and lasts about 1-2 hours. Once done the oil is drained and systems are checked, then the books signed and the engine is shipped out, usually filled with preservation oil. So any metal shed during that initial run never reaches the end customer/owner.

The “break-in” is usually finished by the owner in the first 25 hours or so, or until the oil consumption stabilizes indicating the piston rings have seated. And this portion is usually done with straight mineral oil vs AD oil unless the engine is turbocharged in most cases.

FYI: Mineral oil does not hold oil contaminants in solution as good as AD oils so there is a tendency for those wear particles to remain in the sump at a higher percentages.

Now once the “break-in” period is finished, you would change your oil again and replace it with whatever normal oil you plan to use to include AD oils. And its only after you complete the next oil change cycle that the prevailing guidance states to start your oil analysis program.

So in short, of all the potential metal your engine could generate in wear over its lifetime, I’d SWAG at least 25% of it is shed in the first 25 hours during the run-in/break-in phases which would also never be included in Blackstone's fleet averages. So the envelop math should at least account for this loss as well.

 

[Dan Thomas]

Your comment about stratification of metal in the oil is intriguing. I would expect that to be a factor if the oil sat for a day or more, but not that significant in the 15-30 minutes after the engine has been shut down. Most people drain the oil out of a warm engine.

There is more than stratification occurring. When the drain is opened, there is some sludge real close to the drain that flows out with the first bit, which is why we don't take that first bit for a sample. The area near the drain gets cleaned of that after a while, so we take the sample. As the oil level falls, the oil at the bottom of the pan has to start moving more, and it moves some of the sludge toward the drain, so we don't sample that either.

It's instructive to watch really dirty water drain out of a sink. As the level drops you notice filth on the bottom, while the area near the drain isn't that dirty. But when the level gets low, more of the bottom junk moves toward the drain, and some never gets there at all.

So in short, of all the potential metal your engine could generate in wear over its lifetime, I’d SWAG at least 25% of it is shed in the first 25 hours during the run-in/break-in phases which would also never be included in Blackstone's fleet averages. So the envelop math should at least account for this loss as well.

Yup.

When I was in the air brake remanufacturing business, rebuilding thousands of compressors (about 17,000 of them in my 12 years there), we tested every one of them. Most of them are fed engine oil, as they have no pressure system of their own. The dyno I built had a drain sump (like a sink) under the compressor, and when the compressor was started up, you could see the gray streaks in the oil coming out of the compressor, headed for the tank, pump and filter. Those gray streaks were cast iron from the cylinder walls and rings, as the cylinder crosshatch peaks were being shaved off and the rings were similarly wearing at their tapered faces, where the lower edge wears quickly to seat to the cylinder.

I once sectioned a cylinder block after resizing it with the big rigid hone we used. I took half of that block up to the local college and used their powerful microscopes to look at the honing crosshatch. It was informative. If you've ever taken an ice-cream scoop and dragged it across the ice cream in the bucket, you might notice the torn and raised bits of ice cream left on the surface. That's what the crosshatch looked like. We started using silicon carbide ball hones to clean off the worst of that after the resizing, and it resulted in less of the light scoring of the cylinder walls on startup. The ball hone knocked that stuff off nicely, without hurting the ring seating.

Here's a much-magnified image of a honed cylinder from Total Seal Piston rings:

 

[Flyhound]

I cut open my oil filters and remove the filter paper at each oil change. I wash the filter paper with solvent in a bucket and collect the debris in the bottom of the bucket. In 2300 hours of engine run time, I never found more than a few visible flakes of ferrous metal, then, suddenly, I had just under 1/4 teaspoon of ferrous metal. I had it analyzed and the alloy matches the composition of the camshaft and the lifter bodies. My new engine will arrive later this month. Follow the service bulletin and the corrective actions it outlines!

 

[Silvaire]

Maybe, but I'm thinking he would've told me what he's seen in real life. And pointed out where my assumptions were wrong and how to correct them.

There are a lot of factors involved and your basic curiosity has merit outside of the maybe unintentional inference that somebody is lying about the whole thing. If you want to find at least some of the missing material you quest for I'd of course not suggest pouring a quart of Marvel Mystery Oil into your engine, fly it for a couple of hours and then cut open and check the filter. There are a lot of places for stuff to hide down there in the bowels of the beast and there are ways to stir the cauldron. But no, I didn't tell you to do that.

 

[Rcmutz]

I cut open my oil filters and remove the filter paper at each oil change. I wash the filter paper with solvent in a bucket and collect the debris in the bottom of the bucket. In 2300 hours of engine run time, I never found more than a few visible flakes of ferrous metal, then, suddenly, I had just under 1/4 teaspoon of ferrous metal. I had it analyzed and the alloy matches the composition of the camshaft and the lifter bodies. My new engine will arrive later this month. Follow the service bulletin and the corrective actions it outlines!

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What engine was that from? Did you have any other indications? If it was the cam lobes, was the engine making static RPM?