do we see corrosion damage in the oil filter?

[KayS]

Hey there, we had a discussion recently about engine internal corrosion and the question if we can see the damage caused by it in the filter element.

opinion 1: corrosion nibbles at the hardened surface of a cam lobe for example. that results in further damage by wear and small metal chips will be produced that are shiny enough to be visible after cutting the filter.

opinion 2: corrosion eats through the surface slowly and the sacrificed material is too rusty (not shiny enough) to be visible in the filter element. one does his frequent filter inspections, sees no metal and thinks "all good". but it's not.

what do you think? 1 or 2 or is there a 3?

you all have a great day
Kay

 

[rv8ch]

Hey there, we had a discussion recently about engine internal corrosion and the question if we can see the damage caused by it in the filter element.

opinion 1: corrosion nibbles at the hardened surface of a cam lobe for example. that results in further damage by wear and small metal chips will be produced that are shiny enough to be visible after cutting the filter.

opinion 2: corrosion eats through the surface slowly and the sacrificed material is too rusty (not shiny enough) to be visible in the filter element. one does his frequent filter inspections, sees no metal and thinks "all good". but it's not.

what do you think? 1 or 2 or is there a 3?

you all have a great day
Kay

Hi Kay, I'd say there is an option 3 - oil analysis. Rust will show up in a good oil analysis as Iron (Fe).

Oil analysis is not expensive, but is kind of a hassle. However, if it's done consistently, it will probably help identify issues early enough to avoid catastrophic engine failure in some cases.

From what I understand, rust alone will not cause engine failure, but performance problems. Cam lobes will wear, and this decreases power. Cylinder wall rust will just scrape off, and slowly decrease performance.

Best ways to avoid rust are to fly often, use camguard, use an engine dryer, keep your aircraft in a very dry climate like in Andalusia or the Mojave.

 

[MacCool]

Examining the oil filter is useful but if your engine is circulating chunks that big then you are way behind the curve and catastrophe is looming. Much more useful in indicating ongoing engine wear IMHO is trending in oil analysis. My A&P dissects the oil filter, checks the oil screen, borescopes, and sends a sample to Blackstone every time.

As to prophylaxis, my engine is on a dehydrator 24/7/365, and although skeptical of its value, I do use Camguard on a probably-won't-hurt/might-help basis.

 

[airguy]

Corrosion, by definition, is putting metal into solution with the oil on a molecular level - far too small to be found in the filter. You need an oil analysis for that.

Now if corrosion goes far enough to cause large chunks of metal (relatively large, in the microscopic realm) to break off and float into the oil, those will be caught in the filter to see - but that was an effect of the corrosion already in an advanced state, not a direct detection of the corrosion itself.

 

[DanH]

Like Greg said, it depends on the size of the chunks...

 

[PCHunt]

In addition to the above, I rub a small magnet over all of the filter element surface after spreading it out to inspect.

 

[KayS]

Thank you all for the inputs!

i will check the oil analysis option. over the past years i collected all oil samples after each oil change but didn't send them to a laboratory. will check with blackstone if it makes sense to analyze these old oil samples.

btw... i found an crash report from the accident investigation board of switzerland. swiss a are known to be kinda slow but thoroughly:

https://www.sust.admin.ch/inhalte/AV-berichte/2160_e.pdf

the report indicates corrosion on the cam lobes/tappets as the root cause for three fatal. interesting pictures on page 21 - 23.

i find it somewhat odd that we have so little tools on hand to assess the corrosion condition of our engines. considering the gravity of the topic in regard to safety and costs.

 

[Dan 57]

found an crash report from the accident investigation board of switzerland. swiss a are known to be kinda slow but thoroughly

Not sure what the Swiss are, or are not, but the reference accident happened 26 August 2010, the SUST enquiry board finished it's report 4 December 2012, and it was approved and published on 10 January 2013.

The above mentioned accident triggered the introduction of a nationwide engine inspection program at the time, as well as the introduction of supplemental on condition maintenance programs for any engine operated above the TBO or time interval recommendations as published by the manufacturers.

Re oil analysis, remember that this will detect a lot of other possible problems with your engine, and I consider this step as a safety mandatory measure to be performed at least every 100h/once a year, whichever comes first.
Not sure sending your old (how old?) samples is worth the effort, but yes for future ones.

Anti-corrosion measure... as advocated by the manufactures themselves, GO & FLY. Once a week for more than 1 hour is the absolute minimum to try to prevent corrosion in an engine.
There are additional measures, such as engine dryer, oil change not only based on hours but also time intervals, etc, but nothing beats a good flight

 

[KayS]

Dan, where i live switzerland is very close. almost within walking distance and sometimes we can't restrain ourself commenting on the neighbours. i'm sure it's vice versa.

the report shows that the size of the lobes have been reduced by corrosion that lead to an decreased intake valve lift. this resulted in less fuel/air mix entering the cylinder and therefor less power.

the report also assumes that this happened over longer period of time and the pilot didn't notice it.

i wonder if we can detect these kind of problems if we do a max power/speed test. if the speed is smaller than the number we noted during initial flight test phase then this could indicate a problem. stupid idea?

 

[Dan 57]

a max power/speed test. if the speed is less than we noted during initial flight test phase then this could indicate a problem

If one could perform such a test flight under the exact same conditions and configuration, and a decrease of real performance is observed, the existence of a loss of power would be validated.
The same test flight resulting in no performance loss would prove... nothing re corrosion (or the pitting or galling of the camshaft as in the cited in the accident mentioned above) either. One could well equal initial performance with an engine suffering any kind of damage, but still in the initial phase.

Regular oil analysis will show developing engine damage such as the one cited above.

Now if you are worried about your camshaft and its lobes, there are ways of inspection such as visually looking at them (borescope or directly), or measuring individual pushrod travel for instance.

 

[lr172]

Dan, where i live switzerland is very close. almost within walking distance and sometimes we can't restrain ourself commenting on the neighbours. i'm sure it's vice versa.

the report shows that the size of the lobes have been reduced by corrosion that lead to an decreased intake valve lift. this resulted in less fuel/air mix entering the cylinder and therefor less power.

the report also assumes that this happened over longer period of time and the pilot didn't notice it.

i wonder if we can detect these kind of problems if we do a max power/speed test. if the speed is smaller than the number we noted during initial flight test phase then this could indicate a problem. stupid idea?

It would take years for corossion to eat away a cam lobe. Typically, the lifter face gets some corossion that creates very small divots in the steel (i.e. pitting). This is a high load interface with the cam lobe. Any imperfections, like these divots, will cause the area around the divots to be worn away slowly by the cam lobe. This gets worse and worse and once bad enough, starts to cause wear on the cam lobe. This can go on for some time. Once it gets bad enough it snow balls and the lobe quickly wears away.

So, corossion gets it all started, but wear is the primary means of destruction for the cam lobe.

Pretty easy to test for shrinking lobes. You can pull the rocker cover and place a dial indicator on the valve spring retainer and roatate the crank. Multiply valve movement by the rocker ratio and compare to cam's lift spec. Intake and exh are likely different. Unsure if Lyc publishes this data, but sure it is out there somewhere.

 

[rv8ch]

If one could perform such a test flight under the exact same conditions and configuration, and a decrease of real performance is observed, the existence of a loss of power would be validated.
The same test flight resulting in no performance loss would prove... nothing re corrosion (or the pitting or galling of the camshaft as in the cited in the accident mentioned above) either. One could well equal initial performance with an engine suffering any kind of damage, but still in the initial phase.
...

If you have an engine monitor and save the files, pretty soon software analysis will be able to detect things like power changes at the same or similar conditions. Most engine monitoring keep track of all the data needed to know if the engine is losing power. This will come from either Savvy or one of their competitors.

Can't agree more with fly often, regular oil/filter changes, engine oil analysis, camguard, and an engine dryer as ways to extend the useful life of your engine.

 

[tgmillso]

Another thing to avoid if you want to minimize the risks of corrosion, is leaded fuel. Here is an excerpt from the CAA Pilot's Power Plant Manual. It is amazing the depth of knowledge that was present in 1940 on this topic.

Tom.
RV-7, that doesn't drink leaded fuel.

https://books.googleusercontent.com...ErpIiOtrmly3jxicZRZQdli7NMF_m6Qg4CrjwpYCMH0Vg


PAGE 194
TETRAETHYL LEAD
A convenient means of improving the antiknock characteristics of a fuel is to add a knock inhibitor. Such a fluid must have a minimum of corrosive or other undesirable qualities and probably the best available inhibitor in general use at present is known as tetraethyl lead . The few difficulties encountered due to corrosion tendencies of ethylized gasoline are insignificant compared with the results obtained from the high antiknock value of the fuel.
....
Ethyl fluid, in addition to tetraethyl lead and a trace of dye, contains sufficient ethylene dibromide to convert the lead to lead bromide, which is volatile at exhaust temperatures and so passes out of the engine with the exhaust gases. Without the use of ethylene dibromide, the lead would be deposited in the engine as lead oxide, which, in addition to building up a deposit, would cause considerable corrosion. Lead bromide at high temperature is also an extraordinarily highly corrosive
compound.
...
The addition of more lead than is required to eliminate detonation has the effect of decreasing the power slightly and increasing the temperature of the exhaust gases.

Corrosion due to ethyl gasoline.-There are two distinct types of corrosion due to ethyl gasoline. The first is caused by the reaction of the lead bromide with hot metallic surfaces, and occurs only when the engine is in operation. The second is caused by the condensed aqueous products of combustion ,
chiefly hydrobromic acid, when the engine is shut-down. The various parts of an engine most affected by corrosion and preventative measures are discussed in the following:
Steel cylinder barrels in composite steel-aluminum cylinders corrode
rapidly due to galvanic action with aluminum bromide. Corrosion due to condensed aqueous products of combustion can be eliminated by injecting oil or more effective rust-preventive compounds into the intake ports as near the valve as possible on stopping the engine.
Valves and valve-seat inserts do not present corrosion difficulties to any great extent when the valve gear is lubricated properly. The cooling of the exhaust valves by means of sodium reduces high temperature corrosion. Austenitic nickel-chromium valve steel nearly eliminates valve corrosion. Stellited valve faces and valve-seat inserts show practically no attack from use of ethyl gasoline.
Exhaust disposal systems have been the cause of airplanes burning up while the engines were idling or had just been shut-off, due to hot iron oxide flaking off the exhausts. The oxide deposit probably is caused by the action of hot lead bromide on the exhaust steel. This problem has been solved by the use of stainless steel for exhausts. Camshafts, rocker arms, valve springs , etc., are subject to a certain amount of corrosion. This may be eliminated by providing more lubrication , since
corrosion of metal does not occur when the metal is covered with a film of oil .
Other means of reducing it are by avoiding overcooling, and the presence of
pockets in the valve gear and means of removing the fumes, thereby reducing
the amount of aqueous condensation.

 

[KayS]

Tom, interesting article, thank you. never heard about that. is this related to the acid by-products formed by combustion and that end up in one form or another in the oil? maybe another plus point for reducing the use of leaded fuel.

 

[Mconner7]

What a failing cam looks like

Here is my 540 after 800 hours since overhaul, about 10 years time.

 

[Mconner7]

There was almost no metal on the oil filter or suction screen and analysis said it needs to be run more often…

 

[wcalvert]

Those are some great pics of cam/lifter wear and fatal damage!

I've seen some seriously abused auto engines that didn't show that kind of destruction for thousands of miles (100's of thousands). Run out of oil from a punctured oil pan (off road) and continued on after a repair. Or engines sitting idle for years and started up with no lasting damage (pump equipment). Engines with the crankcase full of fuel from a ruptured fuel pump (mechanical auto pump) that trucked on for years.

My question is why these aircraft engines seem to be so dang delicate? Are the loads on these internal parts so high that they are intolerant of any operations out of the normal? Local temperatures at wear points super high? Poor materials?

There is definitely a list of things these engine like and don't like, but they sure seem dainty.

Inquiring minds want to know!

 

[Dan 57]

Poor materials?

Can't prove anything myself, but probably a good guess. The cheapest chinese steel is more corrosion prone than the more expensive one.

Besides, these engines being real cheap and hi tech to start with, don't expect any better quality.

 

[rv8ch]

Those are some great pics of cam/lifter wear and fatal damage!

I've seen some seriously abused auto engines that didn't show that kind of destruction for thousands of miles (100's of thousands). Run out of oil from a punctured oil pan (off road) and continued on after a repair. Or engines sitting idle for years and started up with no lasting damage (pump equipment). Engines with the crankcase full of fuel from a ruptured fuel pump (mechanical auto pump) that trucked on for years.

My question is why these aircraft engines seem to be so dang delicate? Are the loads on these internal parts so high that they are intolerant of any operations out of the normal? Local temperatures at wear points super high? Poor materials?

There is definitely a list of things these engine like and don't like, but they sure seem dainty.

Inquiring minds want to know!

This is a great question. From what I've read, and many discussions with many experts - many on this forum - the major differences are:

• we don't fly as often as we drive
• water cooling
• unleaded fuel
• higher quality manufacturing driven by Mr. Deming's work after WWII

Most people have seen aviation engines go 1000s of hours past TBO if they are flown regularly. I think everyone has seen a car engine that's gone over 3000 hours (100,000 miles). We've also seen car engines with problems, at least those of us over 50 have.

 

[KayS]

Bill: these tappets can't be poor material. Spruce sells them for 264 bucks each.

Mconner: thank you for these great pictures. it's interesting that you didn't notice significant metal.

Would be roller tappets better in this regard?

 

[BillL]

Yes

Would be roller tappets better in this regard?

Much better. The cam contact zone of the follower is a high contact stress area, and rolling is better than sliding. There is some boundary lubrication and corrosion is like a grooved runaway, it removes any hydrodynamic films.

It is not just lead in the post combustion gasses, it contains sulfur oxide from the sulfur in the fuel. That dissolves in water (a primary by product of combustion) and then condenses inside the crankcase. It is the sulfur, not pure H2O that promotes corrosion. Water becomes conductive with ions (sulfur) and then corrosion occurs. In spite of marketing color plots of ambient humidity - it is irrelevant to the crankcase.

If one gets highly technical, the lubrication engineers will call lack of a hydrodynamic film "boundary lubrication" like on highly loaded and slow moving gears. Look up 4 ball testing if you want to know more.

Edit: Slipper follower cams are far less durable than roller followers both being good quality. I needed a new cam in my '77 chevy 350 every 80 k miles. All GM V8's adopted roller followers in the the mid 80's when the EPA required a 100,000 mile durability test for emissions - the cams would not last. Aircraft cams are hardened steel, which is about the best for that design, so would not say poor design or material specifications/selection, but it certainly is not tolerant of misuse i.e. corrosion.

 

[tgmillso]

To Bill and Kay,

I will preface this with the fact that I'm an engineer not a chemist, but basically ethyl bromide is added to leaded fuels in order to scavenge the lead that when pushed as blow-by into the crankcase would otherwise buildup in oil galleys and starve the main bearings of oil. The problem is that this ethyl bromide combining with the lead forms a metal and a non metal, i.e. a salt. This Lead (II) Bromide salt then causes any water (again a result from blow-by of combustion gasses into the crankcase) to become very electrically conductive. The higher the conductivity of the moisture in the crankcase, the faster the reaction can occur with the iron (Fe) and the available oxygen. Remove the salt, and you drastically reduce conductivity of the water, which subsequently reduces the reaction rate between the iron and oxygen.
We still get moisture blow-by and oxygen in the crankcase of car engines, but we don't run lead anymore, so we're not stressing all the time that the car engines are going to corrode if they are not run weekly to re-coat the steel surfaces with a layer of oil to protect them from corrosion.
If you haven't read it already, here is some good info on running unleaded fuels:
https://www.avweb.com/features/pelicans-perch-55lead-in-the-hogwash/

You should probably also read this if you are not running LOP:
https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/

If your engine is a 8.5:1 CR or below, transition to unleaded fuels is rather simple. At higher CR, this is still possible, but you may need to adjust timing:

https://www.lycoming.com/content/un...ed automotive gasoline,out in a press release.
https://www.lycoming.com/sites/default/files/attachments/SI1070AB%20Specified%20Fuels.pdf

The main thing to watch when running mogas is that the RVP (Reid Vapor Pressure) isn't as good as AVGAS, so it is more likely to boil/vapor lock. This means that you need to make sure you haven't got elements in your fuel system that are making this situation worse, for example:
- Tight 90° bends prior to the mechanical fuel pump. Tight bends increase the flow resistance, which means the mechanical fuel pump has to suck harder, increasing the risk of vaporization.
- Unnecessarily high oil temperatures caused by undersized oil coolers or poor airflow. The mechanical diaphragm fuel pump is essentially the temperature of the crankcase, as it is bolted to the back of it. If the mechanical fuel pump is super hot when sucking fuel into it, then there is the risk that the fuel boils off and cannot be drawn into the pump.
- Your fuel tanks are not painted a dark color, so the fuel doesn't get heat soaked on the ground. The hotter the fuel, the higher the boiling/vaporization risk when it is sucked by the fuel pump.
- Fuel likes in the engine compartment are shielded against radiant heat from the exhaust and are insulated (which should be the case anyway).
- You don't use winter blended mogas, as it has a higher (bad) RVP.
- Your electric boost pump is in good working order. This pump is low down and enables you to positively pressurize the fuel system in the case where you do have a vapor lock issue, and will enable you to keep the engine running until you can get to the root cause of why the mechanical fuel pump is not able to draw fuel by itself.

To reduce your crankcase component corrosion risk further, you can run a engine dehumidifier, as seen at the bottom of the following page:
https://vansairforce.net/community/showthread.php?t=157922

There are plenty of other benefits of running unleaded fuel. It is less toxic than leaded fuels, typically 30% less expensive in most situations, results in less valve buildup that leaded fuels, and stops us giving the public yet another reason to hate small aircraft.

Cheers,

Tom.
RV-7