Is DLC the Cure for The Lycoming Achilles Heel?

MBDiagMan

MBDiagMan

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I have read and experienced the problem with the high cam Lycoming. With the cam high, if the engine is left unstarted in a humid climate for long enough, the oil can drip off the cam and corrosion will form. If the time comes when there is enough corrosion, a pit will form. Much like a chuckhole in pavement, a small piece will come out when the cam lobe wipes over it. Then another tiny particle and so on which results in metal in the oil filter, and ultimately can wipe the lobe off of the cam. This can also happen in a Continental, but I don’t think it happens nearly as frequently.

There are oil additives which keep the oil clinging to the cam and lifter. That helps. If the plane is flown regularly and/or kept in a dry climate this is often not a problem.

Roller cam followers help this problem immensely with reduced friction being a side benefit, but retrofitting to rollers at rebuild time is a pricey venture.

Lycoming is now manufacturing lifters with what is called: Diamond Like Coating (DLC.)

At this point, these lifters are very difficult to find, but fortunately I found a set for my current overhaul. An overhaul that is the result of the cam and lifter corrosion process that I described.

I don’t know how long they have been producing the DLC coated lifters, so I don’t know how tried and true they are, but it seems that this could be a major improvement.
 
Salty said:
It still won’t beat flying regularly. Engines aren’t designed to not run.
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More generically, mechanical devices like to be used by not abused.

How often do the crankshafts go bad? A camshaft is only like $800 but a crankshaft is $8000+.
 
Yes, but the case has to be split to replace either. Labor is the same. I’m not sure what point you’re making about the crankshaft vs. the camshaft.
 
Salty said:
It still won’t beat flying regularly. Engines aren’t designed to not run.
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Of course not, but things happen sometimes that prevent them from being flown. That’s the period where the DLC can be a benefit.

According to Lycon, a Lycoming distributor on the West Coast, these lifters cure the problem. I also read that Lycoming has said that if the DLC would have been available at the time they went to roller lifters, they would not have gone to the roller lifters.
 
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Corrosion and spalling of the followers is only part of the problem. In my own Lycoming history my cam looked like the surface of the moon while my followers were perfect.
 
MBDiagMan said:
Yes, but the case has to be split to replace either. Labor is the same. I’m not sure what point you’re making about the crankshaft vs. the camshaft.
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DLC is a cure for camshaft/lifters, does crankshaft have similar issues?
 
Lycoming is not the only engine manufacturer with cam and lifter problems. The stories you hear are generally the same, "this coating" or "that oil" is THE solution. Problems often still persist, although perhaps at a lower rate.

In my opinion, based on what I've seen, the engine designs with problems all have a fundamental design problem that won't be fixed by simply adding a coating or something simple. Real changes must be made, and those changes are often challenging or expensive to implement. Or in the case of aviation, type certification may limit the improvements.

I'll probably try and find a set of coated lifters to try in the next engine I do but I'm not going to expect anything amazing out of them.
 
MooneyDriver78 said:
DLC is a cure for camshaft/lifters, does crankshaft have similar issues?
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No. The cam/lifter interface is one of the most highly-loaded spots in the engine. Another is the rocker/valve interface, but it doesn't suffer the wiping effect so much. The crank and its bearings have large areas easily separated by an oil film, and those large areas will retain oil for a long time after shutdown. The loads per unit area are lower, too. Imagine that cam against the lifter: it's essentially a line with pretty much no width.

Flying regularly is the best thing for that engine. Ground-running it is the worst thing for it. Corrosion needs moisture and other contaminants, and the combustion blowby past the rings, especially when the engine isn't up to operating temps, provides vast volumes of such stuff. Flying it burns them out of the case.
 
mondtster said:
Lycoming is not the only engine manufacturer with cam and lifter problems. The stories you hear are generally the same, "this coating" or "that oil" is THE solution. Problems often still persist, although perhaps at a lower rate.

In my opinion, based on what I've seen, the engine designs with problems all have a fundamental design problem that won't be fixed by simply adding a coating or something simple. Real changes must be made, and those changes are often challenging or expensive to implement. Or in the case of aviation, type certification may limit the improvements.

I'll probably try and find a set of coated lifters to try in the next engine I do but I'm not going to expect anything amazing out of them.
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No there will not be anything amazing about them UNLESS something happens that causes the engine to set for an extended period of time. In that case, as I clearly described, the lifter will not be even remotely as likely to corrode which leads to the problem.
 
Clip4 said:
If you are buying an airplane and going to just let it sit and corrode, why are you buying an airplane?
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No one. There are people, however, that experience problems with the airplane that causes the engine not to be run for a period of time while other problems are sorted out. In the case of my plane, it had set an extended period before purchase, but they had pulled the cylinders and inspected everything so I thought it was okay. Some lessons are cheap and some are expensive.
 
MBDiagMan said:
No there will not be anything amazing about them UNLESS something happens that causes the engine to set for an extended period of time. In that case, as I clearly described, the lifter will not be even remotely as likely to corrode which leads to the problem.
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You assume the problem is corrosion. I’m not convinced. I’ve torn down numerous Lycoming engines that have sat, many in unfavorable conditions. The cams and lifters were fine.

Dan Thomas touched on what I believe is the real issue, and I believe is the primary issue in the numerous engine designs that exhibit similar cam/lifter problems. The load and wiping action between the cam and lifter is highly loaded and I believe there is insufficient area to adequately support the load. The Lycoming 76 series engines had major problems with this initially, which ultimately required modifications to the engine and required an oil additive to get by.

Lycoming has been (quietly) working on this problem for years. The coated lifters are just the latest attempt to “fix” the problem without really fixing anything. Perhaps it will work, time will tell.
 
mondtster said:
You assume the problem is corrosion. I’m not convinced. I’ve torn down numerous Lycoming engines that have sat, many in unfavorable conditions. The cams and lifters were fine.
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I have an old cam shaft that’s been sitting for 2 years on my hangar floor here in Florida with no rust. So my theory is it has more to do with how dirty the oil is as oppose to environmental conditions.
 
So do you also have the lifters on the floor next to the camshaft? The lifters are where the corrosion most often lies.

That said, yes oil neglect can most definitely exacerbate the problem.
 
MBDiagMan said:
I also read that Lycoming has said that if the DLC would have been available at the time they went to roller lifters, they would not have gone to the roller lifters.
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Curious about this. Would you have a reference or know what Lycoming's reasoning was? I thought long and hard trying to decide whether it was worth going with a Lycoming rebuild and getting the rollers or just staying with the regular lifters and an overhaul...
 
mondtster said:
You assume the problem is corrosion. I’m not convinced. I’ve torn down numerous Lycoming engines that have sat, many in unfavorable conditions. The cams and lifters were fine.

Dan Thomas touched on what I believe is the real issue, and I believe is the primary issue in the numerous engine designs that exhibit similar cam/lifter problems. The load and wiping action between the cam and lifter is highly loaded and I believe there is insufficient area to adequately support the load. The Lycoming 76 series engines had major problems with this initially, which ultimately required modifications to the engine and required an oil additive to get by.

Lycoming has been (quietly) working on this problem for years. The coated lifters are just the latest attempt to “fix” the problem without really fixing anything. Perhaps it will work, time will tell.
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ALL engines equipped with flat tappet cams have extremely high loading between cam and lifter.
 
MBDiagMan said:
ALL engines equipped with flat tappet cams have extremely high loading between cam and lifter.
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Sure. Some are higher than others though. The problem is on the marginal designs, people try all sorts of stuff to “fix” the problem. Some help but at the end of the day they still have a marginal setup.

Lycoming fixed the 76 series engines with larger diameter lifters.

Lycoming is likely not going out of their way to help owners with old engines by offering these DLC tappets. Lycoming has not made a wholesale change to roller cams and lifters, so I see this as self preservation. Further, I doubt they care much about corrosion as that would likely be viewed as neglect. It is most reasonable to assume that Lycoming is concerned about wear on cold startup, when there is little lube left on the cam and lifter surfaces, and getting the engine out of warranty reliably.

By the way, if you’d like to see where DLC on tappets didn’t work you can search for discussions on Moto Guzzi Stelvios and Grisos. The flat tappets were coated and they all fail.
 
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All it takes to keep the corrosion away is money. Lots of money. Fly daily!
 
MBDiagMan said:
ALL engines equipped with flat tappet cams have extremely high loading between cam and lifter.
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Yup, but in many other engines they're lubricated better. There's an STC'd aftermarket cam for the Lyc that has oil passages drilled through it and small exits to the cam faces. Much better than relying on oil thrown off the crankshaft.

Corrosion is the big hassle, for the most part. Once the cam and/or lifter get pitted, wear accelerates. And ground-running the thing is guaranteed to start corrosion, and not on just the cam and lifters.
 
Corrosion is not going to occur while it’s running in normal operation. I fully expect that the cam and lifters are not starved of lubrication while the engine is running. The vast majority of engines, both aircraft and automotive, operate just fine with splash onto the cam and lifters.

Additionally, oil formulated for a flat tappet engine includes a zinc additive that serves as sacrificial due to extreme pressures between cam and lifter. I have never checked, but I would be shocked if our aviation oils don’t include such an additive.
 
How is a harder DLC surface on a lifter supposed to “fix” the problem if cam lobe spalling or erosion from incipient corrosion is the issue?
 
I always enjoy the nefarious aspersions for the engine companies.
If you read what Lycoming has said, the DLC is not only harder but also more resistant to corrosion. Will it solve all problems, I doubt it. Will it make the engines better, likely.

Also, why does almost everyone forget that almost all engines have not only hours but also calendar TBO? It is for this reason.

Tim

Sent from my HD1907 using Tapatalk
 
455 Bravo Uniform said:
How is a harder DLC surface on a lifter supposed to “fix” the problem if cam lobe spalling or erosion from incipient corrosion is the issue?
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The coating is not there for anti wear purposes. It is there because of its anti corrosion properties. I thought I was clear in my original post. I will go check it.
 
455 Bravo Uniform said:
How is a harder DLC surface on a lifter supposed to “fix” the problem if cam lobe spalling or erosion from incipient corrosion is the issue?
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I thought the spalling lifters then cause the cam to wear, instead of a smooth surface, it’s more like sandpaper?
Less friction and no spalling reduces cam wear.
 
That’s correct! Spalling usually begins from corrosion making a tiny crater that begins chipping out like a Chuck hole leading to metal in the filter and spalling of the lifter. In extreme cases the spalled lifter wears down the cam lobe.
 
As far as splash lubrication goes, in many engines of all types, if you were to put a see through window on the case and observe while running it would look as if someone were in there with a pressure washer.
 
tspear said:
I always enjoy the nefarious aspersions for the engine companies.
If you read what Lycoming has said, the DLC is not only harder but also more resistant to corrosion. Will it solve all problems, I doubt it. Will it make the engines better, likely.

Also, why does almost everyone forget that almost all engines have not only hours but also calendar TBO? It is for this reason.

Tim

Sent from my HD1907 using Tapatalk
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Yeah, it sorta drives me nuts that people disparage a 50 year old lycoming (that’s only run 75 hours a year and most of that the first 10 years of its life) for being susceptible to corrosion.

You take your “bulletproof” car engine and sit it in a garage for 50 years and do nothing to it and it won’t be so bulletproof either.
 
MBDiagMan said:
As far as splash lubrication goes, in many engines of all types, if you were to put a see through window on the case and observe while running it would look as if someone were in there with a pressure washer.
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Wait till people learn about dipper motors and poured babbit bearings. Engines can run with much less technology that you think. Even the most modest amout of lube is better than nothing.
 
MooneyDriver78 said:
I have an old cam shaft that’s been sitting for 2 years on my hangar floor here in Florida with no rust.
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Could stress corrosion be a factor here? It seems to me that the cam and lifter will be subject to approximately the same high stresses when static at a high valve lift as they see when running.

The cam forces the valve open and the spring forces it closed. The two forces must be similar since the valve motion is similar in the opening and closing phases.

Maybe there is an engine position that minimizes the valve lifts when static? Well for a 4 cyl, not much chance in the case of a 6:) I doubt there is one for a 4 either.

https://www.materials.unsw.edu.au/s...ls/corrosion/types-corrosion/stress-corrosion
 
MBDiagMan said:
Additionally, oil formulated for a flat tappet engine includes a zinc additive that serves as sacrificial due to extreme pressures between cam and lifter. I have never checked, but I would be shocked if our aviation oils don’t include such an additive.
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No zinc in aircraft oils.

When ashless dispersant oils were introduced for auto engines, they were also suitable for aircraft engines and eventually were adopted for aviation use.However, when zinc antiwear and metallic detergents were formulated into auto oils, an important divergence occurred. Aircraft engines burn a fair amount of oil and, if these metal-containing detergents and antiwear compounds are present, they can form metallic ash deposits in the combustion chambers. These deposits can lead to destructive preignition, which could burn holes in the tops of pistons with obvious catastrophic results. For that reason, it was decided that aviation oils were to remain ashless to avoid the risk of metallic deposits.

From https://www.avweb.com/ownership/oil-myths-debunked/
 
I read a long report on the Lycoming valve system history and how each fix presented new issues. IRC, the issue started at the initial design, with where the cam is located and how it is lubed and how oil gets from there to the rest of the valve train.
It was an interesting read. The Skyranch Engineering Manual has lots to say kn the subject too.
 
This could be a stupid question however I'm going to ask it

Desmodromic valves have been in use since the late 1860s and are often cited as one of the more successful elements of Ducati motorcycles..

Outside of the simplicity of pushrods is there any reason other methods weren't explored? As I understand it the stresses of a desmodromic valve are much lower. It's not "new" tech, I want to say they've been in production use since the early 1950s..?

n00b
 
Tantalum said:
Desmodromic valves have been in use since the late 1860s and are often cited as one of the more successful elements of Ducati motorcycles..

Outside of the simplicity of pushrods is there any reason other methods weren't explored?
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Is this in relation to aircraft engines? As I understand it, desmodromic valves were developed in response to problems encountered at high RPM, which is nowhere near the region our Lyco/Conti engines run.
 
asicer said:
Is this in relation to aircraft engines? As I understand it, desmodromic valves were developed in response to problems encountered at high RPM, which is nowhere near the region our Lyco/Conti engines run.
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Correct but if wiping stresses are a factor pertaining to this thread perhaps it might help there? I believe it's a much smoother overall operation with lower stress. Hell, they give dogs (female too) with certain heart conditions generic Viagra

Doesn't really matter, I was just curious if it had ever been tried or there's some reason it wouldn't work.. (desmodromic valves)
 
Cam and tappet spalling is the result of subsurface cracks that develop as a result of extreme loading under pressure. Corrosion can lead to spalling but corrosion is not the principle cause — plastic deformation of the lifter and cam surfaces under pressure is the cause

A key factor in spalling is oil viscosity. Multiweight oils have a lower base viscosity, which may encourage spalling during engine start where a fixed weight oil would provide better protection

on the other end of the equation, multiweight oils may provide better protection at operating temperature where their viscosity enhancers allow a higher viscosity at higher temperatures — multiweights don’t thin out like straight weights at high temps

I run Philips 25W-60 in my O-360 and have had very good luck
 
If you believe corrosion to be a factor with Cam Life an Engine Dryer

may be a thought.

I’ve had few comparisons of engines with/without the system.

Time SMOH both operating and calendar were similar we were

frequency of flight and storage conditions.

These were evaluated “ jugs off”.

On one engine jugs went back on and the other all were replaced due to rust.

Fortunately the Cam was fine on both.

Dryers are available to buy or you can “ roll your own” with an aquarium pump

and a jar of dessicant.
 
nitpick said:
Cam and tappet spalling is the result of subsurface cracks that develop as a result of extreme loading under pressure. Corrosion can lead to spalling but corrosion is not the principle cause — plastic deformation of the lifter and cam surfaces under pressure is the cause

A key factor in spalling is oil viscosity. Multiweight oils have a lower base viscosity, which may encourage spalling during engine start where a fixed weight oil would provide better protection

on the other end of the equation, multiweight oils may provide better protection at operating temperature where their viscosity enhancers allow a higher viscosity at higher temperatures — multiweights don’t thin out like straight weights at high temps

I run Philips 25W-60 in my O-360 and have had very good luck
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Your statements about oils disagree with everything I have every read. Multi-weight oils are thinner at lower temps, especially compared to single weight oils; they are designed this way to facilitate startup of the engine.

Tim
 
I ran numerous Lycomings, for thousands of hours each, exclusively on Aeroshell 15W50, and never once had cam issues. That oil has the Lycoming LW-16702 anti-scuffing additive in it, the stuff specified by the AD on the O-320-H2AD engines. It is slippery stuff. In my ancient A-65 it dropped the oil temp by 25 or 30 degrees. It reduced the friction considerably. That's what you need in that cam/lifter interface.
 
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