Picture of Lifters, Flat, DLC, Roller

[jetdriven]

Idk but the engine builder at Lycon has ran some DLC lifters through 3 TBO cycles on some traffic watch planes.   That’s 6000 hours.   Still going.  

[N201MKTurbo]

31 minutes ago, jetdriven said:

Idk but the engine builder at Lycon has ran some DLC lifters through 3 TBO cycles on some traffic watch planes.   That’s 6000 hours.   Still going.  

Those engines had to run a lot! DLC hasn’t been around for all that long. Engines that are ran that often do well with whatever they put in them. I would be more impressed with a 30 year old engine making it to TBO with no cam or lifter wear.

I’m not anti DLC, in our application the additional cost is insignificant. It is not a cure all.

At work, we had a project with a highly loaded lead screw. The threads kept failing. I suggested they have the screw and nut DLC coated. We did, it gave about a 1% increase in load before the threads failed. We tried other anti-friction coatings as well, none of them worked. The solution was old school. (It’s proprietary)

[jetdriven]

Well, it’s the only flat lifter solution that appears to be working. I’m gonna throw this out this like roller lifters, I have yet to see one spalled yet.  I have heard of hundreds of cases of spalled flat lifters. 
I don’t think the DLC coating  is to lower friction. It is to keep the lifter face clean and corrosion free, and smooth. That way it can’t develop pits which turn into scoring which turns into cam scoring which turns into lifter spalling and a new engine. 

[Hank]

1 hour ago, N201MKTurbo said:

At work, we had a project with a highly loaded lead screw. The threads kept failing. I suggested they have the screw and nut DLC coated. We did, it gave about a 1% increase in load before the threads failed. We tried other anti-friction coatings as well, none of them worked. The solution was old school. (It’s proprietary)

Several jobs ago, we had long knives that cut tyvek rolls to seal large trays (12" wide) for sterilization, and had to frequently resharpen the blades. Tried lots of coatings, various heat treating cycles, nothing helped. Then we tried diamond black, half a thousandth thick (0.0005"), and went from several weeks to almost a year between sharpenings. Used in in several other applications after that, with similar results. It's good stuff! I still remember shipping parts to Conover, NC.

[Guest]

2 hours ago, N201MKTurbo said:

Those engines had to run a lot! DLC hasn’t been around for all that long. Engines that are ran that often do well with whatever they put in them. I would be more impressed with a 30 year old engine making it to TBO with no cam or lifter wear.

I’m not anti DLC, in our application the additional cost is insignificant. It is not a cure all.

At work, we had a project with a highly loaded lead screw. The threads kept failing. I suggested they have the screw and nut DLC coated. We did, it gave about a 1% increase in load before the threads failed. We tried other anti-friction coatings as well, none of them worked. The solution was old school. (It’s proprietary)

I’ll bite, clean grease?

Clarence

[N201MKTurbo]

36 minutes ago, Hank said:

Several jobs ago, we had long knives that cut tyvek rolls to seal large trays (12" wide) for sterilization, and had to frequently resharpen the blades. Tried lots of coatings, various heat treating cycles, nothing helped. Then we tried diamond black, half a thousandth thick (0.0005"), and went from several weeks to almost a year between sharpenings. Used in in several other applications after that, with similar results. It's good stuff! I still remember shipping parts to Conover, NC.

Yes, I’ve seen quite a few surgical tools that have DLC. It seems to do wonders for blades. As long as you never want to sharpen them...

[N201MKTurbo]

4 minutes ago, M20Doc said:

I’ll bite, clean grease?

Clarence

The grease was part of it. It was clean room, so it limits your choices. Mostly the right materials and thread profile. The solution was not intuitive.

 

[Raptor05121]

3 hours ago, N201MKTurbo said:

Those engines had to run a lot!

30% of the GA fleet accounts for 70% of fleet use. AKA commercial ops. I do survey in 172s and we each fly 6-8 hours a day, nonstop. With 6 planes in our little fleet the FBO is loving us burning almost 500 gallons a day. The owners have an engine sitting on a crate in the hangar waiting for the first plane to "pop".

I saw a post on FB last week, guy had the highest time Cessna 172 in the world- some 70,000 hours since new doing fish spotting off the Maine coast. I think he said he went through 25-30 engines

[bradp]

I’ve seen some hot rod and classic car folks decry DLC coatings (when not if it fails) like it will eat the cam- different metallurgy of those fans not polished steel? I too would love to see some data for age vs hrs.  Commercial flight ops flying 2000 hrs in a year or two isn’t reflective of any/most of us here. 

[corn_flake]

Interesting discussion.  The engine rebuild shop guy (Lycon) was telling me that lifter spalling will no longer be a problem even if I let the engine sit for extended period of time.  This would imply the DLC coating have some sort anti-corrosion property.  

[carusoam]

Keeping corrosion from happening...

Takes removing any of the two team mates... oxygen or moisture...

The DLC coating probably keeps any molecules from getting to the metal surface under it...

moisture is the enabler for oxygen to do the dirty work....

DLC seems to be a coating strong enough to stay in place...and tight enough to keep oxygen from getting through...

Trying to Get a coating to stick is a challenge....

Having one be hard enough to not wear is  another challenge...

Having one that is smooth enough and keep oil attached it... is icing on the cake...

If the surface cracks any... the oxygen will get under it, the corrosion starts, rust particles expand in volume, lifting more of the coating off... a terrible cycle to begin...
 

As long as oil stays between the surfaces... it doesn’t matter which part is harder than the other... they only wear if they are in contact with each other...

The wear issues have been superseded by the corrosion issues... prevent corrosion, to prevent spalling...

PP thoughts only, not a mechanic...

Best regards,

-a-

[jetdriven]

On 5/25/2020 at 6:06 PM, corn_flake said:

Interesting discussion.  The engine rebuild shop guy (Lycon) was telling me that lifter spalling will no longer be a problem even if I let the engine sit for extended period of time.  This would imply the DLC coating have some sort anti-corrosion property.  

Yes, it cant corrode.

[RobertGary1]

On 5/20/2020 at 6:22 AM, N201MKTurbo said:

I wonder what the time in service was for the three lifters in the picture? The DLC and roller lifters can't be more than a few years old, the one on the left could have been in service sense the 60s.

My thoughts too. 

[jetdriven]

1 hour ago, RobertGary1 said:

My thoughts too. 

that rust isnt from the 60's.  its recent.  Aviation Consumer did a test a few years ago, they set lifters out after being dunked in oil, and they would have a bright bloom of corrosion on them after three days.. The Camguard ones would do a little bit better, they would go 2 weeks. I think it was a different article, but the ones put inside of a box that was fed dry air from a desiccant dryer went a whole month with no visible change

[201Steve]

4 hours ago, jetdriven said:

inside of a box that was fed dry air from a desiccant dryer went a whole month with no visible change

I want to design an inflatable whole-airplane cover that dehumidifies the air inside of it. 

[larrynimmo]

6 hours ago, 201Steve said:

I want to design an inflatable whole-airplane cover that dehumidifies the air inside of it. 

Basically humidity is driven by physics....for example, if you add a little heat to the cabin...it will stay above the dew point and all electronics will stay dry as well as upholstery, insulation and even the associated skins of the plane.

as for the engine... I put a small explosion proof heater through the pilots side cowl opening on top of cylinder #2 with a blanket over entire cowling.....placement of this heater  keeps the top end of the engine cozy....the coldest part of the engine is the oil sump...any condensation that would likely occur would be on the surface of the oil....this water would be quickly dissipated  once in operation after oil heats to 180 degrees.

even with my approach, when 100%RH  occurs, the wings get wet inside and out 

 

 

[201Steve]

Something like this, here are two examples from the auto world. 

[carusoam]

Use caution with the bubble idea...

They are great for positive pressure...

Even dust free when using filtered air...

Check to see if they are using a dehumidifier in there anywhere...

Dehumidifying doesn’t use a lot of science...

But, it needs some...

There are many ways to measure and record RH as well...

So... use some science... surround your important machine parts with dry air... use a measuring and recording device to make sure you get what you are looking for...

 

I can’t imagine the effort required to park a car inside the bubble... I bet it gets used twice...

Clean room engineering thoughts only, not just a PP...   

Best regards,

-a-

[ArtVandelay]

that rust isnt from the 60's.  its recent.  Aviation Consumer did a test a few years ago, they set lifters out after being dunked in oil, and they would have a bright bloom of corrosion on them after three days.. The Camguard ones would do a little bit better, they would go 2 weeks. I think it was a different article, but the ones put inside of a box that was fed dry air from a desiccant dryer went a whole month with no visible change

My old cam (1996) has been sitting on the floor in my hangar (in Florida, only a couple of miles from the ocean) for 3 years....with no appreciable rust, with no oil, no camguard. Maybe lifters are made of a different alloy, but the cam doesn’t rust easily.


Tom

[carusoam]

The big problem...

The cam followers suffer from inter-granular type corrosion...

it looks like whole granules of metal fall out at the surface...  leaving pock marks with sharp edges...

The oil film is unable to lubricate the pocked surface...

The cam lobe machining begins after that...

I’m not sure if rusting through the hardened layer of the cam lobes is required... or if the pocked followers are such a good cutting tool... they start on the hardened layer until they are cutting through the soft heart of the lobe...

PP thoughts only, not a metallurgist...

Best regards,

-a-

[Old Chub]

Well actually no.

"The cam followers suffer from inter-granular type corrosion..."   

The "pock marks" you are referring to found on the face of the lifter face are caused by spalling which is a subsurface fatigue failure mode.   Inter-granular corrosion can be found in several other types of failures to include stress corrosion cracking, hydrogen embrittlement and other but is a complete different than the spalling that is commonly found on the face of the lifter.   

7years as a metallurgist at an aerospace company in the Field Investigations Lab.

 

 

[carusoam]

I’ve been schooled! 
 

OC,

Thanks for the kind sharing of details...

I didn’t get enough metallurgy in my one materials class... and lab...

I have seen the word spalling used to describe this failure... but failed to recognize the details...

 

It does open up a few more questions, if you have time...

 

1) What are the causes of the spalling on some lifters... lack of oil?

2) Is the lunar landscape that is caused by spalling... whole granules falling out?

3) we see damaged cams... and often rust gets blamed for their demise...

4) it is looking more like... whenever a cam lobe goes away... there is a lunar landscape on the adjoining cam follower...

5) Does a DLC coated cam follower avoid the issues that can cause the spalling?

Thanks again for sharing the great details!

Go MS!

PP thoughts only, not a mechanic...

Best regards,

-a-

[PT20J]

On 1/27/2021 at 7:30 PM, Old Chub said:

Well actually no.

"The cam followers suffer from inter-granular type corrosion..."   

The "pock marks" you are referring to found on the face of the lifter face are caused by spalling which is a subsurface fatigue failure mode.   Inter-granular corrosion can be found in several other types of failures to include stress corrosion cracking, hydrogen embrittlement and other but is a complete different than the spalling that is commonly found on the face of the lifter.   

7years as a metallurgist at an aerospace company in the Field Investigations Lab.

 

 

We know a few things about cam/lifter failures:

1. Lycoming aircraft engines seem to suffer these failures more often than other engines (at least before the advent of coated lifters and roller lifters).

2. From observation, it appears that the lifters fail first and damage the camshaft.

3. The primary failure seems to be spalling probably due to rolling contact fatigue.

There is a lot of supposition in the popular literature that corrosion precipitates or accelerates the spalling. The prescribed antidote is to fly often and avoid short flights which presumably might increase the combustion products (due to blowby) and water vapor (from combustion and blowby) in the crankcase thus providing an environment favorable for atmospheric corrosion. But there are certainly reported cases of airplanes flown regularly that still have cam/lifter distress. And, I have not found any definitive data that show that corrosion is any more significant in aircraft camshafts and lifters than it is automobile engines which seem to run forever.

So, I'm wondering if we are giving too much weight to an unproven corrosion hypothesis when the problem isn't actually a design/metallurgy issue.

Any thoughts?

Skip

[larrynimmo]

When we speak about automotive engines, typically they run under 2,000 rpm with less than 12% of the available horsepower....with a very clean lead free gasoline preserving good oil lubricating properties.  Aviation engines typically cruise 2300-2600 rpms at 55%-75% power adding operating stresses in addition to running oil that has been degraded by lead pollution.   Added to that our planes can sit unused for months unlike most cars.

according to my AI, most flight school engines (with 100 hr inspections and oil changes) go TBO without engine issues....fly often and many hours a year should help to get 2,000 hrs from an engine.   I have read that Lycomming has said that engines running on unleaded gas will be rated for 3,000 hr TBO.

[201Steve]

@PT20J I’m not old enough to have seen it in the field, but didn’t autos with flat tappets suffer after the oils started reducing zinc levels in their products? 60’s maybe?