Is this cam hosed?

[N201MKTurbo]

DLC may help, but what you are seeing on the cam is spalling. Everybody thinks it is corrosion, but if you research it you will come to the conclusion that all research shows is sub surface stress cracking. It is caused by plastic deformation of the metal by poor lubrication, or impact stress. The stress cracks form along grain boundaries and individual grains are ejected.
 

In this case, I think it was caused by the improper valve spring. It is quite possible that now that the correct spring is in place, the lobe will just wear smooth. 

[MikeOH]

32 minutes ago, N201MKTurbo said:

It is quite possible that now that the correct spring is in place, the lobe will just wear smooth. 

I thought camshafts were SURFACE hardened.  Once that surface has been compromised/penetrated the metal will continue to wear even if the cause of the spalling is removed.  Do I have that wrong?

[carusoam]

That brings up the next question…

How deep is the surface hardening of a cam lobe..?

How much grinding can we get away with…?

This is all probably measured in thousandths…

So visiting a good cam shaft shop may be a good idea if going this route…

PP thoughts only, not a mechanic…

Best regards,

-a-

[N201MKTurbo]

Just now, MikeOH said:

I thought camshafts were SURFACE hardened.  Once that surface has been compromised/penetrated the metal will continue to wear even if the cause of the spalling is removed.  Do I have that wrong?

No, you don’t. I’m no metal expert, but I’ve read quite a lot about it. 
 

The case hardening goes deeper than I thought. The hardened metal is actually more susceptible to spalling than softer metal.  I was talking to the cam overhaulers about 6 months ago. They said they will regrind a cam and then do a Rockwell hardness test to the lobes. If it fails they reject the cam. They said they can usually go 0.030 before they hit soft metal. The pits on the OPs cam are probably less than 0.010 deep. 
 

The softer metal will deform under stress, where hard metal will crack. The flip side is soft metal wears very quickly where hard metal wears very slow, so choose your poison. 

[A64Pilot]

I believe cams, lifters and crankshafts are nitrided either by gas or plasma, which lays down a coating, which is different than hardening.

Hardening is a form of heat treat, it may be that induction hardening is common now?

‘I thought they were re-nitrided when re-ground but am not sure, a quick call would verify.

 

[EricJ]

Just now, Freemasm said:

It is not a coating. Nitriding ops introduce N2 into the parent metal. The PM properties determine the max depth but it's commonly only in the ten thousandths to a few thou. Probably technically case hardening.  The cylinder ops I've seen are done at elevated temps with gaseous ammonia as the N2 donor.  

Nitriding is case hardening.   

 

[Hank]

2 hours ago, EricJ said:

Nitriding is case hardening.   
 

And is a couple of thousandths of an inch deep [every time I've had it done].

[N201MKTurbo]

https://en.wikipedia.org/wiki/Case-hardening#:~:text=Time and temperature determines how,is up to 1.5 mm.

The article says that case hardening can go as deep as 1.5mm (0.060) and is typically about 0.030" Which is what the owner of the local engine shop told me.

[Hank]

4 minutes ago, N201MKTurbo said:

https://en.wikipedia.org/wiki/Case-hardening#:~:text=Time and temperature determines how,is up to 1.5 mm.

The article says that case hardening can go as deep as 1.5mm (0.060) and is typically about 0.030" Which is what the owner of the local engine shop told me.

Case hardening is usually a heat process [in one or more furnaces, with controlled cooling periods], and is typically as you describe. Through hardening takes much longer, and results in similar hardness all the way through. To heat the center of a 1" bar to the same 1700ºF as the outside [a typical steel hardening temperature, varying by steel type and often higher] takes much longer than just getting the outer 1/16" to that temperature. Long time in the furnace = lots of fuel / high electric bill, fewer parts hardened per day ==> higher cost. Thus we often only case harden, which is often sufficient.

[dzeleski]

Cams hard surface hardened and can also be coated. In either case that camshaft should not be in an engine let alone one that flies. The lifter that lobe was riding on is probably also toast, or will be toast. This is also an F which means its a 4cyl, 3cyl with a 4th dragging will not make enough power to get you out of trouble and if it gets bad enough youll be lucky to hold alt.

If one of my race engines had a cam in that state it would become a wall ornament and they operate on the ground.

I get its expensive but Im not risking myself, friends, family, etc with something like this.

[N201MKTurbo]

These guys say they do aircraft camshafts. They harden to 0.125"

https://blog.metlabheattreat.com/posts/heat-treating-camshafts/

It looks like all case hardening can warp the parts. I would think the hardening should be done before the initial grinding. 

[EricJ]

5 minutes ago, N201MKTurbo said:

It looks like all case hardening can warp the parts. I would think the hardening should be done before the initial grinding. 

On automotive engines it seems like any grinding at all on a nitrided surface removes the hardening.   People kill cranks all the time by either trying to salvage a crank with a spun bearing or regrinding a rod journal to increase stroke.   It seems like it always ends in tears.

 

[A64Pilot]

18 minutes ago, N201MKTurbo said:

These guys say they do aircraft camshafts. They harden to 0.125"

https://blog.metlabheattreat.com/posts/heat-treating-camshafts/

It looks like all case hardening can warp the parts. I would think the hardening should be done before the initial grinding. 

I believe your correct, cams, cranks etc are hardened first, then ground or turned, and that hardening goes pretty deep of course or you couldn’t  grind a cam 

‘I don’t want to start an an argument, but I believe case hardening is different than nitriding, case hardening is to make a surface very hard, but if the whole part was heat treated to the same level, it would be brittle, it’s heat treating often done now by induction and I believe is one lobe at a time, not the whole cam. and it’s pretty deep, but it’s surface heated not the entire part

Nitriding may not be a coating, I probably misused a term, but it’s a relatively thin layer that is chemically changed, treated whatever. Similar in effect to alodine, in that alodine isn’t really a coating, it’s a thin layer of the aluminum that’s been changed chemically, just many of us think of it as a coating 

So a new cam blank is first case hardened, then ground and finally nitrided.

‘I assume and am not sure that maybe a reground cam is reground, checked for Rockwell hardness to ensure they didn’t go through the case hardening and if it passes is sent of to be nitrided.

 

Edited June 16, 2021 by A64Pilot

[EricJ]

10 minutes ago, A64Pilot said:

‘I don’t want to start an an argument, but I believe case hardening is different than nitriding, case hardening is to make a surface very hard, but if the whole part was heat treated to the same level, it would be brittle, it’s heat treating often done now by induction and I believe is one lobe at a time, not the whole cam. and it’s pretty deep, but it’s surface heated not the entire part

Nitriding is case hardening.   A simple web search will confirm this.  Rich already cited a relevant link.

 

[EricJ]

Just now, Freemasm said:

Don't confuse case hardening (or any heat treatment) for strength versus for wear. We are typically talking about the latter, here. Two completely different applications. Any of the aforementioned components that would get through hardened would probably shatter in very short order. Calling any relevant materials engineers/metallurgist to speak up and get us straight.

Yes, case hardening typically makes the surface of the item more brittle.   This is why you really, really don't want to drop a crank or cam or anything with much mass that's been hardened as it can start a crack.    It's also one of the reasons why sudden stoppage is an issue, as it can crack the hardened surfaces on the crank.   

[N201MKTurbo]

http://www.aircraftspecialties.aero/camshafts/

these guy grind a lot of cams.

[A64Pilot]

2 hours ago, N201MKTurbo said:

http://www.aircraftspecialties.aero/camshafts/

these guy grind a lot of cams.

Interesting, they Parkerize which I’m familiar with from weapons.

[Guest]

I’m not sure I’d put a reground camshaft in an engine, a new 4 cylinder one less than $1000.  I’ve seen a number of them go bad in a few hundred hours.  The cost of replacing it again far exceed the difference between a reground and a new one.

The one in my 720 is $10K, that might get reground.

Clarence

[Shadrach]

1 hour ago, M20Doc said:

I’m not sure I’d put a reground camshaft in an engine, a new 4 cylinder one less than $1000.  I’ve seen a number of them go bad in a few hundred hours.  The cost of replacing it again far exceed the difference between a reground and a new one.

The one in my 720 is $10K, that might get reground.

Clarence

We reused our camshaft at overhaul but it had nothing to do with cost. Ours had lasted for 34 years and 1855hrs without spalling. There were years when that engine didn’t run 5 hours. We figured that a Lycoming cam that lasted that long it was less risky than a new one.  When I sent the crankcase out for overhaul 10 years later the cam still looked great. I may be inclined to keep it during the next overhaul if it still meets spec. A Lycoming cam that’s held up for 55 years and >4000hrs might have lived that long for a reason.

[Hank]

5 hours ago, EricJ said:

Nitriding is case hardening.   A simple web search will confirm this.  Rich already cited a relevant link.

 

<Note to the gentle readers:  epic rant follows. Don't espouse your "knowledge" based on a quick Google search. Some of your readers have real knowedge . . . . >

Nitriding is case hardening by applying a hard outer layer of, for example, titanium nitride or aluminum nitride to the part in question. It's harder than a file (filing a nitrided part will clean it and make it shiny, but it also dulls the file very quickly). It may be 0.001" thick, sometimes even twice that if you ask for it to be done.

Case hardening in a furnace is different, nothing is added to the steel. The part in question is heated up to change the phase of the steel and arrange the various atoms into a different structure. Controlled cooling is also required, lest the pesky atoms rearrange themselves back into the not-so-hard structure they had before. This won't work with low-carbon steel, there needs to be at least 0.5% carbon in it; traces of other elements will affect the temperatures required and the resulting hardness. Works great with many tool steels.

At work, I harden various tool steels for wear resistance. Typical values are HRc=50-52, although some steels can reach 56-58 without becoming brittle (things like CPM9V get quite hard, much more so than H13, with greater wear resistance. But much more expensive to buy, more difficult to machine and require hotter temperature to harden). What kind of wear? It sits 1/8" away from a 1/4" hole through which molten fiberglass-reinforced nylon is injected at 600°F and 30,000 psi. After a half million cycles, there is wear that we can measure (almost 0.001" deep) and they are replaced.

When making hardened parts, the piece is machined to size and often left 0.001-0.002" oversize, then heat treated, then cleaned up by grinding, high-speed milling or lathe turning with diamond tools. More reasons why hardened parts cost more.

The only difference between case hardened and through-hardened parts is the time, trouble and expense to make a large part hard all the way through--depending on size, it can sit in the furnace for a long time near 2000°F, and cooling the center can be difficult. 

I have seen nitrided parts, almost 0.001" deep, run for decades without issue. This is common in industry for sliding parts. Quarter inch diameter pins that slide forwards and backwards two or three times a minute, twenty four hours a day, several million times, often several dozen at a time being pushed with 8-10 tons of pressure. Large pins, 2" in diameter, used to align two halves of a mold as it closes, twice a minute, with 40-50 tons pushing them when they engage. In over 30 years, I've seen guide pins break twice. Hundreds of molds, millions of cycles each, at five factories (one had 400 active molds, several dozen built in the late 80s, untold millions of cycles, still in production two years ago with the original nitrided guide pins and ejectors).

Hardening is a complex subject, best done by someone experienced enough find and follow the steel mill's procedure. Sure, you can grind a piece of O-1 to an edge, hit it with your propane torch and dip it in some water, and it will be a functional cutter. But that ain't what we're talking here, and it ain't how cranks and cams are done . . . .

[A64Pilot]

I had my cam and lifers reground on my 540 when I overhauled it, I trust the old cams.

‘Somethings different with these newer cams, I have no idea what, just the old cams,I’m talking 60’s and 70’s, and 80’s just didn’t have these issues, my guess is some process spec has changed, but that’s a guess.

Lycoming gets their cams from Crane Cam? At least I think so, but that’s second hand so not sure. I don’t think Lycoming manufacturers their own cams

Edited June 17, 2021 by A64Pilot

[Guest]

2 hours ago, Shadrach said:

We reused our camshaft at overhaul but it had nothing to do with cost. Ours had lasted for 34 years and 1855hrs without spalling. There were years when that engine didn’t run 5 hours. We figured that a Lycoming cam that lasted that long it was less risky than a new one.  When I sent the crankcase out for overhaul 10 years later the cam still looked great. I may be inclined to keep it during the next overhaul if it still meets spec. A Lycoming cam that’s held up for 55 years and >4000hrs might have lived that long for a reason.

Was your camshaft reground?  The regrinding it the part I worry about, loosing how Lycoming manufactured them in the day.

There was a time when virtually every part in our engines were made in Williamsport, the days before out sourcing by the bean counters.

Clarence
 

[Grandmas Flying Couch]

Just now, M20Doc said:

Was your camshaft reground?  The regrinding it the part I worry about, loosing how Lycoming manufactured them in the day.

There was a time when virtually every part in our engines were made in Williamsport, the days before out sourcing by the bean counters.

Clarence
 

What do you think of the superior brand cam?  I wonder if they are better made?  

[Shadrach]

6 hours ago, M20Doc said:

Was your camshaft reground?  The regrinding it the part I worry about, loosing how Lycoming manufactured them in the day.

There was a time when virtually every part in our engines were made in Williamsport, the days before out sourcing by the bean counters.

Clarence
 

I don’t know. I’ll check the log entry over the weekend. I was pretty wet behind the ears when the engine was OH’d.   The original engine from 67 was removed in fall of 99 and returned to service in 2000. You can imagine the expectation given 3X calendar TBO and 1900SNEW with several inactive years.  I recall that the assumption was that the cam would be trash.  The engine had developed a slight “tap”.  The overhauler was very surprised to find the cam in excellent condition. The tap was collapsed lifter. I am sure the cam was sent out for certification. To what degree it was reground/resurfaced, I’ve no idea. The engine was opened again in 2010 (1X calendar TBO and ~850SMOH) due to a case crack. I was less wet behind the ears and nervous about the cam. Engine builder once again was surprised at the excellent condition of all internals. It’s anecdotal, but my experience suggests something has changed with the manufacturing. I’ve read too many reports of cam failure in engines that are both younger and more frequently flown than mine.  

[Grandmas Flying Couch]

Thank you guys for all your help!  I have a few choices:

1. Ship it to Lycon 12k Iran w new cam and lifters or 20k overhaul they said they had a six month wait!

2. Order the parts and do it myself.  I would like to do it myself, I'm mechanically confident and meticulous. 

Does anyone know an AP that would be comfortable with this idea in the Phoenix area?  Inspecting along the way and signing it off?  

This would be new cam, DLC Lifters, new bearings, moh gasket kit, ring kit, hone cylinders, wrist pin bushings, would only change rod bearings if mains were contaminated, if so would have to order rod bolts.