go team

So I have these camshafts that are worn that I thought would be a great way to trial liquid black oxide treatment on.

Some history:
These had the rear lobes worn (I can’t remember which bank) and I neglected to document the mileage when I came across these. It was stored at a shop with temp control and never cleaned from disassembly.


So after the treatment (I assume between 500-600 celsius) fine hairline cracks showed up which weren’t there before. I have chatted with another members on here and figured it was there from factory but one way to tell if the cracks were present before treatment was to use spot check to assess. I do have one more worn intake camshaft to try spot check on.

I decided to try black oxide because it helps with decreasing friction and also added strength to the shell. Also, it is common practice in the hot rod and muscle car world where flat tappets are more used. Further the temperatures used in this treatment are usually considered very low and cause “no distortion”.

I’m trying to review the treatment process to see if there was any deviations that could cause this. I was really hopeful that this could be a possible solution to the premature wear in these engines. If the camshafts show microns of cracks then a more invasive repair like a regrind and weld would be unavoidable.

Photos below:

hachiroku

wow...I wonder how AMG/Mercedes has produced camshafts for vehicles for so long but their process with the M156 is so bad.

skratch77

I believe the m156 is the very first engine built 100% by amg from the ground up. All other engines were modified mercedes engines.

DRBC43AMG

Outsourced production for parts and under par quality control IMO that should NEVER happen, not unless penny pinching accountants have their say...

hachiroku

things like camshafts though are a standard process. high performance engines nor economy engines should have different processes in camshaft manufacturing. yes, maybe they used a crap supplier, but generally these sort of things aren't outsourced to companies that don't know what they're doing.

maybe we could get a class action lawsuit going! i mean...supposedly even brand new cams aren't true and straight.

go team

So I’ve confirmed the treatment process. The cam was preheated to 420ish Celsius (800 F) then into 530 ish Celsius (1000 F). The cams tested 65 Rc (I think thats a win but I didnt check the before values).

I’m kicking myself for wasting a whole cam as I could have cut it in pieces instead of rendering the whole thing useless. I’ll be cutting my next cam into pieces so that we can try to redo the oxide coating again successfully. I’ve rechecked the lobes on my last worn cam and they seem crack-free.

Cwagon

Remember what Tasos found, where the oil holes on brand new camshafts weren't drilled through to the centre.

The Machinist

I think there are a bunch of problems with these camshafts, and it starts with when they were heat treated after being forged and rough machined.


Assuming that there is nothing wrong with the steel alloy, It is my suspicion that the blanks were left too big after they were case hardened. When the cams were finish ground, in some cases the grinder broke through the case, which is why we see such wildly varying degrees of wear, even on the same camshaft.

If the surface cracks were present, but not visible before nitriding, I believe it to be a result of the core metal of the camshafts to be too flexible, causing small surface cracks in the case that remained after finish grinding of the cams.

Now, if the cracks are in the nitride layer and not the parent metal, I think that the cams were allowed to cool too quickly after having been processed.

Another question to no one in particular is: what alloy are the cams made from, and what temperature to they start to lose their temper, and begin to anneal?

Heat treating of steel is a bit of a black art even to me. Metallurgy is one of the subjects in which I have a lot more to learn, however I do know enough about it to be dangerous.

My main ware in trade is precision grinding. So I have a lot of time at the control panel grinding heat treated metals and all of these things I have seen before.

An example of a similar phenomenon is that of “mud cracking” on chromed surfaces. If you look at the hydraulic rams on an earth mover, they are coated in chrome for surface finish and durability. Over time, the ram will repeatedly flex back and forth as it does work.

In bad cases the chrome plating will crack as a result of the less brittle parent metal being worked. The cracks that appear look like a dried up salt flat.

roadtalontsi

I can't help but think some of this is just complaining. It's a high revving large displacement v8. Nothing last forever guys. These aren't 120hp econo box hondas. The m156 has more than proven itself as a badass race engine. They are running them for 20,000 miles before a rebuild in the endurance racing GT3 cars. In fact it's so good they continued it on even after the SLS GT3 and into the AMG GT3 race cars. I know it sucks and it's expensive if/when it happens but it has always been a pay to play game in the race car world. At least we don't have crankshaft timing chain gears stripping out and engine main or rod bearings as a regular 80k preventative maintenance procedure like bmw. Cylinder head rebuilds at 100k in the porsche world are normal. Audi has stretched timing chains and oil consumption piston issues. Dodge... well they dont even make 80k. Viper engines apparently are lucky to get past 10k with their latest batch. ford? no clue the old ones used to spit spark plugs out of the cylinder heads, im sure the coyote has some weakness. You don't normally hear about issues like this in the LSX world because they've already taken their engine apart long before 80,000 miles to replace the heads, cam, stronger rods and high compression pistons etc... however they are notorious for oil pump failures which is catastrophic.
At least the camshaft / lifter stuff is relatively easy to do and doesn't require engine removal or complete tear down. Most of ya'll have leaking valve cover gaskets and front cylinder head covers by this time and need to change your spark plugs too. I'll take that any day over the above mentioned other brand issues.

deadlyvt

To be fair Ford remedied the spark plugs blowing out with an updated head that they wouldn’t come out of. Much improved !

go team

I didnt treat this cam with the intention of complaining lol

go team

The fun factor has disappeared.

deadlyvt

That’s crazy hot bad the metal is... pitting everywhere

go team

They’re not that bad I think that was just metal shavings stuck on to the wd40 I sprayed for cooling.

BLKROKT

So, let me preface this question(s) by saying that I don’t know anything about cams. How feasible would it be to get custom cams made out of a high-quality material? Seems that treating the OE cams isn’t really a long-term solution.

Do we even know the OE material composition? And what is the best material - billet, chill-cast, something else?

Surely one of the bigger companies could do it given a set of OE cams to work with, but I assume it would have to be quite a large order for it to be reasonably economical?

I see fairly low $ numbers thrown about for custom cams on domestic cars, why not for us?

go team

Kerry (the machinist) had found another option using old cores but ill wait for him to chime in on that.

Black oxide, if i ever get it to work, should prove to last quite some time as long as its maintained well with good oil and frequent oil changes. The heat treaters and myself were surprised to the cracking as their experience in the past had never resulted in wrinkled lobes only. Ive chatted with local hotrodders and they've also only gotten good results with oxides cams. It’ll be another 2 weeks before I end up with more findings, as long as I can slice this cam in pieces.

The Machinist

I honestly don’t have any idea what the factory cams are made from. Whatever it is, is definitely forged. It’s also been case hardened as Go Team found out when the cam said F**k You to his sawzall blade.

My suspicion that they ground through the case when they finish machined these is all but confirmed.

I bet if you test the hardness around the entire profile of the lobe, you’ll find that it is quite hard on the back side (valve closed) but on the ramp up towards the tip, the hardness probably falls through the bottom.

As for the expense of our camshafts, I think part of it is the “euro performance tax,” coupled with the small pool of potential customers for the maker of the cams. The most expensive part of making anything from scratch is the machine setup and programming, because during that time the machine isn’t making chips or grinder grit. When the machine isn’t doing those things, it is costing the owner money. Quality Swiss made CNC grinders that can grind camshafts (work spindle indexing) run north of a million USD.

That’s why it costs less per unit after a certain number of units are sold.

With regards to perceived complaints, hardly. Volkswagen has been using flat tappet lifters identical to ours in their high revving engines (basically every water cooled 4 cylinder on the road from the late 70’s until the early 1.8t engines came out in the early 2000’s. It isn’t unheard for one of those to last 300,000 miles. Audi had also been using flat tappet lifters In all of the 5cyl engines (including that fire breathing group B rally car in the 80’s) as well as all of the V8s up until 2001 when the 40v V8 came out.

Those things were all bulletproof as long as you kept up with timing belt change intervals.

I understand the pay to play thing, and I get it. It’s not a Chevy cavalier. I’m ok with $160 oil changes and $250 transmission services, $1000 brake jobs, and rear tires every 4 tanks of gas. Those are all wear items.

I do not consider a camshaft to be a wear item. Just like I do not consider the turbos on the old B5 S4’s to be a wear item, even though that is the inside joke.

There is a fine line between a wear item and **** poor engineering when the manufacturer acknowledges the fault but refuses to do anything about it. I recently found this out with the flywheel on my TDi.

Apparently VW considers the DMF on these cars to be wear items even when the clutch is in perfect condition.

I’ll end this here because it is getting long.

On to the next subject:

The Machinist

The company I found for the other option is a place in California called Web Camshafts or something.

Ive read everything I can about them and they apparently are well respected in the drag bike and motocross world.

At any rate, they have advertised in their catalogue of services a regrind (per set, 4 pcs) for 1100ish USD. Hard face welding of worn cams would be extra, but well worth it, I’d argue. The weld will be as hard as a coffin nail, and after the regrind you’d never know it was there.


They already have the specs presumably in program form, and I doubt having billet cams made would be out of the question.

hachiroku

yeah I did reach out to them in the past about billets...they won't offer it for the M156...probably due to lack of interest. their hard weld service requires you to provide grind spec to them, which could be a bit daunting.

The Machinist

I would have them grind the lobes undersized, weld and return to stock specifications.

VektorPerforman

Valvetrain metallurgy is very precise and often not tolerant of imperfection, as many of us know. My concern with an aftermarket replacement of any kind would be longevity. Most aftermarket cams are made for high performance conditions that come with short-use (inspection and/or replacement after X number of drag passes, or Y amount of road coarse hours) performance applications that have rigorous maintenance/refresh schedules. They also generally operate best with accompanying upgraded valvetrain components.

Regrinds make me cringe, but that's based of older experiences with different platforms. Similar things to be concerned with when choosing a regrind house; regrinding changes the metallurgy of the OE cams. Are they annealing after welding and re-heat treating? Further, are they using a heat treat and case hardening process that will produce OE results; hardness, depth of hardness, etc. With the processes necessary to get them back to OE specs, how are they straightened, and to what tolerance specifications (and what are OEM specs for concentricity, out-of-round, etc.). Then there's surface finish; probably one of the easiest things to mimic visually, until you look under magnification. Most welding processes come with microcracking, it is present here? Micro voids, inclusions, carbon chrome or various other deposits all can effect the friction/wear characteristics of the cam/lifter interface.

ShawnD72

Just following along, good conversation and info here Like to see where it ends up

The Machinist

These are all valid questions that I would pose to the regrind house before pulling the trigger.

The point of this discussion is that the OE metallurgy was inadequate. As go-team found out when he had his test pieces nitrided, the OE cams already seem to have micro cracks in the surface and no one knew about it until he had the nitriding done. The OE spec also seems to have a poorly planned case hardening job done.

He tried to section a worn camshaft for testing purposes and it made a fool out of his sawzall blades. HSS is no joke. It should cut through Cast iron-like metals like butter. The alloy that the buckets are made from is pretty much identical to the stuff they make bearing races from, and it is softer than HSS, yet they wear the cam lobes out.

This points to the factory case having been ground through during finish machining. This means that they left too much material on the cams before hardening them. A case hardened surface only extends about .020” deep, or about .040” on the diameter. If the cams are bigger than .020” “on a side” prior to the heat treat, the finish grind will blow right through it. Incidentally, this brings up another thought. If they case hardened them after finish grinding they might have been tweaked in the quench bath too. I need to mull that over some more....

I do have some experience with rework of precision shafting involving welding.

Usually, when you weld a shaft, unless you heat the shaft up beforehand the weld will tweak the hell out of it, and you’ll need to straighten it on a hydraulic press afterwards.

Im my previous life, I’ve seen some shafts have keyways blown right off from the torque. We’d weld them back up, and if the metal didn’t cool quite right the shaft would tweak over significantly. We’re talking about a 5.5” diameter shaft here. That went into a 200 ton vertical press to get straightened. We got it within .002” total indicated runout before the finish grind. After I ground the shaft (undersized) to get it perfectly straight we had it chrome plated, and I then ground it back to OE spec. You couldn’t even spot the line where the weld stopped with a magnaflux.

I doubt they are using stellite to weld these, but for example, when you weld with stellite you have to heat the parent metal up to a dull red, and keep it there while you weld it, and allow it to cool over a minimum of 24 hours. If you don’t do this, the stellite will crack and spall as the parent metal cools. **** sucks to machine.

I have been doing some reading up on valvetrain metallurgy. Camshaft steel is similar to cast iron in that it “self lubricates.” This just means it has a lot of carbon trapped in a porous structure. If I had to guess what they use to weld these, it’d be with nickel rod. I’ve seen some spectacular welding on cast iron like metals done with Ni rod.

The point is, if it’s done right there is no reason to expect a finished result that would be worse than a seemingly mediocre OE quality camshaft. I certainly wouldn’t pay what Mercedes gets for their camshafts knowing full well the problems that they all have. I am willing to pay $1200ish (for a set) to find out. It’s not like we are talking about $3500 for a set of regrinds from some of the other M156 supporting vendors that I have seen. That I would not do. New OEM can be had $700ish each.

VektorPerforman

All good points.

I'm personally not in this situation (yet), but it has me thinking. I'm tempted to keep an eye out for some good used cams/followers and explore the topic some. Based on my experience, I'd likely go the route of surface treatment, finishing, coating, or all of the above as a means of bridging the reliability gap. We've seen decent improvements applying some of these technologies to OEM (and aftermarket) cams/buckets/followers and it generally has a far lower financial impact.

roadkillrob

I wonder what all VRP is doing, I enquired with them last year and they have a proprietary grind that needs a tune but also said they could have a set ground to OE specs. They are using someone to regrind stock cams, not sure if they are welding them if worn or if just grinding undersized, but guessing they are welding especially as they are changing the profile if you don't ask for a factory grind, they also appear to be black oxide coating them.

I also talked to Jones Cams last year, they have the OE specs and will regrind but they don't build them up, they just regrind undersized they said, is cheap though like 150 each or something like that, but I don't think they realize or understand that they are wearing through the hardening and just regrinding worn OE cams without building them back up would just produce junk I would imagine, so guessing they have not done many or any in the past.