Were there any ID markings on the bolts that have been received so far, like has been said before chances of a single source supplier for bolts for all years is highly unlikely.
Just what pickling is done at 800F are you speaking of, a cleaning prior to corrosion resistant coating. Do not think it is galv as it provides little strength and would be difficult to have equal coating depth which would not agree to stretching of the base material. There seemed to be some Russian symbols on the bottom of one picture I seen, will send them to a German engineer for his input.

 

Copy this to Microsoft Word and increase the size of the picture for a clear view, Looks like RIRE on top unsure of the symbols on bottom.

 

Critter, great pics. The world of coatings and processes is very deep. I only pick out some stuff that seems relevant. I don't know what anti corrosion has been used, but the "pickling" example was from a lab which found areas of very hard steel where all should be uniform , ductile. (They found matensite which had been produced by failure to withdraw the fastener from the tank in time. The fastener core had been transformed)

This may bore some readers. I can send you all the sites I looked at if you want?

Another obvious thought. If MB stayed with the same vendor who produced a bad lot along the way...all the more difficult to control effects by car SN.

 

Would like to put my money on the idea that there were multiple suppliers throughout the years the engine was built. Quality control within Mercedes must have diminished as we all know a bolt is a bolt, right. Many inspectors are notorious for getting too much sleep on the job.
What really blows my mind is that I have a 40 year old car with a 20 year old rebuild on the engine using the original head bolts and you know what not one has cracked or broke and it's a Dodge small block that used to turn 7k in my youth ha ha now its just a fair day car. No coolant lose, no oil smoke and no CEL. LOL

 

Critter, Yeah my lowly 2,8 all iron has never been apart 1985, 140K. But it is hardly a comparison to the 6.3.

LOL at the "Russian" symbol...But this global thing is strange. I have some excellent Russian drills. An I don't forget my 87 Audi which had a Japanese made radiator, 150K.

Quick aside I ran accross: In the 1990's the Feds were up in arms over counterfeit fasteners and tried to impose registration . Later US Patent office got involved.

I could not bring this German handbook up to look at it :EN 10269:1999/A1:2006/AC:2008 FASTENERS HANDBOOK H-131.

 

the markings are read as follows:
there is a reference dimple/dot, this is 12 o'clock
then there are dashes, 1 = 4, 2 = 6, 3 =8
if you have 1 dashes at 4 oclcock grade = 4.6
if you have 2 at 10 oclock = 10.8

the picture is not clear enough to tell and at an obtuse angle
the letters are corrosion and material info
are the 4 large letters are the mfgs code 01?F ???
I think the stylized W is the mfgs mark

I think it is an 8.8

this lists US registered mfgs by code and symbol (our bolt may not be US registered) http://www.google.com/url?sa=t&rct=j...qHemaPS3-C3LBA

 

Merc, thanks, I found this restricted to 2007-2008. The engine numbers are 156.980, 156.982, 156.983, 156.984: It is not official MB but references them.

1st torque bolts 1-10 to 7.5 ft lbs
2nd torque bolts 1-10 to 37 ft lbs
3rd turn bolts 1-10, 90 degrees
4th turn bolts 1-10, 90 degrees
5th turn bolts 1-10, 90 degrees
6th torque bolts 11-14 to 15 ft lbs.

 

solekeeper, look at all the headbolt thread. I think someone estimated out through mid 2010, but there is still some discussion

 

Ingenieur, you may have hit it ...found:

"l W l" is Herman Winker
Spaichingen , Germany , and has auto fastener patent. Let's keep looking for more.

 

I'm going to remove a valve cover to get a good look at a bolt (as long as it's not too much of pita)

 

IIRCIIRC the latest head bolt failure to date that we know of was in a July 2010 production car. If not July the it was June.

 

And I'll report back on the four bolts (statepkt's) that I have when I get home in.a week.

 

imho and WAG is that an inverse torx should have not been used
the static rating is sufficient, but when flexed/fatigued it may eventually fail

if a joint is fixed probably fine (in the case where clamping force resists movement) and the loading is in shear (other than the tension required to generate the clamping force)

not the case here, the bolt is in tension trying to prevent the head from being blown off, lol, so preloaded in tension, and the force acting increases tension

the force is trying to pull the screw into the hole, and the torx recess can deform/flex
an external torx doesn't have the void and will resist this much better

the 64k$ is: why if the inverse were fine why the change to an external torx?

how bad of an isssue?
no one knows
depends on the load over time the engine sees I'm guessing

I don't think it was a production assembly issue (ie, torqued incorrectly)

of the documentated failures is it the same bolt? a corner bolt? or random?

 

I saw this mentioned earlier in the thread and wanted to add some data points from my own used car search:

Build date 05/31/2010 serial: 526091 engine: 059999 (MY 2011)

Build date 06/04/2010 serial: 528072 engine: 060475 (MY 2011, maybe the same car mentioned earlier)

Build date 06/25/2010 serial: 539180 engine: 060975

Build date 07/05/2010 serial: 543018 engine: 055331 (weird huh)

Build date 07/07/2010 serial: 544014 engine: 061702

Build date 08/31/2010 serial: 547551 engine: 061152

The cutoff date appears to be in June 2010 (ie early Model year 2011) and serial number around 530000, but given the out of order engines, who really knows.

Agreed that it affects ALL MY2010 C63s. I was hoping to pickup a late 2010 with newer headbolts, but they don't exist.

 

Is there any logo apparent under the galvanized head of the "improved" bolt? A little buffing perhaps? If a wholesale switch to the male style was made , perhaps this was the vendor's offering. With an AMG drawing change.

In reviewing many headbolts used in other MB engines Viktor Reinz is dominant with both tall headed (diesel) , but also the female style.

It would seem AMG blue printed the bolt and put it out for bid?

I believe some people have mentioned the cyls where the bolts failed, but that data it is mostly lost at indys.

 

Ingenieur,
I think you have stated it Well and truly indeed.
While there are other engines with the inverse torx as a head bolt and a TTY bolt as well. The others are not producing the same forces that these MB bolts are seeing for one thing and they seem to be of a different mfg process and or material too boot. The examples I am speaking of are from a 1996 Ford 4.0L OHV push rod engine with substantially less compression ratio. and the last stages of angular torque seem to be less overall.
Here is a close up of the bolt head from the rear of the left bank at the outside corner or #8 cyl of my stricken 07 CLS63. I also don't see any radius around the head from the stem either but don't have a whole example to look at right now. This one manufacturing step increases the bolts tinsel strength by 18-20% at the location as well as removing any 90 degree stress risers that may exist without it. Case in point would be the 12 point NAS bolts used to hold together commercial jet engines. This is a mil spec that has been universally adopted over the decades as a manufacturing standard for critical component assembly.
It will be all better in a couple weeks.

 

The bad news is that I can't really tell what the markings are on statepkt's bolts. I could if I cleaned the bolt heads up a little but I'm not going to do that prior to any testing...

 

These pictures are interesting for absence of corrosion. Any coolant tips here?

The "stylized" W is not visible to me. If there are several vendors a pattern of failure in one only could give some hope .

Merc63 and Weistec bolts showed what looked like tilting of the unbroken bolt heads. Happened in removal or?

 

Valid point about lack of radius! I believe we are looking at different manufacturer's.
Yes just what was used in the cooling system, change out, additives? or untouched?

 

motoman,
I know you have read volumes about the subject of micro corrosion I think it is termed. That may or may not be in play in many or even this case. With all due respect I feel that for micro corrosion to be a factor there has to be an entrance for moisture and oxygen so corrosion can take hold. Something like micro fractures at the stem / head joint have to be present for this to get under the coating and deep enough to be the root cause making it not the root cause at all.

Coolant Tips = Keep it full and in good condition.
Vendors = I Don't Know.
Tilted Heads = I have only seen this broken off head. I will inspect the rest after the job is done and post pics.

My take on it as a design engineer is that this is simply a poor choice of fastener for the duty. Here is a 20/20 hindsight list of things that may have prevented this from being a problem on what would seem to be an otherwise stellar, award winning engine design.

1. Radius at the head / stem interface.
2. Larger stem standard torx bolt increasing the material from tool cut to stem edge.
3. Engineering a non standard inverse torx bolt with a taller head and the same inverse tool cutout depth.
4. Use anything but an inverse tool cut fastener.
5. More fasteners designed into this interface / joint.
6. Proper metallurgy of the material to not be so brittle.

Bottom line is that bolts fail however never should a bolt fail in this manor. Without an exhaustive engineering study of the failure from forces to materials we will never know what the root cause is or if any of my suggestions on the list would have been the answer.

I know they have become the standard but I am also not a fan of the TTY bolt. I believe this invites the opportunity for micro fractures whether they are effected by micro corrosion or not, any fractures are bad. How many decades did we have a quality bolt, gaskets and appropriate torque values holding engines together without that being the root cause for any failure?

 

I guess I am unlucky enough to have joined the club. My 2009 C63 is currently in the shop. 51k miles. Started a month ago when I noticed the coolant light. Brought the car in and they replaced the cap or something. Light came on a few weeks later and just got the call that the head bolts are the issue. Worst part is that I brought the car in originally exactly one day after the warranty expired.

They said costs would be about 8k with 3,500 in parts alone. I have read through all the posts but some were unclear as to what the dealers did for you on this. The rep said he is going to corporate and is "in my corner" but I want to know what I should expect/demand. So what is it? Split the costs? Fully covered? Up the creek?

Also, is my case strengthened by the fact that they misdiagnosed the problem originally?

Thanks alot in advance. First time posting and really wish it was under better circumstances. Maybe they will give me a deal on a 2014.

 

Bud, Good discussion. Perhaps cyl 8 is a "dry deck" (ARP lingo for no threads in the coolant area), hence nice and dry.

The bolts bhamg has are heavily pitted. We do have reports of fissures under the heads of broken bolts.

I reread the ASTM wedge test. They call it a tensile test and will not allow a bolt to fail there, only at the threads. Could any of these have been from a passing lot?

Lots of discussion on line about the die strikes in making cold headed bolts and weakened area/ stress risers under the head... on and on.

The guys in the labs with the scanning microscopes can unlock this mystery. I don't think we can.

Might help to see if there is some pattern in cyl location , vendor / lot ID.

It would seem the collective knowledge here could generate some rework/repair instruction for those brave enough. At least do's and don'ts?

 

A long shot at bolt head logo... found: " RIBE " , Richard Bergner GMBH , Schwabach Germany. This mfgr does not appear as auto specialist, produces various fasteners. Has cage code . Could not find more.

 

Sorry to hear about your troubles. Hope MB will cover you.

 

I am going to look at the disassembled engine today if I can and take some pictures. I'll see if the bolt in question is "Dry Deck" or not and if there are others that have more or less corrosion and tilted heads. My first thought is the tilting of the heads happened on removal. Could be wrong though.