bhamg

In the second photo if one looks at the second bolt from the top, I think it's safe to say they're looking at the precursor of a broken bolt. Note the pitting in several areas. I'm also thinking that since the few confirmed reports (like yours) suggest some bolts indicate nothing out of the ordinary, as in state's car also, that certain bolts by location may be more prone to corrosion, no?

motoman

More arm chairing won't hurt while waiting on failed bolts...

The scenario I thought of looking at the heavily pitted bolt is:

Block sealant fails around headbolt threads.
Coolant is pushed up by ?20 lbs pressure entire length of bolt to flange
Flange keeps coolant out of top of head .Coolant begins to age.
MB says keep coolant 4 years.
Block not drained at year 4. New coolant not reach headbolt. More corrosion
Headbolt erodes under flange washer. Tensile strngth exceeded. Headbolt pops.
Old and new coolant is drawn into combustion chamber each intake stroke as gasket opens.

On the 08-09 failures there is marked corrosion just under the flange and balance of headbolt relatively clear of corrosion, possible the sacrificial coating is thicker there? AMG changes coatings on new bolts.

Any defect in forming the bolt head is magnified in this model. Does coolant need constant mixing in the engine ? If so water could separate and rise to top. HMMMM.

Critter

Motoman, you have seen the bolts close up, top bolt in pic of four seems to be almost perfect showing a touch of oil coating like on the head of the bolt. All seem to show some corrosion/discoloration from the head down the shaft at the similar distance? While there is little colour change on the threads, near perfect like new. Just what sealant does MB use when installing the bolts originally, I see no buildup what so ever.
In one test could you do a tensile strength to see if the protective coating will flake off near exceeded ranges.
My thoughts when looking at the bolts is that the material used is not up to consistent standards internally. Galvanic or electrolysis reaction on dissimilar material?
Although impossible, backtracking of the manufacturing process could differentiate what changes occurred from one batch of bolts to another, because obviously these bolts were not made at the same time.
Just how many engines are out there could be saved if the owner just ran 1/4 cup of oil in the cooling system to combat the bolt corrosion?
Keep up the good work gentlemen, would be very happy to be proved totally wrong in my thoughts and for you guys to be successful.

bhamg

Right now I have all the bolts, motoman has not seen them yet. statepkt sent me two corroded bolts, the broken bolt and one "good" bolt. motoman presumably will test three bolts (broken, corroded and good). I'm looking for one more broken bolt but will proceed with a separate avenue of analysis regardless of whether it's forthcoming, assuming I'm told testing only one corroded bolt will still yield good information and lead to meaningful conclusions. Perhaps I'll get the broken bolt back if it's returned to motoman in a condition that my testers can work with. We'll see how it shakes out.

brano_co

hey guys as I just find my engine is 569xx 60 057etc , I am expecting to have the "wrong" screws, so today asked at MB dealer how much will cost to replace them...

is here somebody who had this job done in central Europe ? How much that roughly cost (new OEM screws) ? in US I read here is about 2K USD, but think will be different in Europe.

I read in this thread it’s about 15 hour’s job, right?

also do have somebody over here maintenance manual for this job - what’s the order & torque for those screw ? - so maybe some not MB but well know garage can do this job ? or its better to keep this on local MB servis to do this ? (car is out of warranty)

What’s the % , so this can happen also on mine car - is there some other indications beside the water leak, but as I read here , this can happened just in few minutes without previous warning... ?
Have the car 3,5 month (with PP package – if this can indicate something ? ) bought it with 22,800 km (14,170 miles) on clock , now on 36,500 km (22,700 miles) topped the water just once – about a month and half ago (after blast in Alps roads at Grossglockner in summer) – so don’t know if the loosing of coolant can happen normally (maybe the water cower was leaking, maybe etc… you know just hoping the coolant wasn’t leaking cos the screws) , or if this is the first indication ?

thx for all advices


Brano

motoman

A lab's typical menu lists many tests for the customer to check and then there is the most interesting test, "failure analysis." Labs typically include several varieties of corrosion testing, including "crevice.". Interesting pursuit, and if successfull, should warrant a response from the "man."

Critter, interesting thought about the stretch/peel.

Brano, I have also asked about %, but I don't think we know. As stated before if the real total production of M156 is 100,000, what we can count on this forum is probably acceptable to MB AMG. So far my request for failed bolts in the other sub forums has yielded only one response, that to "visit C63 forum" where the headbolts pop often.

That does raise interesting questions too. Are C63 drivers harder on their machines (and so what?), and others more willing to quietly repair with big $$ as part of the MB experience. Don't know.

bhamg

Here's another interesting photo of the broken bolt. The full resolution photo obviously shows much more detail but posting here is what it is.

motoman

Contacting labs and reading their services is an education. Alas, the "failure analysis" has a final ring to it which is not necessarily borne out in the case studies offered at the labs. For instance very thorough tests which show e.g., the bolt is really a grade 8, heat treated and tempered properly . It snapped (my words). Too much load was imposed. Dear customer want us to investigate why too much load? And so on...

I am looking at the pictures of failed head bolts presented by forum members and really feel we need to also include (besides statpkt's) ones with the isolated white corrosion just under the heads a la merc63's taken out at Weistec.

Beside being several years apart in age, to me, the two examples appear to have a different coating on the heads, and shafts. Not positive , but the dark coating on merc63 may by phosphate or oil, neither of which is considered good by the experts.

The last bit is that the old style female bolt head configuation is primarily to support automated factory assembly. This style was abandoned with the "improved" style. Does this mean hand torque at factory due to problems, or merc63's theory of more material?

Still no failed headbolt offers from other forums here. I have forwarded the "50Nm and 3 turns of 90 degrees" as official M156 tighten spec, but labs are asking this 1st, so please, someone post the star page (thanks merc63).

Bud Wilkinson

Subscribed.

***EDIT***
Ok guys.
So I have been doing a lot of reading here of late. You can add my CLS63 to the list of causalities in the head bolt failure category. This is my third MB as I have become a loyal fan of the brand for the reliability and customer service of MBUSA. This head bolt breakage however is very disheartening, moreso as to how MB is handling the problem. This is without much question a huge design flaw in one of the main systems of this vehicle. I had done a Google search of "2007 CLS63 AMG common problems" and this didn't come up at all. Now had I done a search for "MB M156 Engine Common Problems" There would have been a lot to read, perhaps keeping me in the 2006 E350 for a while longer.
As it turns out I had the car for less than a week when the "Low Coolant" warning came on. No coolant on the ground. Temp Gage always around 90 Deg C. Refilled about a quart of water and drove for another week without trouble and then got a misfire with a P0308 DTC. Parked car for the night and got some white smoke on start up cold that went away rapidly. Missfire was gone and no other troubles seen till the next day. Missfire, Low Coolant and White Smoke at start up. Milky oil now seen on dipstick and on inside of oil filler cap. Local MB shop here said that I have a broken head bolt around #8 cyl causing all the trouble. Sucks that MB has no recall for a known failure of such magnitude and expense on the main system of the vehicle. After all a car isn't really a car without a functional engine.
Anyway after reading a lot here I will be contacting Weistec about their head stud kit and maybe more as long as it is apart. At the end of the day I love the car and want it back on the road. It is just to nice not to fix. Just wish this didn't happen and that MB would be more stand up about an obvious flaw in their parts.

Bud Wilkinson

After looking at the pictures of failures and the "New vs Old Design" picture here https://mbworld.org/forums/5563628-post30.html a basic stress engineering mistake went unseen. Perhaps if the bolt head were engineered a bit taller or taller and larger diameter there wouldn't be a problem but it was a clear effort to reduce weight. this is not uncommon practice.
Glad it wasn't a dam or bridge but still unhappy it was my car.
At the end of the day, Mercedes Benz still has to compete with the likes of Acura, Infinity, Lexus, to whom the new CLA is clearly aimed at, among others that were previously unsuspected.
To turn your back on your customer base that is, let's face it an AMG customer is, above average is a marketing mistake when the other manufactures will goodwill cover many things to retain customer loyalty.
Bad move Mercedes and AMG.
I Call

Sincity

Bud: Have you taken it to the dealer yet and see what Mercedes will do as far as covering some of the cost?

Merc63

Tightening of the cylinder head bolts must take place according to the numerical sequence given in the figure. Loosening of bolts takes place in reverse order.

1 Tighten cylinder head bolts (1 to 10) to stage 1.
2 Tighten cylinder head bolts (1 to 10) to stage 2.
3 Tighten cylinder head bolts (1 to 10) to stage 3 (follow-up tightening).
4 Tighten cylinder head bolts (1 to 10) to stage 4.
5 Tighten cylinder head bolts (1 to 10) to stage 5.

Merc63

This is what I used when I did my studs to remove the stock bolts and install the studs. Except for the studs, I pulled one bolt and replaced with a stud, torqued to 100ftlbs.

After all the studs were(100ftlbs) in I torqued them to the ARP/Weistec spec in the above MB pattern.



I think motoman was looking for this info for the stock bolt torque procedure, there it is.

Bud Wilkinson

Hey Sincity,
I have the car at a very good Independent here locally right now who knew of the problem and of some MB document prescribing the repair procedure and necessary minimum parts replacement encompassing the SLS valve buckets, crank and rod bearings as well as replacing the affected piston, #8 in my case.
This is my 3rd Mercedes but I am an Acura, Honda and ASE master tech so have done all the maintenance needed myself and have only bought a few parts from the local dealer. Not a great relationship there.
Regardless, I did call today and spoke with the Service Manager who had "Never heard of that in 22 years at Mercedes" "Too bad that at 74000 miles and the 3rd owner that there is no warranty available for you. Have a nice day". Still not a great relationship there.
This same dealership sales department allowed my wife and I to just walk away with checkbook in hand, money in the bank, ready to make a deal on a CLK Cab and an ML at the same time after test driving both vehicles. This indicates a pretty low motivation level on the part of all parties involved there.
My career path has taken a different turn now so I have no real place to do the work. I feel as if I am in great hands with the shop the car is at now. Having been a shop foreman at the Acura dealership level, I can usually spot those who are incompetent, competent and above average. The local shop falls into the later category. I may still clear out my garage and do it myself. I don't know if I can afford the time.

I really appreciate the support and information here on this forum so please keep it up.

Bud

Bud Wilkinson

Merc63,
Thanks for your tireless efforts here to give information and share so freely with us all. I will be taking your advice on my build to use those super beefy Weistec studs. I am not in need of the stage 3 kit as you have done but then again, who really needs it. Just a blast to have I am sure. The stock 507 works great for me.

Bud

Ingenieur

on the old bolt
are there any markings?
what is the shank diamter?
what size torx?

can someone measure with a mic'
the distance from the top of the head to the bottom of the flange
the depth of the socket recess
???

whatever torque that is applied is stored as stress in the bolt and transfered to the threads and the bottom of the flange
and the flange load point is obviously the weak spot

solekeeper

Guys I'm looking at pre-owned 63's, how would i know if the motor has been affected?

motoman

Merc, Thanks, I also dug out the tightening sequence on a FelPro site.

Some random stuff...I hope that this is taken as information and not a sermon.

The best pictures I have found of a failed head bolt shaft is on "marcusfitzhugh.com." It matches the classic failure known as "cup-cone" ductile fracture on the lab sites. Problem is that "so what?" The final failure is not definitive. For instance , IMO , corrosion and over torque at factory cannot be ruled out. If the otherwise good fastener is asked to do too much it will fail. (Look at above picture and see what looks like brown corrosion at the edges of the fracture.)

It is possible MB dual sourced the headbolts, and did not control by serial number. If this happened MB could only bracket the production run (2008 to 2010), but not isolate the cars. It should be possible to identify the headbolt manufacturer by logo impressed on the head. A mfgr logo index is available. If 2 or more sources are identified, one bad, then a random
mix within engines is possible, some ok, others mixed. A bad bolt among the others could break and overload good ones (ductile failure above).

SIDE NOTE: Off topic. Looked at a lot of class action info and have some comments, but you will have to convince me to post it and where.

motoman

Merc, Did I read that the studs require a retorque after the head and gasket settle down? If so that requires a second effort versus the improved TTY headbolts?

Critter

Motoman, picture of the head bolt on that site Marcus blah blah.com shows a stamping of R I T on the top of the bolt, which should be the manufacturer of that bolt, any correlation to that RIT and to the failed bolts stampings, same or different? Which would throw some light on the multiple source suppliers theory.

hasse_231

Hello this may be a stupid answer, but i have to be sure.

As i have read is that Mercedes did upgrade the crank, pistons and flywheel( 3 kg Lighter) for the newer C63 amg with pp from 2010 and also increased the hp to 487.

Are these Cars affected also ?


When did C63 get the updated Gearbox with s+ mode ?

When did the c63 get the updated MCT Gearbox ?

Thanskful for answers !

motoman

Critter, thanks for the involvement. I will look on the index I have . The significance will have to wait to see if two or more logos appear. I'm glad you could read the logo as it looked like it started "H" to my tired eyes.

Critter

Another observation is that the site bolt from marcaus site is a black colour whereas we have seen the gray/silver colour on the failures? Is one coated with a rust preventative- gray finish and the black is a different supplier, with case hardening.
Any other markings on the bolts received?

Ingenieur

if we know
the bolt spec
the torque
the approximate combustion pressure
we can calculate the stress in the material: (preload tension + combustion pressure force)/area

we also know where the load is applied (it's trying to pull the bolt down the hole, ie, on the flange, and in the oppiste/equal direction trying to 'strip' the threads)

there are programs that will model this to a very (and undebatable) degree of accuracy

we can estimate the area that the force/stress is distributed over and determine whether it's > than the tensile strength of the material or the rating of the fastener system

now factor in a cyclic load, ie, the combustion process, load/unload and this will fatuigue the bolt faster, and some bolts get more of the distributed load than others (probably the ends...do any specific bolts fail? is it usually an end one?)

engineering calculations are difficult to dismiss and the obvious question is if the original bolts were properly engineered why did you change from an internal torx to an external torx?

there may not be enough incentive for a class action but I honestly believe one could be successful in a suit...it takes perserverance (took me 2 years to get satisfaction from BMW NA, but I got it, plus my legal fees: I prepared the arguement and had the attorney do all the filings/paperwork, it went to arbtration and we prevailed)

I just hope I don't have to be the first to prosecute one

motoman

Critter, I looked at my 2 indexes and did not find RIT. There is a euro handbook to logos available, but I'm not interested @$60. The two sources I found are "eurofasteners.com," and "efcog.org" which offers MIL-HDBK-57F. Some German ones in latter.

Yep, the coatings are also suspect. The pickling @ 800F prior to hot dip galvo can ruin the previous tempering and introduct hard spots which can crack. There is too much to guess. A lab looks at all this, for a price.