ZephyrAMG

When are you guys doing coolant flush and change? I know that it is recommended at 100K miles. Is it better to do it more often? Will it prevent any corrosion to head bolts and keep them in check?

whoover

The old style head bolts break because they have a weak spot, not because of rust.

Ingenieur

no
wrong hardware for the application, internal vs. external torx

motoman

Mulitifaceted problem. We are all presenting theories, but there are some factual clues. The photos show "white rust" where the zinc coating at the head area has sacrificed itself leaving the bare steel. Another "famous" photo on two other web sites (not those below) shows dramatic ductile failure, but around it is a loss of up to 50% of the headbolt section due to corrosion. The better headbolt buys time, IMO. And the extreme corrosion (pitting) has yet unknown total ingredients. Chemists tell us more about worrisom pH level, please. It is not as simple as 7.0 and above is safe, according to others who identifiy themselves as authorities?

Ingenieur

The fact is MB changed the bolt type
The coolant spec and change interval remained the same

ZephyrAMG

My intuition tells me that changing out the coolant will refresh its anticorrosion properties. Old coolant or broken down coolant will promote moisture and chemical rusting...

Ingenieur

other engine types with the proper bolt type and the same coolant regime are not failing
if it was the coolant it would afect all engines across all manufacturers

they used the wrong bolt
they discovered it and changed it
if they thought that changing the coolant more frequently would help wouldn't that be cheap preventative maintenance and wouldn't they recommend it vs. a rebuild after failure?

the head is collapsing (or being drawn down into the hold and into itself) during the power stroke (the head is being pushed outwards)
this is fatiguing the bolt over time and it fails at the shank/head area
the new bolt has much more meat and can't collapse since it is solid (vs the old one whose head is hollow)

motoman

What about "prying" forces acting side-to-side on a bolt head where the filet has been corroded away and where the diameter of the bolt has been reduced? This action is tested in the qual reliability testing.

Ingenieur

with the clamping force involved the head is not moving x or y, only barely z
not really moving but restraining force resulting in stress
what force would cause it to slide up/down or fore/aft?

JRSJR65

Question (without doing any research on forums forgive me), I have a shop with necessary tooling & equipment I am pretty sure to do this job. I've built several engines, changed out bolts to studs on other applications, etc.. but I have not done a head bolt change/R&R on an AMG model. I am at approximately 68K+ miles. Any DIY information or advice? Basically can I order the new style bolts and swap them out one at a time in the proper order without removing the cylinder heads? Or are there preventative measures worthwhile that one can take as ZephyrAMG is asking regarding coolant? Seems like it's putting off the inevitable to me, just do it?

average joe

I spoke with the local MB (AMG) dealer here in the uk the service manager said he has only seen 1 bolt failure so far.
I asked how they would change out the bolts and he said after lengthy discussions with other dealers they would do one bolt at a time!!!!!!
However they would only fit MB parts and therefore would not fit the ARP studs that I have waiting ( I have a Indy who is willing to do them)

Ingenieur

there are some who say the cams must be removed?

the only way to know for sure is to pull the valve covers and look

if 1 bolt at a time is possible:
loosen all bolts 1 turn or so per removal sequence to relieve tension
then replace 1 at a time in the install sequence
shouldn't be a problem

bhamg

There's no "if." Merc63 among others has shown it's possible for the M156. As to whether it's the preferred approach, in my mind I still think not.

Ingenieur

There are others who say otherwise, some are experienced techs
I don't believe anything I hear and only 1/2 of what I see
Even less on the internet

I would need to pull the covers and look
Much conflicting data

Some pics
Draw your own conclusion

Ingenieur

.....

roadtalontsi

yep cams have to come out. And no if a benz dealer does the jop and the tech isnt a hack, the head will be coming off and headgasket replaced. Non of this b.s. one at a time. It'll cost more if you have headers and those need removed in order to get the head off. Im doing mine currently, upgrading to studs and rebuilding the transmission. pistons looks pretty good for 28k and a supercharger. They cleaned up nicely.

average joe

I am still torn on weather the heads would come off. I was actually surprised when MB stated they would do it 1 at a time.

It's not a cost thing for me, it's finding the right person to do the job, who has done it before.

Like I stated earlier there are only a handful of cars that have had failures according to the dealer in the UK.

Ingenieur

there are bolts directly under the cam phasor actuators, they HAVE to be removed to access the bolts
the rest look directly under the camshaft
or at least at an angle that would make me afraid they'd snap or strip
and definitely not at an angle they could be torqued properly

I'm convinced by the pics and the comments of those more knowledgable that the cams must come out and might as well do the gaskets too

JRSJR65

Yea that's NOT what I wanted to hear roadtalontsi...I'm reversing plans to "if it ain't broke don't fix it."
Is that at work or your own shop? I may have to stop by and check it out !

average joe

I agree and to be fair might aswell do the valve buckets (m159) at the same time if the cams are coming off.

motoman

Re: prying forces on headbolt...no definitive proof. Only that everything is moving around. Likely the headbolt flanges are getting more than upward/downward movement.

Here is a survey of automotive-slanted coolant recommendations...

"8.5 to 10.5 pH optimal..."
"below 8.5 pH not acceptable ...should be 9.5 to 10.5..."
"pH balance should be 9.5 to 10.5..."
"pH levels should remain between 7.5 and 11.0..."

I will flush drain and report back with a new lab test after 60 days. Test strips apparently can be used if they are "proper" for the antifreeze type.

Ingenieur

If there were significant (negligent compared to the combustion forces and easily accounted for in those fasteners) forces in the planes perpendicular or normal to the bore they would mechanically fasten to resist them

Those 12 bolts must have 100 kip of clamping force
this is not 'sliding' or moving period
The stress is absorbed/released in the bolts, they stretch/relax in an elastic mode
But only minutely, the gasket makes up this difference

they are cyclicly stressed/relaxed at a relatively high frequency
At 6000 rpm ~ 200 Hz
But the force is small relative to the clamping force
Perhaps 30,000 lbs per combustion stroke (avg)

whoover

If it were mine I'd remove the heads and replace the gaskets. But the one-at-a-time method should be way better than nothing.

I would not loosen all the bolts. The goal is not to re-torque the head, but to replace the bolts without disturbing the joint preload and gasket compression more than absolutely necessary. The theory is that the preload of the joint as a whole will not be unduly disturbed by the removal and replacement of a single bolt.

In such an operation, tightening sequence is of no concern whatsoever. That is specified to cause the preload distribution to be as even as possible when the joint is established. But removal and reinstallation of a single bolt returns the entire joint to initial preload distribution. The joint has no "memory" of a single bolt being removed and replaced, so there is no reason to worry about which bolt to do next. This is a quite different situation than reestablishing the joint from scratch. That, with a new gasket, is always the "right" way, and then you need to follow the sequence.

Ingenieur

It can not be done 1 at a time....
Not possible

Loosening the bolt first would more closely replicate the proper process
Remove all bolts then install 1 at time
When you remove 1 bolt the head deforms
It must be reinitialized

If possible ( it is not) I would not do 1 bolt on a torqued head
It must be done on a loose or unconstrained head to push the head outward to ensure it lays flat
Can't do that if all bolts are torqued and must be in the proper sequence

If you could do 1 at a time I would torque to spec plus another 1/8 turn to compensate for the previously compressed gasket

BMW has a shop procedure for doing 1 bolt at a time
They had an issue with e30's breaking a bolt
They loosen all bolts then reinstall in sequence
They actually replace the bolt and lightly tighten
When all are done they do 2 passes to final torque
So all bolts are loose then final torqued in sequence

This is how it should be done
Say 30% while replacing then do the final stages per spec torque value and sequence
Anything else is asking for trouble
But all moot, can't do one bolt pn the M156