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As you can see from these photos, there was a lot of corrosion on these head bolts over 12 years and 87xxx miles. So it was a good thing that I change them out.
I've always said spend a few thousand now, or spend several thousand alter.
Those of you not familiar with the M156, these Head Bolts are female and due to their hollow head design didn't offer much material where it is needed. And with corrosion the top off the head would snap off, leading to engine coolant leaking into the combustion chamber.
And causing widespread damage.
The Valve Tappets looked pretty bad good for the mileage.
My tech said that these tappets, could have gone to 100K. But since your in there why not change them out.
And to be totally honest my slight valve ticking noise at start up is gone. the engine runs very quiet now.
The cam lobes showed very little wear for their mileage and age. Very surprising
They were having some issues, as they couldn't seem to find the timing marks on my performance crank pulley. But luckily they managed to find it.
And everything worked out fine.
This is definitely cheap insurance for any M156 owner, as it eliminates the worry of a failure. Granted not all head bolts have failed in these engines. But look at my nasty bolts and decide for yourself.
I'm not saying that the new head bolts might not also fail in 10 or more years from now, as these bolts are always exposed to engine coolant, as they reside in the engines water jacket.
But to mitigate the corrosive effects of the coolant, do a coolant flush and change every two years. That is just my rationale.
Yeah me too. I’ve been told my numerous sources including a friend of mine that is also a AMG Master Tech/Shop Foremen that from what they’ve seen that these old head bolts typically fail around 90,000 miles. So to save you form spending thousands in repairs, after the fact. I would recommend spending a few thousand now, than to spend several thousand later. Once the head bolts break, and you have a coolant leak, and engine coolant has mixed with your oil, the engine needs to come out to be torn down and thoroughly cleaned. And the cost about $6000-7000 especially if th heads need to be removed. So pay a little now or pay a lot later. That’s why I elected to do this as preventative maintenance.
Oh, I forgot to mention this, but after everything was done and the test drive was completed. I asked them to pull each coil packs/spark plugs and borescope each cylinder to check for any coolant leaking into the cylinders.
Everything checked out fine, been driving the car for a week now, and no issues.
If you have a high mileage AMG with a effected head bolts, then I recommend getting them changed out. Granted not all of the old head bolts have failed.
I know that all to well, but the old saying goes, pay a little now, or pay a lot more later. Replace them before they fail, for peace of mind.
Great post and pics. How are the cost or hours involved for this, please? I'm on 48k miles, so I guess I should be considering this sooner rather than later.
My shop Benz Elite Automotive had my car for 4 days, granted it truly doesn't take 4 days to do this procedure. But they wanted to take their time, and make sure everything is good to go.
The procedure was to remove one head bolt at a time, and replace it with a new one, and torque it down to spec. Thereby keeping the clamping force on the heads sealed to the block.
They examined each head bolt that came out, along with the valve tappets and cam lobes for wear/cracks etc. There is a high level of skill needed to do this job, especially when it comes time to reinstalling the cams, and setting the timing.
They preliminary quote was for $2700 out the door, but that also included installing my custom carbon fiber interior trim. So all said and done, the price was $3795 and that also included New SLS valve tappets ($900) that I insisted upon over stock, and a coolant reservoir hose.
They said that the old valve tappets showed very little wear, and didn't need replacing and should last to 100K. But why not replace them, while your already in there. And the new tappets cleared up my light ticking sound inside the motor.
And replacing that coolant reservoir hose, eliminated my low coolant issue, which I assumed was due to a possible bad head bolt. They also pressure tested the cooling system and bore scoped each cylinder for coolant leaks.
They replaced each valve cover gasket, spark plug gaskets, cam adjuster housing gaskets as part of the procedure. So this wasn't the cheap fix after all, it always seem to cost more then expected.
But like I said before, it's better to pay a few thousand in this case, then to pay several thousand later down the road. Yes, it was a little costly, but I can sleep better knowing that my head bolts have been addressed.
And there is no longer an issue of if or when.
So if your just replacing the head bolts, your cost should be around $2000-2300 including parts and your shops labor rates. My parts were purchased from VRP and Mercedes Benz https://www.vrpspeed.com/product-cat...amg-m156-6-2l/
A break down of cost:
(2) Sets of head bolts $260 x 2 = $540
(2) Sets of Valve Cover Gasket $100
(32) SLS Valve Tappets $940
(1) Engine Coolant Reservoir Hose $80
Labor $1500
Total $3160 doesn't include installing my CF Interior Trim or Taxes
How closely were the cams inspected? It is slightly difficult to tell in the pictures, but 9/10 times damaged camshafts are installed on new lifters. It looks like there is accelerated wear on the lobes shown in the pictures. Just because the lobe is not completely destroyed, does not mean it should be reused. The very top of the lobe appears worn and will damage the new lifters over time. Hopefully that is just the camera and there is no damage you can catch with your nail.
I also have a brand new set of SLS lifters for $500 if anyone else is interested in doing this job soon.
Last edited by layzie12g; Sep 26, 2019 at 08:38 PM.
This second head bolt from the left looks suspicious, look just under the bolt head. It looks like it might be cracked.
Unfortunately, I don't have these bolts to examine closely. But it really doesn't matter, as they've all been replaced.
I've been taking my cars to Benz Elite Automotive for 10 years. My guys are certified Mercedes techs, and I absolutely trust their word without question.
The cams lobes were inspected very closely, they've even provided me with a video of it. They said and we both confirmed that the cam lobes showed no signs of wear.
As that was a big concern of mine, if they needed to be replaced. Because that's an additional $2400 expense.
It is possible that the wear marks were caused by dropping these valve tappets on top of each other. Regardless, I'm very happy with the outcome, and I'm not concerned in the slightest.
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