ToXicXxX

I've never seen or heard of this before on a C63! Failing gaskets is one thing... But to have one of the bolt heads sheer right off? All the others were very loose as well.

My guess is the bolt was poorly made, and backfiring into the manifold increased the pressure enough to blow the already weakened bolt apart. I'm guessing that backfiring into the manifold was caused by my mountain run this weekend, rapidly changing elevation in my mind could have caused a series of non stoichiometric cycles .

Anyone else has this happen?

This has solved the myriad of issues my C63 has been encountering though, so in the end I'm happy b

bhamg

Damn! I'll have to check mine tomorrow. Any idea of the recommended torque?

ToXicXxX

10nm + 90° + 10°. There is a special torque pattern too.

These are ONE TIME torque bolts, they cannot be re used. DO NOT try to tighten them. They will likely break.




Torque pattern.

bhamg

Thanks!

ToXicXxX

No problem. When you check yours, do not try to tighten them, just see if they are loose or broken.

I doubt anyone else has broken bolts, I haven't heard of the problem until it hit me.

Kriston

Wow thats crazy,

Looks like an over torqued bolt.

How did you find out? Any symptoms?

abcut973

Thanks for sharing.
Can you explain the 90 degree / 10 degree thing?

CarHopper

It's like headbolts. There is a certain way to tighten bolts. It stretches the bolt to the torque to yield and also spreads out the pressure on the gasket equally.... Something along those lines I believe.

waiting for Ingeniuer to chime in with his formulas and theories.

dubzAMG

You need a torque angle gauge, or if you are using an electronic wrench,you change from newton meters to angle. 90 degrees=1/4 turn

ToXicXxX

Car started throwing codes for running lean on bank 1. I looked up the causes, and a friend of mine and the same issue stemming from loose intake manifold bolts. So I popped a socket in and just touched the wrench (no force applied, just wanted to see if they were past hand tight) to see if they were tight, and this whole side was hand loose, and the one bolt head spun around when I put the socket in it, without even trying to turn it, I then used a little grabber tool and found the bolt was broken.

I was also smelling combustion somewhat under the hood. Tested all my header bolts, they are still very tight with no evidence of gas escape.

The issue started occurring on a hard mountain run in Montana, then the codes cleared for a bit, and permanently came back after a drive to Red Deer. When I got to the shop the next day I started all sorts of testing. My idle is also somewhat erratic, it doesn't hold an RPM value but instead bounces around softly.

Bolt and gasket replacement will be done tomorrow. I'll report the results.

Looking at the end of the broken bolt, it doesn't have a pattern consistent with torsion forces, but instead looks like it was torn apart.

AMG893

Interested to know the outcome

c63beast

I had that issue... Thankfully covered by mb, it happened about a month and a half ago. No idea why.

glennhl

I second this notion!

The reason I think this is true is that the pressure loads on the intake manifold bolts are very low. However, the torque loads during installation are extremely high since these are torque to yield bolts.

Kriston

Did you remove the intake manifold to get to your header bolts?


I know you recently installed your own headers, perhaps the bolts were torqued incorrectly after re-install?

AMGer

I've had my Intake Manifold replaced by MB warranty with similar symptoms. When I asked the SA what it was they said they found it had a crack leaking pressure, but didn't mention anything about the loose bolt. I thought the problem was perhaps from the last owner of the car and maybe the CPO inspections missed this when I purchased it.

Autosport7

I just knew I was better off not clicking this thread! Now I'm all paranoid and stuff! lol

c63beast

As mentioned above, I think what happened was the garage I used hasn't worked on benzes and they basically didn't properly install it. Car went into limp mode 2-3 weeks after headers were installed.. Took it back to the shop they apparently got a quick fix for it as it came back couple months later. All in all I learned to not go to garages based on what cars they work on rather look for a specialist which I found in Austin in another shop. I would say you shouldn't worry unless you doubt who installed ur upgrades if any.

ToXicXxX

Nope. Didn't remove anything to install them, was done from the bottom up. I am also an AST (I work for a European tuning shop).

Gaskets and bolts fixed the lean issues. The gaskets were wrecked... 38,000km on them and they were severely blackened.