AMC63

Hi everyone,

Have a unique situation that's popped up and was looking for some advice.
Decided to be preventitive and replace my headbolts on my 09 c63 @ 130,000km. I drive it approximately 1,000km a year, basically weekend driver since I have a company vehicle.

Anyway completed the passenger side bank , installed new bolts, cams, lifters and all necessary hardware even addressed the cam adjuster plates. Old head bolts were in mint condition! I expected to see some sort of corrosion but they had none at all.
Moved on to the driver side and all was going well till I got to bolt #10.... I noticed a line running through the top of the bolt , turns out the bolt was stretched and and the head of the bolt was seperating.
Decided since I've gone this far to attempt removing, I managed to turn and remove the bolt . Of course not nearly as much torque to remove it since it had stretched out.
I usually see situations where the bolt head is already broken off or they break trying to remove.

My question is since I've gotten to this point do I just try and finish up and do a coolant pressure test and cross my fingers????
I never really noticed any coolant loss before but that could be also that I drive it so little.

Any advice would be great.

Thanks,
Adrian

Stretched bolt

All the other bolts looked like this

chrisridebike8

I think you got very lucky. I’d say bolt it back up and run it. If you didn’t have misfires or coolant loss, you were probably fine-ish.

BLKROKT

Man that’s a close call. I’d agree with Chris. Call yourself lucky and get it back together. You’re likely fine.

Jasonoff

Did you verify there's no coolant entering the combustion chamber pre bolt swap?

That rear inside bolt probably has the most amount of gasket surface area so hopefully got lucky.

AMC63

Thanks guys , makes me feel a little better !
I checked the cylinder/piston to see if it had been washed out by coolant and thankfully it hasn't.
Not a guarantee but whenever I've seen head gasket leaks pistons usually polished.
All I guess I can do now is perform pressure test on cooling system and inpsect for leaks. The fact that I have only done 3500km since 2017 might have helped .

Oil that was removed from pan was spotless and didnt notice traces of water thankfully. I should have sent the oil out to be tested however I dumped it before discovering the bolt.

Bolt that stretched out

Top of piston next to that bolt

Jasonoff

That picture you posted is the right side and the bolt circled is #8. EDIT: Looks like the bolt numbers are flipped in that pic actually. Likely not a problem if you used that torque sequence though.

Bolt numbers are mirrored for the left side.

AMC63

You're absolutely right.
Since " #8 " had stretched I had no choice but to replace it first and disrupt the sequence.
I figured the sequence didn't matter all too much at that point.
Realistically in my opinion I don't think going in sequence even matters with the 1 bolt at a time method, but that's just my opinion anyway.

swedepat

If engine cold and loosening bolts, there are actually no need to follow any sequence.