GT-ER

That is absolutely a fueling AND/OR ignition timing problem. I've seen this kind of damage a million times from knock. Since it was number 8 and people here seem to normally pop number 8, than I can assume that the problem is fueling over timing. But that is not a failure that occurred just because the part was defective or something like that.

jumpinjack

GT-ER,
Is this an octane issue or fuel deliverly to cylinder issue when you say above "fueling and/or ignition timing" problem? Just wondering. Thanks

AMG_RL

Agreed. jumpinjack it's most likely caused the inferior design of the stock fuel rails not being able to deliver fuel to the #8 cylinder causing a lean mixture. not usually a big problem on stock cars, but on modded cars running higher boost it definately comes into play as the OP did note that he was doing a number of WOT pulls.

aghakauve

Ouch that looks bad! Hope everything goes well for you, keep us updated

AUS-E55

Ok i could be wrong but it just looks like too clean of a brake, it just doesn't look like any other number 8 piston failures I've ever seen on these motors, didn't benz_addict just replace this piston with a used one ?? was piston to bore clearance checked when the motor was reassembled,

Yacht Master

Oh Ouch, don't worry it can be fixed, chin up.
I would replace the head though, warped aluminum heads after a thermal and mechanical (fod) event, even resurfaced never stop warping, you should be able to find a good used one. Head bolts and threads in block need to be checked before replacement head gets torqued.
From what I see your cylinder looks serviceable, I think you may have lucked out.

for those that have not read the Head thread,
https://mbworld.org/forums/w211-amg/...pped-head.html

jumpinjack

Thanks for the followup.

sneakyneon

Detonation(knock) is what cause's the damage, It may be due to a few diffrent things, An engine that is to lean will have detonation, a car with to much timimg for the octane used with detonate, Increase engine temps with lower the threshold, hot spark plug heat range, sharp edges in the cumbustion area. so on so forth.

GT-ER

By that I mean lack of fuel ( or too high an air to fuel ratio ) OR the ignition timing is too advanced for the octane being used. In any case, I'd bet my money of fueling. Although he apparently had replaced piston 6 a while back which could mean that the timing is the actual culprit, although timing issues tends to leave pitting on the pistons and the pistons look fine ( except the one that blew but the pitting on that one is because of the ring land bouncing a billion times inside the chamber ) . He's going to have to rebuild and retune to find out.

AMG_RL

Idk with detonation if one of the valves was to hit the piston like it seems it did, I've seen similar kind of breaks in other kinds of engines.

GT-ER

If the valve hits the piston it'll mark it but I can't see and marks on the piston.

ejsheltra

That piece probably did not explode to a million pieces but may have done seat and cat damage depending upon velocity out. Are the valves bent? What about the bottom end?

GT-ER

It bent the exhaust valve from what I can see. It probably just broke into smaller chunks before escaping the chamber through the exhaust valve, damaging it in the process.

AMG_RL

ahhh good catch looking at the pics again you are right.

benz_addict

piston is out


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I'll have to hone the walls there's a deep scratch. I'll also need fatter rings hmm

GT-ER

How deep a scratch? I would just do a VERY FINE honing to smooth it out ever so slightly without eating up too much material. Obviously pics aren't the same as having the sleeve in front of you but that sleeve doesn't look bad at all from that pic. You should check for roundness though.

benz_addict

Thanks for the reply I was thinking about honing it just ever so slightly so even out the surface. But just one deep scratch is I'm worried about...

GT-ER

You'd be surprised how little a scratch will affect performance and durability. It's not ideal, but compared to the options it's pretty much the only option that's acceptable. I've replaced pistons on engine with old used rings and without even cleaning the sleeve wall from dirt, particles and scratches and they've worked great. AMG's aren't any different.

Tech-Tune

Surprisingly your cylinder wall looks to be in great shape.
The scratch that you mentioned, are you referring to the straight dark line that is visible in the picture (bottom left)?

03'55AMG

Yea, looks good here too, more pics of scratch?

TopEndS62

light honing would do the trick... not a bad time for piston upgrades...if the budget allows of course

benz_addict

my finger nail is getting *caught* in that 1 deep scratch rest of the wall looks smooth. What if I don't hone it?



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GT-ER

I suggest you hone it because the scratch may have a small lip ( microscopic ) that may cut slightly into your ring and wear it down too quick. I quick honing will eliminate any lip the scratch may have. You don't have to ELIMINATE the scratch though, it's not a big deal.

03'55AMG

+1, just get rid of any lip ity may have. I doubt youll even notice, besides maybe some drop in compression.

AMGPilot

Have you ever built an engine? Do you have ANY experience other than what you've read on the web? Once again that is some bad info