Photo's of my cracked piston SL55 AMG, any expert opinions? - Mercedes-Benz Forum

 
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post #1 of 7 (permalink) Old 07-09-2012, 06:50 PM Thread Starter
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Photo's of my cracked piston SL55 AMG, any expert opinions?

Hi all. The guys over at Pistonheads suggested I should post here and ask your views on my piston problem

About 2 weeks ago my car (SL55 AMG, 2002, 96k miles, unmodified, FMSH) developed a misfire which I thought would perhaps be a coil pack or something simple. My local Mercedes dealer diagnosed low compression on cylinder 7, and after further investigation discovered that the piston had cracked in half which is apparently unheard of on these engines.

I'll post up some pics of the cracked piston below. It's actually cracked right across the face (which is 9mm thick) down the sides and across the underneath of the face, including the tops of the holes for the gudgeon pin. The only part that doesn't show any visible crack is the underneath of the pin holes.

I wondered if there are any engineers about? Your opinions would be welcome Is it likely to be a one off event caused by a slight fault from manufacture? Or what other reason could have caused it? I could perhaps understand it if the car had been running on increased boost and a remap, but it's always been completely standard and meticulously serviced by Mercedes in Weston Super Mare.

Some people have suggested that AMG would want to see the piston to try and diagnose the problem, so I emailed them at "marketing-amg@daimler.com" but haven't recieved any reply - does anyone know if that's the correct email address?

Thanks!





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post #2 of 7 (permalink) Old 07-09-2012, 06:51 PM Thread Starter
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post #3 of 7 (permalink) Old 07-12-2012, 05:46 AM
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Do you recall if there was any pinging noise coming from the engine just before the problem? Low octane gas certainly would lead to pre-detonation, and piston/valve failure in high-compression motors.
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post #4 of 7 (permalink) Old 07-19-2012, 07:10 PM Thread Starter
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Thanks for the reply Andrzejek.

No there was no detonation or pinging, it runs standard boost on 99 ron fuel.

The general opinion from mechanics so far is that it's probably a manufacturing fault.

Had some good news today, Mercedes have opened a case file in order to investigate further, so we'll see where that leads.

I've got a thread running on PistonHeads for future updates and the outcome (if anyone finds this in the future via the search function) as there doesn't seem to be any interest over here.
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post #5 of 7 (permalink) Old 07-19-2012, 08:45 PM
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My bet it's a flaw. Lucky it did not have complete failure. Never seen anything like it before.
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post #6 of 7 (permalink) Old 08-09-2012, 10:48 AM
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I have rebuilt alot of engines thru the years and I have never seen anything like that . I would have to think that it is a manufactureing defect. The amazing thing is that it has lasted this long.
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post #7 of 7 (permalink) Old 08-12-2012, 06:53 PM
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I'm not an expert BUT!

This is some kind of manufacturing issue with this piston, the extent of the crack and still operating is proof the car has not been beaten. Under a few high RPM runs this piston would have been found either in the oil pan or a connecting rod would be sitting out in open air, if you know what I mean. Don't back down from MB stand firm with the belief that it is their problem and for good measure insist on all pistons being replaced. Insist MB look into codes or faults within the electronics to prove your point and extract any info from the cars control module.
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