Block and piston both aluminum right? Same expansion generally. Very small negligible differences in thermal expansion coefficients between alloys. Likely not thermal expansion.

 

Good point.

Tuned is only a possible culprit if it’s a bad tune. Such as causing misfires. Misfires are hell on these motors.

 

I agree. Another poster suggested it. It's not entirely out of the question, but unlikely and not the leading root cause candidate in my view.

I think MB cheaped out on the coatings. It's too easy for them to do that - to cheap out on quality materials.

 

This is a fascinating discussion - love the mechanical engineering input

 

I think the theory is that in cold climates, during the first few minutes of combustion, the piston (aluminum) which has a low mass relative to the cylinder wall (also aluminum but more mass and backed by cold coolant) and cylinder head will heat and expand faster in the first few minutes of operation. In an engine with tighter tolerances this will lead to friction/wear. The Porsche forums are full of talk on this subject. Apparently the scoring problem is dramatically more pronounced in cars that are run in colder climates. Plenty of all aluminum engines run in northern areas without this problem so not sure myself....

 

Car is very well - still gets more comments than any other car I ever owned, and NONE of the negatives. For the casual observer - Mercedes station wagon with flat, crappy paint. For the insiders....
Funny thing is that in the young crowd (15-25) i get a LOT of thumbs-ups or the "wow - is that a E63 wagon?" (the car is debadged) - there is hope for the next generation!

Brackets are phreaking perfect - both on this and the other set for the BMW you made. Had one more save in the last 3 months. Heading to Home Depot at 7 AM, spirited driving.....

One more year of warranty left, then a TCU tune and then a ECU tune. Will be 100% to talk to you first.

 

Love it!!

 

I hadn’t considered the uneven cooling aspect between the the piston and cylinder wall do to cooling water jackets in the block. This has some merit. However, some folks forget that the rings are designed to accommodate this as they actually ride on the wall and not the piston itself. So because of this I would still argue that thermal expansion is probably not the problem.

with that said, the cooler climate cars may indeed still have a tougher time with ring to cylinder wear.

 

With that also explain why frequent short trips without letting the engine get up to temperature would also be deleterious to this M157 engine?

 

So the rings on a piston are basically springs with a split in them. Typically about 1/2 to 1 cm. If you ever hold a piston and ring in its piston groove you can squeeze the ring inward reducing its diameter. When you build a motor, as I have a couple of times you use a tool that compresses the ring diameter enough to install the piston assembly into the bore. When you then pull the sleeve tool out you are left with a spring preload against the cylinder wall.

because of the ring gap mentioned you always have the multiple rings on the piston clocked differently such that these gaps don’t line up to hold compression, disburse oil evenly, and to have even surface loading on the cylinder wall.

So to best answer your question, at least on my end, is that frequent “temp cycling” is going to have that ring preload vary a bit. There is of course a “sweet spot” preload that is designed in at steady state operation. So while, hammering the motor when cold won’t immediately reck the motor, it does put more stress on the cylinder wall. Almost all engine wear before it becomes problematic is a cumulative effect over many temp cycles and miles. So it stands to reason that we should go easy on them until reaching that minimum oil temp of 159 when the reading changes from blue to white.

This might be common knowledge to many of you guys. But it has been my experience with other fellow ME’s that have not actually built a motor themselves, that they are enlightened when seeing these specifics so thought I would share.

FWIW. 😁

 

very good stuff

 

Piston differential expansion vs the block is a candidate in my mind. Smaller piston mass and direct exposure to combustion gases means it heats up faster than the block with has much higher mass, less direct combustion gas exposure and in a cold start is chilled by potentially -40degF coolant in February in Calgary.

Lets also not leave out oiling. Oil coverage for #5 should not be assumed to be identical to other cylinders. Same comment with coolant flow to #5. Each cylinder has an ever so slight difference in conditions. Oil supply that for whatever reason falls a bit low in the tolerance range would create higher temps and friction in the contact point between piston and cylinder.

Add all of the above to pistons and bores potentially at the edges of their respective diameter tolerance ranges, and MB cheaping out on surface coating materials and it’s easy to see how scuffing could occur.

I think the root cause is MB cheaping out on coatings.

 

I agree that it may be a bunch factors adding up to a problem. That shop in the UAE who posts a bunch of rebuild videos of m157 engines complains about how soft the cylinder wall coating is, he even uses a screwdriver to demonstrate how easy it is to scratch through.
Oiling would certainly explain why #1 & 5 suffer first. Not so sure about the turbo placement theory I've seen mentioned. The cast iron turbo housing will certainly stay hotter longer after shut down but there is a reasonable air gap between it and the outside of the block, not to mention 2 aluminum walls and a water jacket....

Besides tight tolerances between the piston and cylinder, there are other design parameters such as piston skirt length relative to piston diameter that play into the side wall loading of the piston during portions of the power stroke.
Also wondering about possible damage from chunks of loose carbon being trapped above the top compression ring between the cylinder wall and piston crown. I got the below picture yesterday. the missing piece of carbon was there last week....wonder if it did any damage on the way out....
About 7 or 8 years ago I was thinking of buying a Porsche 911 of some sort, back then the only thing you heard about was the IMF bearing issue, fast forward to now and you are seeing this cylinder scoring issue as a big deal. I'm hoping in a few years the M157 engine isn't seeing similar problems

 

Cylinder scoring across manufacturers suggests common cause between them, especially during similar time eras and geographies (Germany). Cylinder lining chemistry is easily one of the potential common causes between MB and Porsche. Manufacturers catch wind of the latest unobtanium to coat the cylinders and other manufacturers drink the Kool Aid. Then they discover how expensive it is and specify too little coating material to get the job done properly.

Nikasil
Nanoslide
etc.

It all sounds pretty snazzy during the advanced engineering phase. Then when cost needs to be cut leading up to production, the magic juice is at the top of the list for cost cutting.

 

When they "HAND MAKE" the AMG engines does the tech measure parts and time the cams etc like a good engine builder would?

or do they just grab parts and assemble and hope the engineers got the design right and hence the drawings/specs and hence the part TOLERANCES correct.

And then the tech hopes the part suppliers actually got the correct drawing/spec latest revision level and then made them to meet spec?

And then the tech hopes the QC department did their job and ensure all parts did in fact meet spec.

What parts does MB sub out?


Or do they just whip out 10 engines a day?

 

I'm pretty sure the managers drive around and pick up random day-laborers to assemble the engines. It's a miracle if they last over about 10k miles.

 

Perhaps take a at this video. Will likely answer most of your questions. There others that are readily accessible.

CAR FACTORY : MERCEDES-AMG V8 ENGINE ASSEMBLY l AFFALTERBACH - YouTube

 

Why don't you consider a different car? One that would check all the boxes for you?

 

it was a sarcastic response to a ridiculous post. @billvp218 was in no way being serious...

 

Imagine owning a f10
But in all seriousness, wish MB had spent extra on con-rods and cylinder walls.

 

touche

 

So today's the day, picking up the car this morning. SF Benz got the new motor installed under the warranty limit (as others suggested I pressure them to do - thank you) and took care of a suspension creak issue under the warranty limit, as well (another $1500). They apparently had no problem finding about $6K of wiggle room in their original estimates. I got text notifications of three very large credit card payments by the warranty company that posted yesterday, they definitely paid full freight on this.

As I told the warranty company after they refused to work with me on a cash payout or buy the car: I would not spend $64K of my own money to do this fix, but I will spend $64K of your money to do it. So here we are - a 2015 wagon with a zero mile motor and a fully exhausted aftermarket warranty.

Thanks all for chiming in. This thread has been a wild ride.

 

I've seen cylinder scuffing/scoring like that on a few different cars over the years. One thing that has been common amongst a few of them it that the cars were driven pretty hard from the get go....rather than letting the water/oil temp get somewhere near normal before hard acceleration or using all the revs and giving the motor time to even out expansion rates......some cars (especially those with coated bores (M156 M157 for example)) are more sensitive to that than old style steel sleeved motors. Just my two cents.....and of course I have no evidence that the cars mentioned above where ever treated with anything other than the greatest mechanical sympathy!!

 

mechanical sympathy!!! Love it !!!

 

I agree and seen this aswell.

Glad it worked out for the OP via warranty.