Got myself new toy

 

I want your expert opinion about this damage. I will let you know later real reasons, just want to know your technical level.
Here is the damage. Block less than 40k miles by the way.

 

Far from being an expert, but my guess would be carbon build-up on the pistons. Given that all cylinders are affected - bad turbo?

 

Nope. Any other version?

 

Timing off due to bad chain tensioners?

 

Nope. That is an outcome of Stage 1 Stage 2 boost on stock engine..
And this is an explanation. This is open deck design where top of the cylinder is not supported by block. When some one increases turbo boost beyond engine design your cylinder start flexing into oval shape. The blue arrows are cylinder expansion direction. Because of tensile strength of cylinder material cylinder walls contract in the direction of red arrow as much as they could. And that is the problem because there is a weak point between cylinders shown in green - water cooling ducts. Those wear points along water cooling ducts are result of squeeze - similar to breaking lines you see when squeeze beer can. The purple arrow is a point of maximum contraction under the boost where your cylinder is squeezed so much in that direction that you start pushing on piston crown (which is very narrow in nature so you can imagine how tight things become). As a result you start scraping your piston on the opposite side of the push point shown in yellow ovals.
Now you know that happens to 60k dollars engine when you buy 1k program.
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Will say it looks like a bad head gasket and failure of the piston skirt coating.

 

I already gave an explanation. Failure of gasket on both sides of block has very little probability. Skirt coating usually damage base of the cylinder where in this case base of cylinder has no wear.
Bore dial will show you residual oval shape in cylinder. But i don't really need it to measure since i already know the reason.

 

Thanks for the detailed explanation. Makes sense.

 

the m156/157 engines are awesome, they are already missed and will be coveted in years to come. Newer M140 is cool, but not the basic motor the 156/157 is.