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Is this anything to be concerned about? I've never seen this happen to the metal on a motor before. 2007 Exige S, 5k miles.
What is causing these marks?
 

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Nein Kinder
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1,568 Posts
@Smoky - That’s an artifact of the casting process. As the aluminum is exposed to dirt and oil and it oxidizes, the small nooks and crannies trap all those things and make the surface defects more noticeable.

Glen
 

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German Reimport
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2,953 Posts
What you see is the result from an aging tool. The die cast tool used to produce these parts is probably good for 100k parts, give or take a few. The tool is made from tool steel, and every injection of molten aluminum and the following solidification will put the tool thru a hot/cold cycle. After some time, the surface of the tool will develop small cracks. These cracks fill with aluminum during the casting process, leaving the marks in the part when it is ejected from the mold. The older the tool, the more cracks you will find. Eventually the deburring process for the parts to fulfill quality specifications will be too costly. This is the point where the investment in a new tool makes financially sense, marking the end of life of the old tool.
 

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2,307 Posts
It is a sign that you car is about to spontaneously combust. I will rush right down and remove this dangerous vehicle from your property, no charge.

But seriously, I only see this on die cast parts. I wonder if it is an artifact of the mold release, or just because that is what happens to the surface from it being so smooth as it cools.
 
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