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[Wheaters]

Possibly a manufacturing defect, but it looks like there’s rust present.

If there’s a problem, it’s possible that a rebore might remove the marks.

Lightning strike?

[trophyvase]

There seems on the photo to be a close match between the colour of the marks down the barrel with the colour of the rim at the bottom of the carbon circle at the top of the barrel.

If there is any actual connection between these two deposits I have no idea what it may be!
Those marks down the barrel it seems to me must be more than surface deep.

It would be helpful to see the main thrust face of the piston - which I think is the segment of the barrel surface along which these marks have occurred.

[Bullet Whisperer]

Perhaps you had something nasty in your oil? Those marks are in line with where most of the oil would be flung from the big end as the engine spins.