Originally Posted By: Silk
This is a Mitsubishi 4M40 - the 2.8 diesel.I've never seen inside one to see what causes these marks on the bore,but they all have it.Even the new 4M41,that is the 3.2 direct injection common rail version.Their other small diesel the 2.5 4D56 doesn't do this.
I think Mitsubishi laser etched certain cylinders for oil retention reasons. I'm not 100% sure that what we are seeing here, but, I'd bet a dollar.
Years ago, Mitsubishi pioneered a system where cylinders were laser etched in specific patterns. The etching produced deep, uniform, microscopic oil retention pores. The result was greatly reduced cylinder wear, especially towards the end of engine life, at the point wear accelerates.