1mm piston

It is a possibility that the stuff that was forming was because the truck ran cold for such a long time i have seen it before but never bothered to figure out y to tell u the truth please let me know y it was happening when u do figure out

 

Does your Air compressor Air supply come from the front of the head?
Looking at #1 liner is shows areas of Carbon packing on the Margin above the top ring which wipes the Liner bore clean as can be seen in the Picture.. The large amount of Carbon on the piston crowns show you have a issue. Once the Carbon Packs out on the top Margin it starts to transfer heat to the piston as its tight in the bore with the carbon reducing the Piston to Bore clearance hence no carbon on places at the top of the liner.