Pure guess on my part cause I never wanted to be a spurt anyway but I'll say the watercooled needs looser tolerances because the cylinder will not expand but the piston will. #2 For aircooled engine only. The cylinder needs to "learn" how much the piston needs to expand. Not all parts will expand evanly (all you have to really worrry about is not overheating) #3 Havn't a clue. #4 I haven't seen one with a tapered/recessed toplike a large diesel has , so I say all the side surfaces. Allowing for lubricants of course. #5 It doesn't. The ring. Not since about 1930 ad. Unless we're talking about CI sleeve liners. #6 Squish band if present and slicking the cross hatch rough spots.

All surttulation on my part.

After rebuilding a dozer/tractor engine I try to push a pile of dirt wide open up hill if there's one close by as soon as possible. Just have to cool it down slowly afterwards and it's good to go.