Pistons, rings and pins are lubricated by oil thrown onto the cylinder walls from the connecting rod bearings.
Some connecting rods have oil spurt holes. These holes are positioned to receive oil from similar holes in the crankshaft. Oil can then spurt out at the point in the engine cycle when the largest area of cylinder wall is exposed. It lubricates the walls and gudgeon pin, and also cools the underside of the piston.
Oil feeds to the cylinder head, and through a gallery to the camshaft bearings and valve-train. As well as lubricating these moving parts, it also gathers heat from the engine so its temperature keeps rising.
Finally it drains back to the sump to cool, and start again.
