Before installing new 
Piston rings, check the end gaps and lay out each piston set with a piston/connecting rod assembly, keeping them together as a matched set. Insert the top compression ring into the first cylinder, squaring it with the cylinder walls by pushing it in with the top of the piston, ensuring the ring is near the bottom of the cylinder at the lower limit of ring travel. To measure the end gap, slip feeler gauges between the ends of the ring until a gauge equal to the gap width is found; the feeler gauge should slide between the ring ends with slight drag. Compare the measurement to the specified value, and if the gap is incorrect, double-check the rings. For used rings, have the cylinder bores checked by a specialist to determine wear and seek advice on the best course of action. If the end gap is too small, carefully file the ring ends with a fine file; if too large, check the dimensions of all components and new parts. Repeat the procedure for each ring in the first cylinder and the remaining cylinders, ensuring rings, pistons, and cylinders remain matched. Install the piston rings using marks or notes made during removal for original groove placement, and ensure new rings have their top surfaces marked facing up. The oil control ring should be installed first, composed of three elements: slip the spacer/expander into the groove, then install the lower side rail without using a piston ring installation tool to avoid damage, and finally install the upper side rail in the same manner. After installing the oil ring components, check that both side rails can turn smoothly in the ring groove. Next, install the second compression ring followed by the top compression ring, ensuring their marks face up and avoiding unnecessary expansion. With all rings in position, space the ring gaps uniformly around the piston at 120 degrees intervals, and repeat the procedure for the remaining pistons and rings.