In light-duty applications, pistons within the cylinders are designed with aluminium or cast iron, and are in constant direct contact with the cylinder bore whilst in operation. Some scratching on the outer surface of the piston poses no risk to the cylinder’s function, as long as the nominal bore diameter does not exceed the minimum diameter of the piston. A good tool to use to check the length could be a micrometer.
the piston seal can become defective if it is distorted, eroded or missing and this is usually a cause of an oversized barrel or bulge during operation. At this point, replacement of the barrel or cylinder is required. If you replace the piston seal only and not the barrel, whilst this is a quicker method of repair, it is a short-term fix. More maintenance would be required later on.
In most cases, the chrome on the rod can be inspected and if it is shiny on one side and dull on the other, the rod is bent. The straightness of the rod should always be checked when repairing the cylinder. Bent rods can be corrected by using a press. Whilst it is possible to prevent damage to the hard-chrome plating during this process, if the chrome is spoiled, it must either be re-chromed or the entire cylinder must be replaced. A damaged chrome surface decreases the efficiency and service life of the rod seals. If the rod only has some minor scratches, they can be polished out using fine emery paper.
A distorted rod seal can be caused by excessive wear of the guide bush or if the rod is bent. The consequence of this is the rod weight pushing on the seal, causing failure. If you replace the rod seal without identifying and correcting the underlying issues, then again, the fix will only be short-term.