The grinding of the cylinder or engine block is fundamental and guarantees the life of the engine based on the centesimal tolerances and the roughness obtained with the subsequent operation called cylinder polishing.
The re-boring of the cylinder involves many times the increase of the diameter and therefore it is necessary to replace the pistons and the piston rings, which must be of the best brands.
During the engine overhaul phase, everything is carefully analyzed and measured with comparators and micrometers to maintain the right interference between piston and cylinder, which guarantee the tightness of the rings and minimum oil consumption as required by the manufacturers.
An overhauled and rectified engine block retains its original characteristics only when the rectification is combined with the replacement of the cylinder liners, which is nothing more than the replacement of liners, if present, or the preparation of liners where possible. Once the liners have been introduced into the worn cylinder, they are bored to bring all diameters back to the original standard with new pistons.
The block plane will then be flattened to bring the plane of contact with the head perfectly linear, to ensure a perfect seal with the head gasket.