Cylinder re-boring is required after a seizure, excessive wear or overheating. Metal is removed to ensure the cylinder is both round and parallel throughout its length.

Over sized pistons are then required to take up the difference that the boring created. Pistons are usually but not always available in the following sizes: Standard (std) +.25mm, +.5mm, +.75mm +1mm. If your cylinder block is damaged or worn beyond the oversize available for your engine then the block will require re-sleeving or linering back to standard size or a size that a suitable piston is available.