Rebore

Rebore is the process of enlarging an existing bore, typically a cylinder bore in engines, to restore dimensions, roundness, and surface quality after wear or damage. The term is used especially in automotive and industrial contexts, and it may be written as rebore or reboring.

In practice, rebore begins with precise measurement of the current bore using bore gauges and micrometers. A suitable oversize is selected (for example, +0.010 inch or +0.020 inch), and a precision boring operation is performed with a boring machine or a carbide-tipped reamer to remove material evenly from the bore. After boring, the bore is usually honed to achieve the required surface finish and cross-hatch pattern that aids piston ring seating. Final sizing and tolerances are verified to specification, and a proper lubrication film is considered for break-in.

Rebore is commonly used in internal combustion engine rebuilding to restore proper bore diameter and concentricity. It may also be applied to hydraulic and pneumatic cylinders, or other cylindrical bores in industrial machinery. When wear is extensive or bore walls are thin, sleeving (inserting a new cylinder liner) may be preferred over rebore to preserve material integrity.

Tools and equipment involved include boring machines or CNC boring centers, boring bars, honing equipment, bore gauges, micrometers, and appropriate cutting tools. Materials such as cast iron, aluminum, and alloy liners require different speeds, feeds, and cooling strategies to avoid distortion or glazing.

Overall, rebore is a restoration technique aimed at extending the life of a bore by returning it to specified dimensions and surface conditions, often followed by honing and, if needed, sleeving.