Cylinder block line boring is part of the machining of engine blocks. . When defects occur in the main bearing housing of the engine block, such defects can be repaired by line boring. Line bearing preparation begins with straightening the brackets or cover of the main bearing housing and straightening the seats on the engine block to reduce the diameter of the housing. As the diameter is reduced, the engine block is placed on the machine and a machine rod carrying a drilling cut is inserted into the gallery of the main bearing housing. It is necessary to measure the optimum hole diameter so that it is within parameters after line boring.

Some engines on the market have main bearings which are oversized on the outside to simplify preparation for line boring and avoid the aligning of the dowel surfaces, which is a more suitable option for the geometry of the main bearing housing bore.

For more severe defects (seizure) of the main bearing housing, where line boring alone is insufficient, we apply the material by welding and then perform line boring. A similar procedure is used to repair damage to the main bearing housing at the axial seat.