With cylinder blocks the most frequent reason to need a line bore is following a crankshaft failure. A badly worn crankshaft can “whip” within the main bearing housings which causes distortion within them. A seized crankshaft (through lack of oil or pressure) can cause the shell bearings to lock onto the crankshaft resulting in them being forcibly rotated within their housings causing both distortion and wear.

Equally, if a seizure occurs within the camshaft housing the cam bushes may be damaged or in extreme cases might rotate within the block itself. This can result in damage to the block which would require the housings to be bored oversize, removing the damage and correcting the alignment. Corresponding oversize bushes will be needed to fully repair the damage.

In high performance engines strength in the crankshaft area can be improved by fitting steel main bearing caps. These will be supplied in a semi-finished condition and line boring will be necessary to ensure perfect final alignment.