Bore alignment is an important process during engine machining. It establishes a perfectly straight bore in the crankcase and cylinder block. Bore alignment and measurement are vital tasks for any application.

WHY IS MAIN BORE ALIGNMENT IMPORTANT?

Alignment of the main bores plays an important role because its position establishes the centerline for the crankshaft, and how the crank aligns with the cylinder heads, decks, and camshafts. If the bores are not aligned properly, the main bearings can usually be machined or honed to restore alignment and size.

CYLINDER BLOCK LINE BORE ALIGNMENT

When referring to cylinder heads, the term line boring refers to the main bearing housin­gs but it can equally refer to camshaft housin­gs where the camshaft is located inside the cylinder head. The line boring operation restores both the size and alignment of these hous­ings so that the rotating components (cams or cranks) turn freely.

With cylinder blocks, one of the most common reasons for needing a line bore is after a crankshaft has failed. A badly worn cranking shaft can “whip” within the main bearing housing distorting them. A seized crankset (due to lack of lubrication or pressure) can result in the chainrings locking into place on the crankset resulting in them being forcibly turned by the chainring teeth which causes distortion and wear.

Similarly, if a seizure occurs inside the camshaft housing where the cam bushes are located, they could be damaged or even rotate within the block itself, causing serious damage. This could result in damage to the housing which would require the housers to be bored oversized, removing the damage and realigning them. Corresponding oversized bushes will be needed to completely repair the damage.

In high-performance vehicles, strength in the cranking shaft area can be improved by installing steel main bearing caps. These will be provided in a semi-finished state and may require some line boring to ensure perfect final alignment before installation.

All or any of the above could mean that your casting needs to be line bored.