This affects the alignment of the crankshaft and camshaft bores as well as cylinders. As a new 'green' block ages and undergoes repeated thermal cycles, the residual stresses left over from the original casting process tend to distort and warp the engine. As rigid as an engine block might seem, there is actually quite a bit of residual stress in most castings.

Reason number two for line boring a block is to restore proper bore alignment – a process which is often called 'align' boring (or honing if a line hone is used instead of a boring bar). The only option is to enlarge the bores so new oversize cam bearings with a larger outside diameter (OD) can be installed. In the case of worn, out-of-round or damaged cam bearings in an engine block, there are no removable caps. With main bearings, a worn, out-of-round or damaged bore can be restored back to standard ID by grinding or milling the mounting surface of the main caps, bolting the caps back on the block, and then cutting the holes back to their original dimensions. The resulting damage to the bearing bore must then be repaired by either machining the hole to accept a standard sized bearing or an oversized bearing. If an engine overheats or loses oil pressure, one or more bearings on the crankshaft or camshaft may seize and spin. One is to restore worn, out-of-round or damaged bores. There are three basic reasons for line boring the main bearing and cam bearing bores in engine blocks. Line honing typically removes less stock and leaves a smoother finish than line boring, making it well suited for applications where only minimal stock removal is necessary or where a smoother bore finish is desired or required (as in overhead cam cylinder heads where the cam journals have no bearing shells or inserts). A hone uses abrasive stones rather than cutters to remove metal. The bar is then turned and advanced to shave metal off the inside of the bores so the inside diameter (ID) of the bores can be resized to the desired dimensions (back to standard size or to oversize).Īn alternate method for machining the bores is to use a line hone.

A horizontal boring bar with cutters mounted on it is inserted into the block and then centered in the main bearing or cam bearing bores with support bushings or fixturing.

Vw line bore tool