Definition of Line Boringby Moss Strohem
Line boring -- sometimes called "align" boring -- is an engine machining process that establishes perfectly straight bores for crankshaft and camshaft housings (also known as tunnels or saddles). It is the most essential step in "blue-printing" an engine block.
Reasons for Line Boring
The tunnels or saddles, which crankshafts and cams rotate in, need to be straight in order to avoid damage. If the housing is not straight, it will cause the rotating part to bend/flex with each revolution. This is a common procedure in engine rebuilding. Establishing the correct crank center-line is critical since other machine processes are based off that line.
How It's Done
Crankshaft bores are carefully measured for correct diameter and alignment. When not within recommended tolerances, an engine block is placed in a fixture and a long boring bar with a cutter is run through the entire length of the bores to renew straightness and roundness.
The boring (cutting) process is the first of two steps. Boring gets the bores to an approximate rough-dimension. Bore honing is a much more precise process that uses stones instead of cutters to finish-size the bores.