The process of align-honing the main bores ensures that the bore housing inside diameters are correct and that all the holes are perfectly aligned to eliminate excessive bearing wear on any high or low spots. A good machinist spins the block 180 degrees during the process and runs the hone through the bores in the opposite direction for a few passes.

Align-honing the main bores for the crank journals should be the first machining operation performed because every other machining operation should ideally be referenced off of the crank centerline. Since the crank isn't in the block, this point is determined by the housing bore. When this is done, the caps must be properly fitted to the block and torqued into place. It is also a good idea to have an old oil pump housing bolted into place to simulate the distortion created. This ensures that all the bores are identical and there is no droop caused by the boring bar. This procedure costs an average of $200.

Align-Bore/Hone the Cam Tunnel

The cam tunnel should be align-bored or at least honed on a new block for the same reasons that the main caps/saddles should be. Once it is correct, however, this process doesn't normally need to be done again. Unlike the main journals, where detonation can cause distortion, the cam bores don't see too much stress. On a rebuild, the cam tunnel should be honed if there is a spun cam bearing.

Many engine builders are using oversized camshafts whenever possible to reduce the chances of camshaft flex. This requires enlarging the cam bores even more than usual. The same holds true if you intend to install roller cam bearings. Honing the cam bores usually costs around $40 or so, but if you require the machinist to increase the diameter of the bore 0.010 or more, expect that price to jump closer to $75.