Precision Align Bore and Cylinder Honing By Eddies Performance

All Eddies performance and racing engines that go through our machine shop go through a precision align bore and cylinder honing process. This ensures that the pistons and rotating assemblies run true while the engine is running, not only in the block cylinder but also relative to the center of the crankshaft. This process includes align bore to the main bearings and the camshaft and crankshaft to ensure they run true and friction free as well.

If the engine boring is at any kind of angle not relative to the crankshaft, engine failure could occur. To prevent this, Eddies Performance utilizes a careful quality control process that ensures and inspects all blocks for cylinder wall tapers, out of round diameters, cracks, camshaft and crankshaft misalignment. Due to the magnitude of this process, align bore and honing can only be done by very experienced machine shops such as Eddies.

Provided that the block has passed quality control processes, we then determine what is needed to customize the engine block. The block is then cleaned in the tank and if the block is used, we then magnaflux to inspect for any cracks or possible surface issues. Then the block goes through another quality control process called check line bore then to cylinder honing.

If a block is being align honed, the bushings that support the cylinder honing bar are usually mounted in the undamaged end journals of the block. Centering pins in the middle of the bar are used to center the bar in the center main bore. Stock removal from boring is usually limited to about .002" or less when cylinder honing.

Big Block Chevy Going Through The Boring Process

With line boring equipment, pilots are used to position the bar. This allows faster stock removal and does not usually require any oil or lubricant. Changing the position of the bar will change the centerline of the bores and crankshaft.

Many engines can handle a few thousandths variation in the position of the crankshaft centerline but others cannot because of changes it causes in other critical dimensions such as the deck height of the pistons when the crank is at top dead center (which affects compression, piston-to-head clearance and valve-to-piston clearance). Performance engines and diesels are much more sensitive to centerline changes than light duty passenger car engines.

Because main bore alignment is so important, it is the first step that we machine on any engine block. This the most important step we commit to and it must be done accurately because most of the other critical dimensions center off the crankshaft.

Align Bore Crankshaft and Camshaft

There are three basic reasons for boring the main bearing and cam bearing bores in engine blocks. One is to restore worn, out-of-round or damaged bores. If an engine overheats or loses oil pressure, one or more bearings on the crankshaft or camshaft may seize and spin. 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.

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.

In the case of worn, out-of-round or damaged cam bearings in an engine block, there are no removable caps. The only option is to enlarge the bores so new oversize cam bearings with a larger outside diameter (OD) can be installed.

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). As rigid as an engine block might seem, there is actually quite a bit of residual stress in most castings. 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. This affects the alignment of the crankshaft and camshaft bores as well as cylinders. Eventually things settle down and the block becomes more or less stable (a "seasoned" block). The bearings as well as the crankshaft and camshaft journals gradually develop wear patterns that compensate for the distortion that has taken place.

Additional warpage can occur if the engine is subjected to extreme stress (like racing) or overheats. If the original crankshaft or camshaft is then replaced without align boring the block, it may bind or cause rapid bearing wear. Likewise, if you're building a high performance engine with close tolerances, you don't want any misalignment in the main bores or cam bores.

The third reason for line boring or honing a block is to correct or change bore centers or bore alignment (as when "blueprinting" a high performance engine). The camshaft and crankshaft should be parallel in the block. If they are not, line boring can correct the misalignment to restore the proper geometry. With performance engines, there may also be a reason to change the centerline of the crankshaft or camshaft slightly to alter the piston or valvetrain geometry.

Line boring will also be required if the original main bearing caps are replaced with stronger aftermarket caps, or the block is being converted from two bolt main caps to four bolt main caps. For best results Eddies finds that four-bolt main caps should be machined in three-steps. First, we bore the housings to within .030" of the desired size. Then bore again to within .005" of final size, and finish to size by align honing. Harder honing stones work best on cast iron while softer stones (such as J45 silicon carbide #150 grit) do better on bimetal applications where the block is aluminum and the main caps are cast iron, steel or powdered metal.

---

Quality Control With Your Engine Is Our #1 Priority

At Eddies Performance quality control is an important factor in our customer experience. Careful measures in checking and double checking clearances is our precedence in producing a fast, reliable engine that will bear our responsibility.

If you would like to discuss your application please give us a call on our toll free number 1-800-471-2325 from 9am to 5pm EST.