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.

As stated earlier, steps in The Extra Mile category won't keep your engine from running, but will help give you an edge in some manner. It may be power, improved durability, or a small handling difference for your car. These processes are not cheap, so if you are racing in a lower level class, you'll probably find more efficient ways to spend your money. If, however, you are racing in a touring series, where the competition is cut-throat, these processes may be necessary to keep up with the top cars.

Valvetrain Alignment This actually involves two steps-properly locating the cam bores and the lifter bores-but they work hand-in-hand. Earlier, we mentioned boring and honing the cam tunnel, which is done to ensure the bores are the correct size and in alignment with each other. Valvetrain alignment takes it a step further by ensuring that the camshaft centerline is the correct distance from the crank centerline. This can be off slightly on mass-produced blocks and can affect cam timing.

The correct lifter bore alignment is normally found with a B-H-J fixture, which works in much the same manner as the one that centers the cylinder bores. If a lifter bore is out of alignment, many engine builders can ream it out, insert a bushing, and then re-cut the lifter bore in the correct location. This can help in a couple of areas. First, an improved alignment between the lifter and the cam lobes helps ensure that both wear properly, which is a concern with the high spring rates being used today. Second, when a cam is designed, it is assumed that the lifters are in the correct locations. If they are off by a degree or two, they will contact the camshaft at a different point from where the designer intended and make the valve opening and closing events happen either earlier or later than intended. This, of course, is going to cost you power.

Deburr Oil Galleries The oil galleries should already be inspected and clear of any obstructions during the cleaning procedure. Examples of obstructions include metal shavings from the machining processes, casting slag, pieces of shot (if the block has been bead-blasted), and just general unidentified trash. Deburring or polishing the galleries takes things a step further. To ensure vital engine oil flows easily to the places it needs to be with a minimum of pumping effort, many engine builders buff the galleries. The easiest way to do this is with a piece of emery cloth or fine sandpaper attached to a long, thin rod. Chuck the rod up an electric drill and spin the emery cloth as you move it along the length of the gallery. If this procedure is performed, it should be done before the final block cleaning.

Lightening Lightening the block adds neither power nor durability, but it can make you faster on the track. Peter Guild says that you can easily remove 5 to 6 pounds from a standard block without sacrificing durability. This includes profiling the main gaps and grinding off unnecessary bosses. You can do some of this with a grinder, but just be aware that it's hard work for little results. Removing weight from the engine allows you to move more of it to the framerails, where you can adjust its location to improve handling, but most of what you are removing is already pretty low. It may, however, be helpful if you have trouble getting enough of your weight percentage over the rear tires.

This article assumes that you are using an unfinished block that requires machining before it is ready for assembly. Some manufacturers, such as Dart, Brodix, and World Products, offer engine blocks that are already machined. In most cases, they are machined to standard specs. Some manufacturers allow you to choose from an options list. This is a good choice if you prefer to do most of the work yourself or don't have an engine machine shop nearby. Some leave the final honing to be done in order to match your final piston size, but others prepare the engine so all you have to do is wash it and begin pre-assembly. If you choose this option, make sure you are confident in your ability to check all the critical clearances so that the parts you assemble in your block meet the correct tolerances.

SOURCE
KT Engine Development
www.ktenginedev.com