A bipolar nut case featuring the diametrically opposed personalities of Master P and Joseph McCarthy goes from figment of imagination to real-life incarnation each time you screw together a motor. You'll lavishly pay a premium for 4340 steel cranks, billet rods, and gas-ported pistons for their perceived superiority over lesser hardware, even if you don't know what the terms 4340, billet, and gas-ported really mean. On the other hand, like an insecure senator from Wisconsin, when presented with a large bill on stuff like align-boring, decking, and magnafluxing, you immediately suspect every shop of foul play because you don't know what align-boring, decking, and magnafluxing really mean. Strange, isn't it?
Granted, there's nothing wrong with seeking out the best value, but quality machine work costs good money. As your indentured servants in automotive journalism, we planned on spending an afternoon with the folks at the School of Automotive Machinists (SAM) in Houston, to have them explain the fundamentals of machining, but we ended up staying there three full days instead. Yes, much of that time involved SAM's instructors explaining the procedures in terms simple enough for magazine people to comprehend, but the point is that machine work requires much more skill, experience, patience, and time than many people realize-and that costs money.
Moreover, there's much more to gain from learning about machining than feeling better about spending your money. Along with the satisfaction that comes with knowing what certain procedures are, and how they're done, you'll be much better informed when deciding what items to order off your machinist's menu. Make no mistake, you're not going to be able to open up your own machine shop just by reading an article. However, you will know exactly how and why the most common procedures are performed.
BoringAs the miles tack onto a motor, cylinder walls wear out to a shape that's no longer perfectly cylindrical. Fortunately, just about every production block known to man is cast with additional meat that can be enlarged, or bored out, to "square up" the cylinders once again without compromising the block's integrity. As an added bonus, the motor picks up a few extra cubic inches in the process. The procedure isn't overly complicated, but still requires good equipment and a skilled set of hands. "A boring bar is only as good as its operator," says Pat Topolinski, an instructor at SAM. "Regardless of whether or not a block's set up straight in the fixture, it's going to bore a hole straight down."
In older machines that register off the deck surface, it's critical to check that the surface is completely flat before boring begins. Although there's nothing wrong with them, they do have a higher margin for error. The preferred method is with a boring machine that registers off the crankshaft centerline by attaching to the main bearing bores. This ensures that the cylinder bores will be perpendicular to the crank throws. Cylinders are typically bored to within a few thousandths of the final bore size and then honed to spec.
HoningWhile boring cleans up and straightens out cylinder walls by removing material, honing smoothes out the bores to provide a smooth surface for the pistons and rings to ride on. The final finish allows the rings to seal properly and also determines the amount of friction exerted on the reciprocating assembly. Generally, racers prefer a super-smooth finish to reduce ring drag in search for marginal gains in horsepower. However, this isn't necessarily the best approach for a street engine. Although a honed bore feels smooth to the touch, the finish is actually a series of fine peaks and valleys. Since the valleys retain the oil, smoother finishes reduce the depth of the valleys, and most engine wear occurs on cold starts. Street motors that will experience routine heat cycles need to sacrifice a bit of smoothness in the name of longevity. This is where your machinist's experience comes into play, as the grit of stones he uses will be determined by your motor's intended use.
Once considered exotic, but now thought of as common practice, is bolting a torque plate to the deck surface while honing. The process simulates the distortion a block experiences when a cylinder head is bolted into place, and is just another measure used to make sure the bores are as round as possible. Likewise, another procedure becoming more common and accepted for street motors is plateau honing, or honing in multiple stages. As the name suggests, an initial coarse honing stone is followed up by several finer grit stones in different stages to flatten the peaks in the finish. The result is deeper valleys that improve oil retention and lubrication for the pistons and rings, in addition to providing a smooth surface. "Almost all performance engines these days are plateau-honed," says Pat. "As far as the grit of the stones they're using, everyone has their own method, so it's somewhat secretive."
There is still some debate, however, regarding hot honing. It involves heating up the honing oil to roughly 200 degrees to simulate the expansion a block experiences at operating temperature. As with the use of torque plates, the idea is to get the bores as round as possible, but not everyone's convinced. "Some guys swear by it, but other guys try it once and never do it again."
DeckingTo promote proper cylinder-head sealing, the deck of the block is often surfaced, or decked, to provide a smooth, even surface for the gaskets and heads. As with boring, it is critical that the deck is machined perpendicularly to the crankshaft centerline. Since the pistons sit below the deck at top dead-center in most production blocks, the deck height is often reduced to improve quench and raise the static compression ratio.
BalancingBy nature, a 90-degree V-8 isn't the smoothest-running engine configuration, so balancing a performance rotating assembly requires some extra precision. As long as reciprocating mass is equal to the rotating mass, a motor will run smoothly without unwanted vibrations that reduce bearing life. With today's lightweight aftermarket pistons and rods, weight is removed from the counterweights the majority of the time. Only in applications where extremely heavy-duty nitrous or blower parts are used, or where the crank is extraordinarily light, is weight added to the counterweights.
In particularly high-rpm motors, the inertia generated by the reciprocating assembly increases at peak engine speeds, placing additional loads on the upper halves of the main bearings. Through thousands of hours of trial and error, engine builders and machinists have discovered that overbalancing a reciprocating assembly by adding 1 to 2 percent more weight to the counterweights will smooth out potential imbalances and even-out bearing wear. Doing so requires informing the machinist how high you plan on spinning the motor.
Align-Boring, Honing, And Four-Bolt MainsThe basic principles of align-boring and honing are similar to standard boring and honing, but for main caps instead of cylinder walls. The big difference is that, while over-boring a cylinder is a common rebuild procedure-since the crank rides on a set of bearings-only blocks that have been beat to death or have spun bearings require align boring. A much more likely reason for doing so is to install four-bolt main caps onto a two-bolt block. Like file-fitting a piston ring, to account for varying tolerances, aftermarket caps require some end-user trimming. Because they arrive undersized, they must be bored to the within a few thousandths of the proper inside diameter spec, then honed the rest of the way. Healthy blocks that aren't going to be fitted with aftermarket main caps typically only require align-honing.
Block PreparationIf simply freshening up a motor you know is otherwise in good shape or starting out with a brand-new block, you can immediately jump into the aforementioned machining operations. However, if you've rescued your block out of a junkyard, having it checked for cracks is imperative, unless you're not phased by the thought of spending thousands of dollars machining a piece of scrap.
Two inexpensive yet effective ways of ensuring a block is fissure-free are magnafluxing and pressure testing. Magnafluxing involves soaking the block in a luminescent solution that reveals cracks under florescent light. Likewise, sealing off the water jackets and pressure testing the coolant passages can find internal cracks and porosity issues not easily visible through magnafluxing.
Even if a block isn't cracked, sonic checking is a good idea, especially with blocks that have already been overbored. By sending sonic waves into the bores with a hand-held probe and reading how quickly they reflect back, sonic checkers can determine thickness at any given part of a cylinder wall. The most important areas to check are the major thrust surfaces, which is the inboard wall on the drivers side and the outboard wall on the passenger side.
After all that, once you've determined that the block is solid, giving it a thorough cleaning will not only make it easier to look at, but easier to work on as well. Hot tanking, the tried and true method, bathes or pressure washes the block in a high-alkaline caustic solution to dislodge grease and grime. Most the time it works reasonably well, but it doesn't completely clean water jackets, carbon deposits, rust, or scale in extremely well-worn blocks. In such instances, thermal cleaning is the hot ticket, where the block is baked to roughly 700 degrees to burn off all impurities. It is then media-blasted to remove all carbon, which also stress-relieves the block. Finally, the block is tumbled to remove all the metal shot, leaving behind a raw, cast-iron finish.