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.

Boring is performed on machines like this Rottler FA unit, which registers off the mains to ensure cuts are made perpendicular to the crank centerline. The most critical step in the procedure is centering the boring bar, which is accomplished by equalizing the gap between three fingers (space 120 degrees apart) that extend from the bar with a feeler gauge.

A very precise indexing tool is used to set the depth of the cutter. Twisting the knob on the left for the desired amount of overbore locates the cutter in the proper position within its housing, which then inserts into the boring bar.

The rate at which the boring bar cuts depends on how much metal is being removed at one time. With a larger overbore, the bar descends slower than with smaller overbores, and vice–versa. Boring a block 0.030–over typically requires 40 minutes.

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.

Boring

As 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.

Honing

While 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.

There are newer machines out there, but the industry stalwart for honing is the Sunnen CK-10. The first step in honing is shimming the stones for the final bore size that will be achieved. For the ultimate in precicsion, a head gasket close in thickness to the one that will be run on the motor is sandwiched beneath the torque plate.