Automotive Machining. Mike Mavrigian
fracture, as opposed to aluminum oxide). However, steel grit will likely create more wear and tear on your blasting equipment (nozzle, pickup tube, power head, hose, etc.). It is not for delicate parts or surfaces.
Silicon Carbide
This media stays sharper and lasts longer than other types, but is aggressive and creates even faster wear of blasting equipment.
Tumbling and Vibratory Cleaning
This method involves “tumbling” immersed parts in a soup of dry or wet media, where tumbling or vibration treats the parts. The media can be steel, ceramic, or other material that is available in a wide variety of shapes and sizes. The type of media depends on the desired results, which can include cleaning, deburring, or polishing. Tumblers come in a range of sizes, from small to industrial-large. The parts are randomly rotated in the media mix, with contact among the media particles stripping the parts down to bare metal. Small tumblers are excellent choices for cleaning small items such as valves, valvesprings, retainers, rockers, etc. Unlike blast cleaning, there’s no particle or dust cleanup required and no nasty solvents to deal with. To protect valvestems, a piece of runner tubing can be slipped over the valvestem.
Vibratory tumblers may use either a dry or wet slurry of stones. A wet slurry is commonly used for polishing as opposed to cleaning.
An ultrasonic cleaning system is another option for cleaning delicate parts where you want to avoid abrasives or strong chemicals. The parts are placed into a water tank, and frequencies are induced into the water to essentially vibrate particles loose. For example, this type of cleaning system is popular among shops that restore high-pressure fuel injectors for diesel engines.
Cleaning with Hand and Power Tools
In certain instances, surfaces may be cleaned of heavy buildup of paint, sludge, or carbon deposits if you don’t have access to the proper shop equipment. A handheld pneumatic scaler or scraper may be used to remove heavy sludge from a block exterior. A handheld scraper or pneumatic scraper may be used to remove stubborn gasket material. A flared/flat-face wire brush may be used on a drill or pneumatic die grinder on a block exterior, on cylinder head combustion chambers. Again, this is only to remove heavy deposits.
A Roloc bristle pad powered by a drill or die grinder may also be used for these same purposes. However, never attempt to clean or prepare any critical surfaces by hand, such as cylinder head or block decks, intake manifold decks, etc. You can easily damage the surfaces by creating waviness on the decks, which then requires resurfacing to regain proper flatness. You simply cannot obtain a flat surface, because you cannot control your hand and tool pressure adequately enough. Also, do not attempt to hone cylinder bores or lifter bores with the use of a handheld tool. You aren’t able to achieve a precise diameter or cylindrical uniformity.
By the way, Scotch-Brite pads, although wonderful for scuffing or cleaning some metal surfaces, have no place in an engine preparation room. The tiny fibers left over from use can easily contaminate not only the engine that you’re working on, but any other engines or equipment in the same room. Whether or not you use Scotch-Brite pads during initial cleaning, never have them anywhere near the engine during assembly.
A Roloc bristle head operated with a pneumatic die grinder can be used to remove deposits from various external surfaces.
Precision measurement tools are a necessity for both machining and assembly procedures. In this chapter I discuss common precision measurement tools and systems that are used on a routine basis in any engine machining shop.
A micrometer is a measurement tool available in various formats, including an outside micrometer, used to measure thickness, length, or diameter; an inside micrometer, used to measure inside diameter of a hole; and depth micrometers, used to measure hole depth.
An outside micrometer features a C-clamp style frame. At the far end is a flat-faced anvil. Facing the anvil at the opposite end of the frame is a flat-faced spindle. The anvil is in a fixed position on the frame. The spindle moves as the micrometer is adjusted. The sleeve features incremented index marks and is stationary. The thimble at the far end of the grip rotates and features additional marks. A lock lever is provided to secure the adjustment in a locked position when required.
An inch-format micrometer features an internal screw drive that features 40 threads per inch. One complete revolution of the screw moves the thread 1/40, which is equal to .025 inch. Each mark on the sleeve represents .025 inch. The beveled face of the thimble has 25 equally spaced lines that each represents .001 inch.
The primary components of an outside micrometer are labeled here, including the frame, stationary anvil, sliding spindle, stationary index marked sleeve, and rotating thimble. Micrometers feature a lock that allows you to lock a measurement for reference. This micrometer features a toggle lever lock. A micrometer set typically includes ranges of 0 to 1 inch, 1 to 2 inches, 2 to 3 inches, and 3 to 4 inches. Also included are three calibration standards and a spanner wrench for adjusting micrometer calibration.
When reading a micrometer, first note the larger lines and numbers on the sleeve, and then look at the smaller lines between the numbered lines. As an example, if the number 3 is visible on the sleeve, that means that you are measuring at least .300 inch. Let’s say that three smaller lines after the number 3 are also visible. You now know that the measurement is at least .375 inch (remember that each line indicates .025 inch, so seeing three of these lines indicates .075 inch).
Next, note the lines on the moving thimble to see which thimble line matches up to the last visible line on the sleeve. As an example, let’s say that the thimble line is identified as number 8. Because each thimble line indicates a space of .001 inch, that means that you have an additional .008 inch. Because the previously noted measurement was .375 inch, when you add the spindle sleeve mark of 8, the final measurement is .383 inch.
This sample reading shows the number-2 line flush with the chamfered edge of the thimble, with the zero line of the thimble aligned with the horizontal sleeve line, indicating exactly .200 inch.
A first-time user of a micrometer will likely be intimidated, but with a bit of practice, reading a micrometer becomes much easier.
When measuring a part with a micrometer, adhere to one rule: go slowly. Avoid spinning or twirling the thimble. Work slowly and carefully. Adjust the micrometer to almost the desired opening by rolling the thimble along your hand; avoid twirling it. Place the micrometer onto the part, holding it firmly with one hand. Use your sense of feel to make sure that the axis of the micrometer is perpendicular to the measured surface. Don’t rock the micrometer; use your sense of feel. Close the micrometer using the ratchet knob to close the micrometer until the spindle is almost touching the part. Then gently