to bare metal without abrading the parent surface. Soda media is “softer” than other types of media and is “friable,” which means that the soda crystals break down upon impact (akin to throwing a snowball against a brick wall as opposed to throwing a rock against the same wall). Essentially, soda does the job without damaging the metal. Because soda is “softer,” and because it is water soluble, it leaves no abrasive grit that can damage moving parts (such as hood or door hinges).
Soda is nontoxic and nonhazardous, making its use far safer than other abrasive or chemical stripping methods. However, dry blasting generates a great deal of dust. For this reason, it is recommended that a dust mask be used, as well as eye and hearing protection.
In addition to blasting sheet metal material for body refinishing/restoration, soda is also an outstanding choice for blast-cleaning components such as frames, suspension parts, brake parts, engine components, etc. Because no hard abrasive grit is present, components such as engine blocks, cylinder heads, intake manifolds, etc., can be cleaned and then rinsed without concern for trapping damaging grit particles.
Aluminum Oxide
Depending on blast pressure, this can be very aggressive and leaves a coarse, textured finish. It’s economical, but be aware that it cuts very quickly and removes more metal. Used properly (level of blast pressure), you can avoid a too-rough finish.
Speed-Beed
This is a hybrid mix of 50- to 80-grit glass bead and 80-grit aluminum oxide. This provides faster cutting than glass bead but is not as aggressive as aluminum oxide.
Plastic Bead
Generally available in 30- to 40-grit size, plastic bead is good for removal of paint and surface rust. Plastic bead produces less blasting heat. This may be a good choice for cleaning gears, tooling, etc., because it doesn’t alter dimensions, and it doesn’t etch the surface.
A Special Note Regarding Intake Manifolds
Obviously, intake manifolds (single plane or dual plane) feature intake runners. Even after careful degreasing, blasting with an abrasive media can be dangerous, especially when dealing with a dual-plane intake manifold where you don’t have easy reach and access to all port surfaces. Fine media particles can embed into the material (or can be stuck in a remote piece of sludge or carbon), increasing the chance of that media eventually being sucked into the engine. If you do decide to blast an intake manifold with, for example, glass bead, you need to make absolutely certain that you eliminate any possibility of trapped particles inside the runners. If you feel the need to blast and you’re worried about leaving harmful particulates behind, soda is the best choice because it’s water soluble when rinsed. Even though the soda doesn’t pose a threat to the engine, any rust scale, dirt, etc., that’s held captive poses a serious risk. Regardless of the type of media you use, you still need to flush the runners surgically. If you do media-blast an intake manifold where you are uncertain about hidden debris, a follow-up cleaning in an ultrasonic unit along with a hot, soapy rinse/flush should remove any remaining contaminants.
Walnut Shell
Crushed walnut shell (aside from being biodegradable) is relatively gentle and is ideal for preserving surface micro finish while cleaning. Under controlled conditions, it’s also useful for those instances where you want to remove paint topcoats but retain the primer layer. Like most media, walnut shell is available in a variety of grit, from extra coarse to extra fine.
Corncob
Corncob is even softer, good for finalizing a nice satin finish. Either walnut shell or corncob can be very effective in removing paint and rust, without eating away at the base metal. And these organic types of media are relatively cheap.
A fine grade of walnut shell or corncob doesn’t remove any of the metal, it doesn’t etch or scratch softer metals, and the material doesn’t imbed into the metal surface. Walnut or corncob are great choices where a finer finish and retention of detail is important.
Steel Grit
A fine grade of steel grit leaves a relatively smooth finish. Steel cuts very fast and lasts longer (because it doesn’t 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
