to test fitting and/or final engine assembly, cleanliness is absolutely critical. This includes every component involved (block, crankshaft, connecting rods, pistons, camshaft, timing system, oil pump and pickup, oil pan, valvecovers, intake manifold, cylinder heads, rockers, pushrods, lifters, timing cover, etc.). There is no such thing as “too clean.”
A variety of cleaning methods are available, depending on the application. These include hot tanks, spray cabinets, ovens, airless shot blasting, cabinet media blasting, tumbling, and manual cleaning involving hand or power tools.
An airless shot blaster slings steel (or stainless steel) shot onto the block or cylinder heads as the part is rotated while secured in an adjustable cage. Compressed air is not used. Following shot blasting, the part must be tumbled in a rubber-lined drum to shake any remaining steel shot from the part.
An airless shot blaster cabinet uses a high-speed impeller that blasts steel shot at the parts as the parts slowly rotate in a cage. This machine does not use compressed air. The steel (or stainless steel) shot is about .030 inch in diameter. After the part has been blasted, the part must then be tumbled in a large tumbling drum to remove any remaining shot. Airless blasting with steel shot is intended for cast-iron parts only and should not be used on softer aluminum parts. Components may only be airless shot blasted after they have been degreased and are thoroughly dry.
Solvents heated at approximately 170 degrees F break down contaminants faster than room-temperature solvents. However, solvents must be chosen carefully to be compatible with ferrous (steel or iron) or nonferrous (alloys) components. After a part has been cleaned in a hot tank, it must be rinsed in hot water and then blow-dried. At this point, steel or cast-iron surfaces tend to surface rust very quickly, so application of a rust inhibitor is required as soon as possible. Hot tanks are available in various types, including hot-soak and hot-soak with agitation and spray jets.
A “jet” spray machine uses heated solvent and a series of high-pressure spray nozzles. The parts being cleaned are secured in a cage or appropriate mount, on a turntable. The part is rotated during the wash and rinse cycle. Liquids, depending on the application, can include hot water and/or solvents appropriate for the material being cleaned. High-caustic solvents may be appropriate for steel or cast-iron; a detergent-based cleaner is best for aluminum parts.
Threaded Holes
Regardless of the cleaning method, all threaded holes in the engine block should be inspected and cleaned. Be sure to clean all threaded bolt holes and give special attention to the cylinder head deck and main cap threaded holes. Using a rifle-style bristle brush, scrub all female threaded holes. To make sure that threads are in good condition, and to remove any contaminants/debris, it’s a good idea to run a chasing tap through all threaded holes.
Do not confuse this with a cutting tap. Common cutting taps tend to remove metal, which is to be avoided. Chasing taps are specially designed to both clean and re-form existing threads without removing excess material. Especially for main cap bolt holes and the block’s cylinder head deck bolt holes, using a chasing tap helps to ensure that the threads are clean while retaining the necessary strength and integrity.
Scrub the block exterior with a clean, soft brush soaked in hot water and Dawn and rinse. I’m not trying to promote the brand of detergent, but for some reason, Dawn seems to do the best job of removing oils and grease. When all internal and exterior surfaces have been thoroughly rinsed, blow clean compressed air through all bolt holes, passages, and exterior surfaces. At this point, when the block is dry, immediately apply a thin coating of clean engine oil to main saddles, lifter bores, and cylinder bores to prevent surface rusting. Cast-iron blocks tend to oxidize (surface rust) very quickly when clean and dry, so this is a good time to mask and paint the block exterior. If the part is not to be painted, apply a thin coat of a rust inhibitor to all surfaces, especially if the part is stored for a while prior to assembly.
All threaded holes in a block should be chased to ensure cleanliness and thread condition. Here, a block’s cylinder head deck hole is being chased. Drive the tap with a hand driver only. A variety of sizes is needed to cover all holes. The most critical threaded holes include the block’s head deck holes and the main cap holes.
Commonly available parts washers that use a cold (unheated) solvent are useful for degreasing smaller parts such as connecting rods, pistons, camshafts, etc., but this requires allowing the parts to soak and then be hand-brushed or scraped to remove grease and other solvent-soluble contaminants. However, since no pressure is involved, this may or may not remove contaminants from blind holes or passages. Also, this process is time-consuming and is not generally used in an engine builder’s shop.
A hot jet spray wash is commonly used to clean blocks, cylinder heads, crankshafts, and more. The table rotates as high-pressure heated solvent or detergent is sprayed.
This block has been oven cleaned, tumbled, and washed in a jet spray cabinet to a like-new finish.
Often referred to as thermal cleaning, a dedicated oven can be used to degrease an engine block or cylinder heads. A dedicated cleaning oven “cooks” the component, turning grease, oils, paint, and other contaminants to ash. The component is initially heated to about 375 degrees F to cook off surface vapors, which are then oxidized in a separate chamber at about 1,300 degrees F. The oven’s primary chamber then rises to a higher preselected temperature of about 600 to 700 degrees F, for steel or cast-iron components. When the cleaning cycle is complete, which usually takes about three hours or so, all sludge contaminants have been reduced to easily disposable ash. After the component has cooled, it is then washed/rinsed in a hot tank to remove remaining particles.
Aluminum components require more care because extreme temperatures can result in distortion. Typically, aluminum castings cook at about 500 degrees F. This lower temperature also reduces the chance of valveseats and guides loosening in cylinder heads. Regardless of material (steel, iron, or aluminum), the oven temperature must drop very slowly after the cooking stage until reaching room temperature, to prevent metal distortion.
Although a hot tank accumulates sludge and requires periodic cleaning and proper disposal, the use of a cleaning oven eliminates the need to dispose of hazardous waste (sludge), making ovens a bit more environmentally acceptable.
Although most cleaning ovens are designed to rotate the part during the heat cycles to evenly heat the part, some engine builders
