Automotive Machining. Mike Mavrigian
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 like to preheat some parts to cook off any residual oils, prior to glass bead blasting.
This block has been degreased, but surface rust and some contaminants remain.
The same block has now been shot blasted and tumbled. The block is now ready for machining.
There are instances where washing/scrubbing and rinsing by hand are applicable, such as performing a final wash and rinse of an already-machined engine block prior to assembly. Using very hot water (as hot as your hands can tolerate) and Dawn dishwashing liquid can produce excellent results. With the block on a stand that allows you to rotate the block, shoot hot water into all oil and coolant passages, and then pour Dawn into the same passages. Using dedicated (and clean) bristle brushes that are designed for block cleaning, scrub passages as access permits; follow with multiple hot water rinses until all traces of soap are eliminated.
This Chevy big-block has been stripped down and placed into a cleaning oven. The block is secured within a tubular cage. With the cage mounted in the oven, the machine rotates the block during the thermal cleaning process to distribute heat evenly, cooking off all grease, paint, rust, and sludge.
Here, the airless shot blasting process has been completed, resulting in a clean, down-to-bare-metal block that’s ready for tumbling. After the block has cooled down in the oven, the block, still mounted in its cage, is moved to an airless steel shot blasting cabinet, which cleans off the ash created by the oven.
An enclosed blast cabinet can be ideal for cleaning certain parts, such as pistons, connecting rods, mounting brackets, valvecovers, etc., but the media must be selected carefully. A variety of blasting media is available, including but not limited to “glass bead,” crushed walnut shells, crushed corncobs, crushed pecan shells, plastic bead, and soda. Depending on the media, you can accomplish not only cleaning to bare metal, but also lightly deburring razor-sharp edges where desired. Never use a high-abrasive media such as sand, which is simply far too aggressive. If an abrasive media is used, such as glass bead, the component must be thoroughly and carefully washed and rinsed afterward to remove all bead particles. For that reason, it is not wise to glass bead blast an item such as an intake manifold, because the possibility of particles being trapped inside runners is too great.
The cage is then disassembled and removed from the block. Using the shop’s overhead crane, the caged block is removed from the shot blaster.