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Cleaning engine blocks and cylinder heads is just as important as the machining operations you will perform on the castings. You can’t do a thorough job of inspecting these parts if they are dirty, greasy or covered with paint or corrosion. Checking for cracks in cast iron heads and blocks requires a clean surface for the magnetic particle detection powder. Likewise, checking aluminum castings for hairline cracks with penetrating dye also requires a clean surface. Even porosity leaks in aluminum heads and blocks may be masked if there’s a heavy layer of gunk on the metal.
You also don’t want to gum up your shop equipment while you’re machining the castings, and you don’t want any surface contaminants interfering with precision machine work such as honing or resurfacing. Most late-model heads require a mirror-like finish to seal the MLS gaskets, so any debris that’s snagged and drug across the metal by the milling head may mar the mating surface. Clean bare metal is all you want to see following the initial cleaning process.
There’s no single cleaning process that is right for every application because aluminum and cast iron are very different metals. Aluminum is much softer than cast iron and much more sensitive to high temperatures (anything over 450° to 500° F.). Too much heat can anneal and soften the metal. Aluminum is also porous and more chemically reactive than cast iron. Harsh cleaning solutions that work well on cast iron may discolor and tarnish aluminum’s naturally bright finish.
Clean bare aluminum quickly forms a surface layer of aluminum oxide that stops further oxidation, and the color is the same as the base metal so there is no change in appearance or color. Most customers want a bright, like-new finish on their aluminum heads and blocks so it’s important you use a cleaning process that can do just that. Of course, the other option is to camouflage a discolored casting with aluminum paint before it goes out the door.
Cast iron, by comparison, can withstand just about any cleaning process you can throw at it: harsh caustic chemical solutions, acid dips, lots of heat (indirect heat or open flame) and almost any kind of abrasive blast media. But as tough as cast iron is, its Achilles’ heel is rust. Iron has a strong affinity for oxygen and wants to revert back to its natural state (iron oxide) as soon as clean bare metal is exposed to air – especially if there’s moisture or humidity to accelerate the process.
Because of this, rust control and prevention are major concerns when cleaning and preserving cast iron blocks and heads. The cleaning process you choose to use on cast iron should therefore include some type of rust inhibitor or post treatment to prevent the metal from turning an ugly brownish red. The castings will eventually be painted or powder coated, but it’s important to keep rust formation to a minimum until the assembled parts are either returned to the customer or are ready to paint.

Making Dirty Parts Clean

After tens of thousands of miles of everyday driving, even the cleanest engine is covered with crud. Oil leaks and dirt combine to form a greasy coating on the outside of the engine. The factory paint can chip and peel away as a result of heat and surface corrosion, allowing exposed iron to rust. Aluminum heads and blocks can become dull and discolored. Road salt can etch and corrode aluminum, and form a rusty crumbly mess on exposed cast iron surfaces.
Internally, engines get dirty too, with hard carbon deposits coating the combustion chambers and exhaust ports. Scale and lime deposits can form a thermal barrier inside the cooling jackets around the cylinders and combustion chambers. Oil varnish deposits and sludge can build up in oil galleys, valleys and other internal block and head surfaces that are bathed with oil.
All of these external and internal surface contaminants have to be removed by the cleaning process you choose, not only to allow inspection and relatively clean machining but to also eliminate contaminants that could cause trouble if not removed. Machined parts also require some type of post-cleaning to remove oils, metal chips and honing residue.
Never assume a customer will do a good job of cleaning their block and heads after you’ve done the required machine work. They might or they might not, but if there are any problems they will likely blame you when contaminants chew up the bearings, score the crank or cam journals, scuff the cylinders and pistons or cause the engine to fail. Think of post-cleaning as added insurance against comebacks.
Post-cleaning after machining should remove all traces of metal chips and honing residue as well as any blast media or shot reside that may be lurking in nooks and crannies of the heads and block. The final cleaning process should leave the metal with a bright, clean, cosmetically-appealing  finish – unless, of course, you are painting the castings. Even then, you need an oil-free clean surface for the paint to stick.

Choosing A Cleaning Process

Obviously, the process you choose to clean blocks and heads must be effective at removing dirt, grease, oil, paint, carbon, rust and scale from internal as well as external surfaces. The process should also require the least amount of time, labor and energy to complete because cleaning costs can often account for as much as 20 to 30 percent of the cost of rebuilding some engines.
The less manual labor it takes to clean the parts, the better. Besides, cleaning is a dirty job that nobody loves doing so the more automation you can incorporate into the process, the more your employees will appreciate it. The best cleaning methods only require you to load the parts and turn on the equipment. So whether it’s load and spray, soak and penetrate, cook and vaporize, or blast and rinse, the more work the cleaning equipment can do for you, the less handling, scrubbing and scraping you’ll have to do to get the parts clean.
There are lots of ways to clean blocks and heads and different shops use different cleaning techniques for different reasons. If you’re building performance engines and working primarily with new castings, you shouldn’t have to deal with much dirt and grease and grime. Post-machining cleaning to remove cutting oils, metal chips and honing residue is probably all you’ll have to worry about. On the other hand, if you’re rebuilding old, dirty, greasy, high-mileage engines that look like they’ve been dragged through the mud behind a 4X4 or used as a boat anchor for the past 30 years, cleaning can be more of a challenge.
Cost is another variable that affects the type of cleaning process you may choose to use. If you can’t afford the equipment, it’s not an option. Spray cabinets and thermal ovens and flame rotisseries and ultrasonic tanks and blast cabinets are great to own, but if all you can afford is a discount store power washer and a small solvent tank, your cleaning capabilities will be greatly limited.
Spray aerosols such as gasket remover, engine degreaser, brake cleaner or general purpose cleaners can all be used to clean heads and blocks, but they also take a lot of scrubbing and hand washing to get the parts clean. That’s why you need to think about upgrading your cleaning capabilities if you are still cleaning parts the old fashioned – and often environmentally-unfriendly – way.
Space limitations within your shop may also limit your ability to use the type of cleaning equipment you’d like to use. If this is the case, you may be able to farm out some of your more challenging cleaning needs to another shop.
You may also encounter environmental restrictions on the type of cleaning processes and chemicals you can use. Some jurisdictions may limit stack emissions from thermal cleaning systems or the use of high VOC (Volatile Organic Compound) chemicals. There may also be restrictions on what you can pour down the drain or send to a local landfill. Hazardous waste disposal costs can really add up, so the less waste you produce, the less cost you’ll have to bear in getting rid of it.
You also have to consider the cost of the cleaning equipment, the cost to maintain that equipment (maintenance contracts and repairs), the cost to operate the equipment (energy costs and energy efficiency), and the cost to get rid of any residues or hazardous waste generated by the cleaning process. Your equipment supplier can fill you in on the details here. Just make sure you ask all the right questions and get them answered to your satisfaction!

 

Which Cleaning Process Works Best?

It depends entirely on the application. The first and foremost consideration should be the effectiveness of the cleaning process. Does it remove all of the contaminants and get the heads and block reasonably clean? In some instances, it may take more than one type of cleaning process to achieve the state of cleanliness you desire. A process that does a great job removing dirt, grease and oil may not do as well removing rust or carbon.
Some cleaning processes that work extremely well on the exterior surfaces of castings (such as spray washing) don’t do much of anything to clean the insides of the casting such as the cooling jackets and oil galleys. So you have to pick and choose the process or combination of processes that will do everything you want to accomplish.
Spray washers are great for washing off external surfaces as well as any exposed internal surfaces the jet stream can reach. Spray washers require the right type of detergent for the metal being cleaned, and are most effective when the water temperature is maintained within the specified working range of the cleaner (which may range from room temperature up to 170° F or more). Hotter usually cleans better, but hotter also increases your energy costs.
Hot tanks (filled with caustic or some type of aqueous cleaner) are good at cleaning both the inside and outside surfaces of castings. Submerging the parts and allowing them to soak for an extended period of time will loosen most of the stuff you don’t want on the metal. As with spray washers, heat usually accelerates the cleaning process as does agitation. The concentration of the cleaning solution in the tank also has to be maintained and replenished as needed to keep the tank operating at peak efficiency. The gunk that settles to the bottom also has to be cleaned out periodically.
Choosing the right chemicals or detergents is absolutely essential for effective cleaning. A highly caustic

solution in a hot tank or spray washer can do an excellent job of cleaning cast iron heads and blocks, but it may discolor or etch aluminum. Conversely, a cleaning agent or detergent that is formulated for aluminum may not be the best choice for cleaning cast iron. Some cleaning products are “general purpose” cleaners that can be used on both cast iron and aluminum, but there may be tradeoffs such as longer process times to clean cast iron or some metal discoloration when cleaning aluminum.
An ultrasonic tank can do magic on all kinds of parts. The ultrasonic sound waves literally blast dirt and grime off both external and internal surfaces with tiny imploding bubbles. Ultrasonic cleaning can also reach into blind holes and deep recesses to blast the surface clean.
If you’ve never seen ultrasonics in action, you will be amazed at how grease and oil just melts off the surface – and it’s extremely fast provided the parts are not caked with a heavy thick coating of dirt and grease. Ultrasonics is often used as a secondary fine cleaning process after parts have been spray washed or baked. The frequency and power level of the ultrasonics can be tuned to the type of parts being cleaned, giving you even more leverage in your battle against grime.
Thermal cleaning in a oven or an open flame rotisserie can burn off gunk both inside and outside blocks and heads. An open flame is especially good at burning off high temperature oils such as synthetics. But thermal cleaning always requires a subsequent cleaning process (shot blast, glass bead, soda blast or spray washing) to remove the ash residue. Too much heat can anneal and soften aluminum castings, so the heat has to be turned down when cleaning aluminum heads or blocks. You should never attempt to clean cast iron and aluminum parts in the same batch.
High temperatures inside a cleaning oven can also loosen the seats and valve guides in aluminum heads. If the seats and guides are being replaced anyway, it’s no big deal and may save you some disassembly time. On the other hand, if the original seats and guides are being reused, and you don’t want them to fall out, thermal cleaning may not be the best option for

aluminum heads.
The cleaning technique (or combination of methods) you use should leave the heads and block free of dirt, grease, carbon and lime deposits. Residual carbon deposits that are still clinging to combustion chambers or exhaust ports can be brushed or blasted away, but that requires additional manual labor (which should be avoided to minimize your cleaning costs).
The cosmetic appearance of the metal doesn’t matter until the final post-machining cleaning has been completed and the block and heads are ready to be assembled, painted and/or bagged and returned to the customer. Bagging is highly recommended to keep out dirt while parts are being stored and transported.
When final cleaning an engine block, the cylinders should be manually scrubbed with hot soapy water to remove all traces of honing residue from the bore surfaces. Wiping the cylinders with ATF or WD-40 can prevent rust but it won’t remove honing residue. You have to use detergent to loosen, lift and wash away the residue.
Dry blasting aluminum with glass beads, aluminum oxide grit or steel shot (stainless works well and lasts a long time but is expensive) can remove discoloration. But this requires an additional cleaning step to make sure no beads, grit or shot are left behind in any of the nooks and crannies of the casting. Masking off the valve guide and cooling jacket openings prior to bead or grit blasting can reduce the risk of media being retained.
Another cleaning alternative is to use a soft blast media such as plastic beads, walnut shells or baking soda to clean both cast iron and aluminum castings. Baking soda has proved to be an effective cleaning media on cast iron and aluminum, and can be used dry or mixed with water to create a cleaning slurry. Adding some aluminum oxide to the mixture can increase its cutting action even more.
Baking soda is relatively soft compared to other traditional blast media (only 2.5 on the Mohs hardness scale), and it is inexpensive and is water soluble (making it easy to wash off afterwards). It can scour away carbon, rust and paint, but unlike other media dry soda can only be used once (wet soda can make several passes).
When baking soda hits the surface of the metal, it fractures as it knocks loose the surface contaminants. This creates a lot of dust, so the blasting has to be done in a sealed cabinet. By comparison, wet soda blasting is a closed-loop process that eliminates the dust.

The process you choose to clean blocks and heads must be effective at removing dirt, grease, oil, paint, carbon, rust and scale from internal as well as external surfaces. This head was half cleaned with an ultrasonic system.

 

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Larry Carley

Larry Carley

Larry Carley

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