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Aluminum Cleaning: A Small Shop’s Perspective
By David McLain
By David and Jerry McLain
Engine Builder magazine asked a specialist in rebuilding aluminum cylinder heads to detail his approach to cleaning. Many rebuilders today still struggle with cleaning aluminum properly, i.e., cleaned effectively with no damage to the head.
Chemical, aqueous and heat cleaning are all methods used by engine builders to clean aluminum. Those using all of these methods claim to be able to clean aluminum heads effectively. The following procedures used for cleaning aluminum heads are illustrative of a small machine shop/engine building operation that has obtained good results.
One Shop Owner’s Approach
Cleaning aluminum parts can be a really tough problem for small shops like ours (McLain’s Automotive Machine Shop and Dyno Service, Cuba, MO), as well as for large production engine rebuilders. On almost a daily basis our customers bring us aluminum heads and other aluminum parts that need machine work or welding. Those parts must be cleaned before any machine work can be done.
This article contains a brief overview of how my son David and I go about cleaning aluminum parts in our shop. Since aluminum heads make up about 95 percent of the aluminum parts we machine, this article will concentrate mostly on how our shop deals with them.
Before we get into the details of cleaning aluminum parts, lets talk about the type of aluminum we will be dealing with. There are several different aluminum alloys in common use in automotive engines. Each alloy has its own properties and characteristics. Different alloys machine differently and may react differently to various cleaning methods. Aluminum is soft and easily damaged with scrapers and abrasives. Aluminum oxidizes very quickly when exposed to air or certain chemicals. The aluminum oxide which forms on the surface of aluminum parts, actually protects the aluminum part from further oxidation.
Dave and I want the parts we repair and do machine work on to be clean when we return them to our customers. We make sure those parts are free of oil and grease, carbon, paint, old gaskets and anything else that may be clinging to the parts. We do not try to make the aluminum parts look like new! We do not bake our aluminum parts in an oven or heat them beyond those temperatures they would see in a running engine. Excess heat applied while cleaning changes the original heat treatment of the aluminum part and in addition may cause parts which rely on a press fit in the aluminum to relax, and loosen that press. Yes, our shop has a glass bead machine and we use it for many jobs that require glass beading. It does a great job, but we try not to use it to clean aluminum parts like cylinder heads or pistons. Glass beads are very hard and abrasive. When soft aluminum parts are blasted in a glass bead machine, we have found that some of those same beads that do such a great job of cleaning, get stuck in the metal. You can try to shake them out, blow them out, wash them out, or use any other method you may want to try to get rid of the beads, but some of those glass beads still seem to remain in the part. They get in bolt holes and spark plug threads, oil passages, and cooling system passages. But perhaps most importantly they can damage finely machined surfaces like cam bearing bores. So in most cases we do not throw anything at the aluminum part. No glass beads, steel shot, sand, or walnut shells.
We begin our cleaning process by soaking the part with a citrus-based cleaner like Zep 0455. The first step is designed to remove the oil and road dirt from the aluminum head. We use a parts brush to work the citrus cleaner into the dirt. We allow the part to soak for a few minutes and then it goes into the pressure washer. Here hot water and soap will remove nearly all the road dirt and oil.
The second step involves taking the head apart, separating the parts that can go into the hot tank from those that cannot. We now attack the carbon deposits in the combustion chambers and in the ports. The combustion chambers and ports are sprayed with a carbon dissolving cleaner like Zep Morado or another similar product. Please note these products can attack aluminum if you let it stand on a machined surface for more than a few minutes. Simply spray it on those areas that have carbon deposits, let it soak for a few minutes and, if necessary, use a small brush on the heavy deposits to help loosen them. Do not spray this cleaner into the cam bearing surfaces during the cleaning process. The part is now ready for another trip to the spray washer. The hot water and soap will now remove nearly all the carbon deposits. After drying, most aluminum parts are ready to move on to inspection, and to have the machine work begin.
There are always those exceptions that need extra cleaning. In these cases, where carbon deposits are extra thick or stubborn, we may use a soft wire brush and drill to break them up. Then we repeat the last step. In a few cases we will put the part in the cold parts cleaner and allow it to soak an hour or so. Since all the oil and grease has been removed before the part gets to this point, your cold parts cleaner will last a long time. Pressure wash the parts to remove any traces of the cold parts cleaner and remaining carbon.
We clean all manifold surfaces with a sharp gasket scraper pulling it backward to avoid digging into the soft aluminum. A small electric sander with an 80-grit paper is then used to finish clean the manifold surfaces. A small 3M Scotch Brite disk is sometimes used to clean around the studs on the manifold surface. Great care must be used when cleaning any aluminum surface with a power tool. You can do lots of damage to the part you are trying to clean, by rounding off edges or causing low spots on the sealing surface.
The head is now ready to move into the machining area where guides, seats and valves are reconditioned. Finally the head is resurfaced to the proper surface finish, as recommended by our gasket supplier. The head is again washed with hot water and air-dried. We want to make sure any grit or chips left over from the machining process are removed before the head is assembled.
As you can see we rely on soap and hot water under high-pressure to do a lot of our cleaning. We use chemicals to break down the oil and carbon during the cleaning process. The oil is safely removed by the skimmer on our spray washer and disposed of properly. Our cleaning process requires several trips to the pressure washer and some manual cleaning, but we feel the finished product is worth the extra effort. When our customer reinstalls the reconditioned cylinder head on his customer’s vehicle he knows the head has been properly machined and cleaned and is in excellent condition.
Editor’s note: Obviously there are many different approaches to cleaning and machining engine blocks, heads, and other components. What is an efficient and effective method for a smaller two-man shop might not even be an appropriate consideration for a larger operation demanding quick turnaround times.
From time to time Engine Builder magazine will provide a specific shop’s approach to engine building. We welcome your perspective. Call us at 330-670-1234.