Cleaning Engine Parts

After the component that needs service has been disassembled, its parts should be thoroughly cleaned. The cleaning method depends on the component and the type of equipment available. An incorrect cleaning method or agent can often be more harmful than no cleaning at all. For example, using caustic soda to clean aluminum parts will dissolve the part. Caustic soda is a strong detergent that is commonly found in solvents that are effective in removing carbon.

!WARNING! Always wear the appropriate eye protection and gloves when working with cleaning solvents.

Only after all components have been thoroughly and properly cleaned can an effective inspection be made or proper machining be done.

Types of Contaminants:

Being able to recognize the type of dirt you are to clean will save you time and effort. Basically there are four types of dirt.

Water-Soluble Soils--The easiest dirt to clean is water-soluble soils, which includes dirt, dust, and mud.

Organic Soils--Organic soils contain carbon and can not be effectively removed with plain water. There are three distinct groupings of organic soils:

¦ Petroleum by-products derived from crude oil, including tar, road oil, engine oil, gasoline, diesel fuel, grease, and engine oil additives

¦ By-products of combustion, including carbon, varnish, gum, and sludge

¦ Coatings, including such items as rust-proofing materials, gasket sealers and cements, paints, waxes, and sound-deadener coatings

Rust--Rust is the result of a chemical reaction that takes place when iron and steel are exposed to oxygen and moisture. Corrosion, like rust, results from a similar chemical reaction between oxygen and metal containing aluminum. If left unchecked, both rust and corrosion can physically destroy metal parts quite rapidly. In addition to metal destruction, rust also acts to insulate and prevent proper heat transfer inside the cooling system.

Scale--When water containing mineral and deposits is heated, suspended minerals and impurities tend to dissolve, settle out, and attach to the surrounding hot metal surfaces. This buildup of minerals and deposits inside the cooling system is known as scale.

Over a period of time, scale can accumulate to the extent that passages become blocked, cooling efficiency is compromised, and metal parts start to deteriorate.

Cleaning with Chemicals:

There are three basic processes for cleaning automotive engine parts. The first process that is discussed is chemical cleaning.

This method of cleaning uses chemical action to remove dirt, grease, scale, paint, and/or rust.

CAUTION! When working with any type of cleaning solvent or chemical, be sure to wear protective gloves and goggles and work in a well-ventilated area.

Prolonged immersion of the hands in a solvent can cause a burning sensation. In some cases a skin rash might develop. There is one caution to mention about all manufactured cleaning materials that cannot be overemphasized: Read the labels carefully before mixing or using.

Unfortunately, the most traditional line of defense against soils involves the use of cleaning chemicals.

Chlorinated hydrocarbons and mineral spirits may have some health risks associated with their use through skin exposure and inhalation of vapors.

Hydrocarbon cleaning solvents are also flammable.

The use of water-based nontoxic chemicals can eliminate such risks.

!WARNING! Prior to using any chemical, read through all of the information given on the material safety data sheet (MSDS) or the Canadian workplace hazardous materials information systems sheets (WHMIS) for that chemical. Become aware of the health hazards presented by the various chemicals.

Hydrocarbon solvents are labeled hazardous or toxic and require special handling and disposal procedures. Many water-based cleaning solutions are biodegradable. Once the cleaning solution has become contaminated with grease and grime, it too becomes a hazardous or toxic waste that can be subject to the same disposal rules as a hydrocarbon solvent.

Some manufacturers offer waste-handling and solvent recycling services. The old solvent is recycled by a distillation process to separate the sludge and contaminants. The solvent is then returned to service and the contaminants disposed of. Independent services for maintaining hot tanks and spray washers are also available.

CAUTION! Care needs to be taken with alloy blocks with sleeves or liners. The different metals react differently to chemicals. Make sure to check with the service manual before using a cleaning solution on these parts. The wrong chemical can cause damage to the block and/or sleeves.

Chemical Cleaning Machines

Parts Washers--Parts washers (often called solvent tanks) are one of the most widely used and inexpensive methods of removing grease, oil, and dirt from the metal surfaces of a seemingly infinite variety of automotive components and engine parts. A typical washer setup might consist of a tank to hold a given volume of solvent cleaner and some method of applying the solvent. These methods include soaking, soaking and agitation, solvent streams, and spray gun applicators.

+++0-25 A typical parts washer.

+++0-27 A hot spray cleaning machine.

+++0-26 A hot soak (d.p) tank.

Soak Tanks--There are two types of soak tanks: cold and hot. Cold soak tanks are commonly used to clean carburetors, throttle bodies, and aluminum parts. A typical cold soak unit consists of a tank to hold the cleaner and a basket to hold the parts to be cleaned.

After soaking with or without gentle agitation is complete, the parts are removed, flushed with water, and blown dry with compressed air.

Cleaning time is short, about 20 to 30 minutes, when the chemical cleaner is new. The time becomes progressively longer as the chemical ages. Agitation by raising and lowering the basket (usually done mechanically) will reduce the soak period to about 10 minutes. Some more elaborate tanks are agitated automatically.

Hot soak tanks are actually heated cold tanks. The source of heat is electricity, natural gas, or propane.

The solution inside the hot tanks usually ranges from 160°F to 200°F (71°C to 93°C). Most tanks are generally large enough to hold an entire engine block and its related parts.

Hot tanks use a simple immersion process that relies on a heated chemical to lift the grease and grime off the surface. Liquid or parts agitation may also be used to speed up the job. Agitation helps shake the grime loose and also helps the liquid penetrate blind passageways and crevices in the part. Generally speaking, it takes one to several hours to soak most parts clean.

Hot Spray Tanks The hot spray tank works like a large automatic dishwasher and removes organic and rust soils from a variety of automotive parts. As with the hot soak method, spray washers soak the parts, but they also have the benefit of moderate pressure cleaning.

Using a hot jet spray washer can cut cleaning time to less than 10 minutes. Normally, a strong soap solution is used as the cleaning agent. The speed of this system, along with lower operating costs, makes it popular with many machine shop owners.

SHOP TIPS--Caustic soda, also known as sodium hydroxide, can be a very dangerous irritant to the eyes, skin, and mucous membranes. These chemicals should be used and handled with care. Because of the accumulation of heavy metals, it’s considered a hazardous waste material and must be disposed of in accordance with EPA guidelines.

Spray washers are often used to preclean engine parts prior to disassembly. A pass-through spray washer is fully automatic once the parts have been loaded, and the cabinet prevents the runoff from going down the drain or onto the ground (which is not permitted in many areas because of local waste disposal regulations). Spray washers are also useful for post-machining cleanup to remove machine oils and metal chips.

+++0-28 A cleaning furnace.

+++0-29 Using a power scraper pad will prevent any metal from being removed.

Thermal Cleaning:

The second basic process for cleaning engine parts is thermal cleaning. This process relies on heat to bake off or oxidize dirt and other contaminants.

Thermal cleaning ovens ( +++0-28), especially the pyrolytic type, have become increasingly popular.

The main advantage of thermal cleaning is a total reduction of all oils and grease on and in blocks, heads, and other parts. The high temperature inside the oven (generally 650°F to 800°F [343°C to 426°C]) oxidizes all the grease and oil, leaving behind a dry, powdery ash on the parts. The ash must then be removed by shot blasting or washing. The parts come out dry, which makes subsequent cleanup with shot blast or glass beads easier because the shot won’t stick.

SHOP TIPS--A slow cooling rate is recommended to prevent distortion that could be caused by unequal cooling rates within complex castings.

+++0-30 Carbon can be removed with a wire wheel driven by an electric or air drill motor.

+++0-31 It’s often necessary to remove the gallery plugs and hand clean the oil galleries.

+++0-32 Using a blast nozzle to clean the backside of a valve.

One of the major attractions of cleaning ovens is that they offer a more environmentally acceptable process than chemical cleaning. But although there is no solvent or sludge to worry about with an oven, the ash residue that comes off the cleaned parts must still be handled according to local disposal regulations.

Abrasive Cleaners:

The third process used to clean engine parts involves the use of abrasives. Most abrasive cleaning machines are used in conjunction with other cleaning processes rather than as a primary cleaning process itself.

Cleaning by Hand-- Some manual cleaning is inevitable. Heavy buildups of grease and/or carbon should initially be removed by scraping or wire brushing.

Cleaning aluminum and other soft metals with either technique should be done with extreme care, especially while using a steel scraper or brush. Steel or plastic scrapers are used to remove old gasket material from a surface and heavy sludge. Power tools with a small sanding disc (normally emery cloth) are avail able. These are designed to remove all soft materials without damaging the hard metal surface. After the item has been scraped, an additional cleaning method is used to finalize cleaning.

Carbon can be removed with a handheld wire brush or a wire wheel driven by an electric or air drill motor ( +++0-30). Moving the wire wheel in a light circular motion against the carbon helps to crack and dislodge the carbon. Some shops use a wire brush in addition to another cleaning method.

Wire brushes are also used to clean the inside of oil and coolant galleries. The brushes are soaked in a cleaning solvent and then passed through the pas sages in the block. To do this, the gallery plugs must be removed ( +++0-31).

Abrasive Blaster--Compressed air shot and grit blasters are best used on parts that will be machined after they have been cleaned. Two basic types of media are available: shot and grit. Shot is round; grit is angular in shape. Parts must be dry and grease-free when they go into an abrasive blast machine. Otherwise, the shot or beads will stick. Steel shot and glass beads are used for cleaning and/or peening the part's surfaces. Peening is a process of hammering on the surface. This packs the molecules tighter to increase the part's resistance to fatigue and stress. Steel shot is normally used with airless wheel blast equipment, which hurls the shot at the part by the centrifugal force of the spinning wheel. Glass beads are blown through a nozzle by compressed air in an enclosure.

+++0-33 A vibratory parts cleaner.

+++0-34 An ultrasonic parts cleaner.

Grit is primarily used for aggressive cleaning or on surfaces that need to be etched to improve paint adhesion. However, it removes metal, which can lead to some changes in tolerances. Grit blasting also chews out pits in the surface into which pollutants and blast residue can settle. This leads to stress corrosion unless the surface is painted or treated. These tiny crevices can also form surface stresses in the metal, which can lead to cracking in highly loaded parts. Grit should never be used for peening. Steel and aluminum oxide are the two most common types of grit.

Parts Tumbler--A cleaning alternative that can save considerable labor when cleaning small parts such as engine valves is a tumbler. Various cleaning media can be used in a tumbler to scrub the parts clean. This saves considerable hand labor and eliminates dust. In some tumblers, all parts are rotated and tilted at the same time.

Vibratory Cleaning--Shakers, as they are frequently called, use a vibrating tub filled with ceramic, steel, porcelain, or aluminum abrasive to scrub parts clean ( +++0-33). Most shakers flush the tub with solvent to help loosen and flush away the dirt and grime.

The solvent drains out the bottom and is filtered to remove the sludge.

Alternative Cleaning Methods

Three of the most popular alternatives to traditional chemical cleaning systems are ultrasonic cleaning, citrus chemicals, and salt baths.

Ultrasonic Cleaning--This cleaning process has been used for a number of years to clean small parts like jewelry, dentures, and medical instruments. Recently, however, the use of larger ultra sonic units has expanded into small engine parts cleaning. Ultrasonic cleaning ( +++0-34) utilizes high-frequency sound waves to create microscopic bubbles that burst into energy to loosen soil from parts. Because the tiny bubbles do all the work, the chemical content of the cleaning solution is minimized, making waste disposal less of a problem. At the present time, however, the initial cost and handling capacity of ultrasonic equipment is its major disadvantage.

Citrus Chemicals--Some chemical producers are starting to develop citrus-based cleaning chemicals as a replacement for the more hazardous solvent and alkaline-based chemicals currently used. Because of their citrus origin, these chemicals are safer to handle, easier to dispose of, and even smell good.

Salt Bath--The salt bath is a unique process that uses high-temperature molten salt to dissolve organic materials, including carbon, grease, oil, dirt, paint, and some gaskets. For cast iron and steel, the salt bath operates at about 700°F to 850°F (371°C to 454°C). For aluminum or combinations of aluminum and iron, a different salt solution is used at a lower temperature (about 600°F [315°C]). The contaminants precipitate out of the solution and sink to the bottom of the tank, where they must be removed periodically. The salt bath itself lasts indefinitely as long as the salt is maintained properly. Cycling times with a salt bath are fairly quick, averaging 20 to 30 minutes. Like a hot tank, the temperature of the salt bath is maintained continuously.

+++0-37 MPI testing passes a magnetic field through the iron item being checked.

+++0-35 Examples of stress cracks.

+++0-36 The topside oil artery crack appeared when an oxyacetylene flame was passed over the casting.

Carbon in the flame was trapped in the crack, highlighting it.

+++0-38 A crack will cause two opposing magnetic poles to form on each side; the iron filings used with the magnet will show these fields.

Next: Crack Detection

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