Cleaning engine parts is one of the most basic procedures that your machine shop will do, yet it is also one of the most important parts of the engine repair procedure. Before you can really inspect the parts for your engine to determine what will need to be done to them, they have to be cleaned. If the parts aren’t clean, it’s hard to measure them and inspect them for defects etc.
If you are restoring an engine and want it to look original, then it must be completely cleaned of all rust, old paint etc so that you can refinish it after it is assembled.
Cleaning engine parts is also one of the most time consuming parts of the engine repair procedure so anything that can be done to make it easier will help reduce costs.
There are several methods that are generally used to clean parts in a modern Automotive Machine Shop.
Most shops have a “spray washer” that is used for quickly cleaning engine parts prior to inspection. This machine is basically a big dishwasher type of cabinet that has a strong soap and hot water solution in it. The parts are placed on a turntable and the solution is sprayed at them under very high pressure. This gets most of the oil, grease and other road dirt off the parts so that they can be worked on. This is what we use to clean cylinder heads before we check them for cracks and resurface them. We also use this machine to rinse engine blocks after machining to remove honing oil etc.
Hot tanking is the traditional way to clean dirty cast iron engine blocks, heads etc. The hot tank is just a big metal tank with a very nasty, caustic hot water solution in it. The parts are submerged in the solution and allowed to soak for many hours with the solution slowly circulating around them. This is sometimes referred to “vatting” or "boiling" the block, because it is being soaked in a large “vat” of almost boiling liquid. A hot tank does a good job of cleaning engine parts but does not always remove all of the rust and old paint. Because of environmental rules and regulations, a lot of shops are doing away with this method of cleaning.
Aluminum parts cannot be cleaned in a hot tank as they will dissolve.
Thermal cleaning of engine parts has been used in the automotive machine shop business for at least 25 years or so. In this method the parts are loaded into a large oven and baked at a temperature of about 500 degrees. This basically burns off all of the oil, grease, carbon, old paint etc. This is very similar to using the self cleaning cycle on your home oven. Some of these ovens will bake the parts for 7 to 8 hours, while others are constructed differently and use an open flame which can do the same job in about an hour.
Once the parts have been run through the oven, the next step is to put them in another machine called a steel shot blaster. This machine bombards the now dry parts with very small steel beads. This removes any remaining rust, paint etc as well as the burnt residue of oil and carbon. Once the parts come out of the shot blaster, they look like brand new castings.
One last very important part of this cleaning method is to “tumble” the parts in order to remove any remaining steel shot. Even the smallest particle of shot can cause damage to a new engine so it is imperative that every bit of it is removed. Some shot blasters have a tumble cycle built into them while others require the parts to be put in a separate tumbler that rolls them around to remove the shot. This is the type of system we use and have not had any issues with the steel shot.
The other very real advantage to this method is that there is no dirty cleaning solution to have to dispose of. All you end up with is some fine dust from the shot blaster and it can be disposed of in the trash.
Instead of an oven some shops will use a spray washer with a very strong caustic solution in it to clean the parts prior to shot blasting them. This method seems to work well as long as the parts are completely dried prior to shot blasting.
Cleaning engine parts with a glass bead cabinet has been done for many years in many industries. It is really the best way to clean aluminum cylinder heads even though the process of making sure that all of the glass bead particles are removed from the parts is VERY time consuming. This process also works well for many small parts such as engine valves.
Soda blasting is a relative new process, especially for cleaning engine parts. It is very similar to using glass beads, but instead a specially made “baking soda” is used. This soda is coarser than that used at home and does a very good job cleaning parts without hurting the underlying metal in any way. Another advantage to using soda is that it easily dissolves in water so that a quick rinse is all that is needed and you don’t have to worry about left over cleaning material hurting your newly machined parts. This seems to be the up and coming method to clean parts, especially aluminum cylinder heads.
This is the same method that the jeweler uses to clean your Wife’s diamond rings.
Ultrasonic cleaning uses sound waves to create millions of small bubbles in a tank of cleaning solution. The parts to be cleaned are submerged in the solution and as the bubble are formed and “explode” they remove any dirt, grease, carbon etc. This method also works very well. The one disadvantage that I noticed with ultrasonic cleaning is that aluminum parts do not come out of the cleaning tank looking like new. They seem to have some discoloration to them even though they were clean. If you are going to paint the parts then this shouldn't matter.
Most shops will also have a traditional parts washing sink in which a cleaning solution is circulated through a hose with a brush on the end and is used to manually clean parts. There are times that this is the only method that will really work.
We used to clean valves and some other parts in a parts tumbler type of cleaner. The parts would all go in a basket filled with large steel "beads" and then it would tumble everything together while submerged in solvent. This method worked well but I never liked the fact that it scarred up the valve stems somewhat. They do make little sleeves that you can put over the stems but its a lot of work. We find it easier and faster to just rinse the oil off the valves and then glass bead them. I can clean a set of V-8 valves in about 5 minutes this way and there is no damage to them.
So that gives you an idea as to the ways that your machine shop will clean the parts to your engine.
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