Engine Design
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Cleaning an Engine

Cleaning an Engine

Cleaning. Something always dreaded, often started with the best intentions, but soon after becomes a corner cutting experience. Cleaning is tedious, dirty and something no one truly enjoys doing. The more that is done automatically the better. However; in a lot of cases, cleaning equipment is not available and requires manual labor to complete the task. This is where the corners are cut. The more that can be done without the manual part, the better.

All engines get dirty. Both inside and out. Typically, carbon deposits are present on the inside and the outside has dirt, oil and years of a mix of the two. Cleaning is the necessary evil task that has to be done for many reasons. You need to know what is underneath all of the gunk. Are there cracks, failures etc.? You do not want to transfer that gunk to your machining equipment and, quite honestly, who wants to handle dirty parts?

Most shops in this business have invested heavily in cleaning equipment. Solvent tanks, hot water wash tanks, blast cabinets, heating ovens, ultrasonic tanks, etc. The DIY builder has to resort to shop bought cans of degreaser and lots of hand cleaning. After it is all done, with loads of empty cans and trash bins full of dirty paper towels, the parts still look less than desirable. The other choice is to take them to a shop that can clean the parts for you. Although, you rely upon their idea of what is clean. Most will run them through a hot tank cycle and give them back, which can only be described as washed.

So, to understand the cleaning process, the definition of clean must first be understood to then know how much time is required. Typically cleaning can be as much as 30% of the whole rebuild time. In some cases, even more time is required.

Cleaning engine parts, for example Porsche engine parts, is extremely important. The major parts of the engine are made from cast aluminum. These parts have to be crack checked using a zyglow inspection solution and a black light or some sort of dye penetrant. If the part is still dirty then the inspection is compromised and the cracks may not be visible.  Maybe the engine had a water or oil leak and inspection to find some sort of porosity is required.  Cylinder heads covered in years of dirt, oil and carbon crushed combustion chambers require lengthy cleaning times. Once the dirt and oil is removed, removing the stubborn carbon can be tedious and require multiple attempts to remove. Looking for cracks around exhaust guides inside the exhaust port would be very difficult if the port was still covered in carbon.  Measuring the chamber volume, piston to head clearances, will be compromised if the surface is still covered in carbon.

The engine cases do not see the heat cycling that the heads do, so cracking is not as common. However, Porsche engine cases are known to crack through the #7 main saddle where the saddle is wasted away. Making sure that all sealing surfaces are clean is critical to ensure on assemble there are no leaks.


Every place that offers a cleaning service has different ideas and equipment. There is no one way to clean, but there is only one definition of truly clean. Unfortunately, this has turned into a gray definition. Clean used parts should look just as if they were first manufactured except for some discoloration.

If the shop cleaning your parts has respect for their equipment and wants to offer good service, they will usually clean the heavy gunk from the parts being clean by hand first. Once all of the heavy stuff is removed and scraped as clean as possible, the part will be soaked and washed with solvent or some cleaning solution in a tank. This will remove the last of the gunk not removed by hand. Then the parts may be washed in a hot tank with a solution of industrial detergent and hot water. These hot tanks are typically a rotisserie type that give the parts a good cleaning on all surfaces. After this process, the parts can either be cleaned by some sort of media blasting, heat cycling with media tumbling. Cylinder head ports and chambers usually require the media blasting to remove the stubborn carbon deposits. This can be with either hard or soft media. Typically, with some grade of glass bead, (hard) or a soft medium like walnut shells or soda.  Ultrasonic cleaning is very common nowadays and this process is done as well. It can be either done in place of many of the above processes or in combination. We do this after all of the other processes are performed and often multiple times during the rebuilding sequences. Before final assembly we always pass the parts through this process to ensure the parts are absolutely clean. We perform these processes in this order for one reason. We want to keep our cleaning solutions as clean as possible for as long as possible. If you try to clean dirty parts with dirty solutions, you are wasting your time.

If there is any machine repair required, working with clean parts is always preferred. No machinist wants to touch parts that are covered in grease and oil. Nor do they want their machine tools covered in your gunk. After any machine work is performed it is essential to clean the parts thoroughly. This requires hot, soapy water, as detergent is the only solution that removes honing or grinding remains. The parts should be washed until a clean white cloth can be rubbed on the parts and remain clean. Also, if the heads or any other part was blasted with glass bead or some other shot media, it is absolutely essential to ensure no media blast remains trapped inside any part. Once the parts are cleaned they should be bagged to remain clean prior to any disassembly or machine repair.


This work takes time and costs money. Unfortunately, much of the cleaning done by some is based upon time spent and not the end result. I have seen Porsche heads that have been repaired and the ports are still covered in carbon. It can only be assumed that they were never crack checked. The cleaning of an engine and its parts is the single biggest labor operation in the rebuilding of an engine. Something that can be used as a gauge for the level of work you can expect from a business is the attention to the cleaning process. If they take care and time to make sure the parts are thoroughly cleaned and inspected, you can surely count on all of the other areas to be given the same level of attention, care and quality.


Remember, an engine is the sum of its parts and if those parts are not up to a level required, the engine will suffer.