avoid the removal of metal from the bottom and sides of  the grooves. When grit-blasting housings, plug all drilled  oil passages with rubber plugs or other suitable material to  prevent the entrance of foreign matter. The decarbonizing solution will generally remove most of the  enamel on exterior surfaces. All remaining enamel should be  removed by grit-blasting, particularly in the crevices between  cylinder cooling fins. Dye penetrant inspection is a nondestructive test for defects  open to the surface in parts made of any nonporous material.  It is used with equal success on such metals as aluminum,  magnesium, brass, copper, cast iron, stainless steel, and  titanium. Dye penetrant inspection uses a penetrating liquid  that enters a surface opening and remains there, making it  clearly visible to the inspector. It calls for visual examination  of the part after it has been processed, increasing the visibility  of the defect so that it can be detected. Visibility of the  penetrating material is increased by the addition of one of two  types of dye: visible or fluorescent. When using a fluorescent  dye, the inspection is accomplished using an ultraviolet (UV)  light source (black light). At the conclusion of cleaning operations, rinse the part in  petroleum solvent, dry and remove any loose particles of  carbon or other foreign matter by air-blasting, and apply a  liberal coating of preservative oil to all surfaces. Magnesium parts should be cleaned thoroughly with a  dichromate treatment prior to painting. This treatment  consists of cleaning all traces of grease and oil from the  part by using a neutral, noncorrosive degreasing medium  followed by a rinse, after which the part is immersed for at  least 45 minutes in a hot dichromate solution (three-fourths of  a pound of sodium dichromate to 1 gallon of water at 180 °F  to 200 °F). Then the part should be washed thoroughly in  cold running water, dipped in hot water, and dried in an air  blast. Immediately thereafter, the part should be painted with  a prime coat and engine enamel in the same manner as that  suggested for aluminum parts. The steps for performing a dye penetrant inspection are: Eddy currents are composed of free electrons under the  influence of an induced electromagnetic field, that are made  to drift through metal. Different meter readings are seen when  the same metal is in different hardness states. Readings in the  affected area are compared with identical materials in known  unaffected areas for comparison. A difference in readings  indicates a difference in the hardness state of the affected  area. Eddy current inspection can frequently be performed  without removing the surface coatings, such as primer, paint,  and anodized films. It can be effective in detecting surface  and subsurface corrosion, pots, and heat treat condition. Some older engines used sludge chambers in the crankshafts,  which were manufactured with hollow crankpins that serve as  sludge removers. The sludge chambers require inspection and  cleaning at overhaul. Sludge chambers are formed by means  of spool-shaped tubes pressed into the hollow crankpins, or  by plugs pressed into each end of the crankpin. If an engine  has a sludge chamber or tubes, they must be removed for  cleaning at overhaul. If these are not removed, accumulated  sludge loosened during cleaning may clog the crankshaft  oil passages and cause subsequent bearing failures. If the  sludge chambers are formed by means of tubes pressed into  the hollow crankpins, make certain they are re-installed  correctly to avoid covering the ends of the oil passages. Due  to improved oils, sludge chambers are no longer used with  modern engines. Ultrasonic detection equipment makes it possible to locate  defects in all types of materials. There are three basic  ultrasonic inspection methods: One of the best methods to double check your visual  inspection findings is to supplement them with one of the  forms of nondestructive testing, such as magnetic particle  inspect, dye penetrate inspection, eddy current, ultrasound,  and x-ray. Defects in nonmagnetic parts (aluminum parts) can  be found by all these methods except for magnetic particle  inspect, which is used for magnetic or ferrous materials (steel).  Flaws are detected by measuring the amplitude of signals  reflected and the time required for these signals to travel  between specific surfaces and the discontinuity. 10-7 3. Resonance 2.  Through transmission 1. Pulse-echo 1.  Thorough cleaning of the metal surface. 2.  Applying penetrant. 3.  Removing penetrant with remover emulsifier or  cleaner. 4.  Drying the part. 5.  Applying the developer. 6.  Inspecting and interpreting results. Dye Penetrant Inspection Eddy Current Inspection Ultrasonic Inspection Structural Inspection Pulse-Echo