3-8.It is imperative to clean all engine parts thoroughly to facilitate inspection. Two processes are involved in clean-ing engine parts; degreasing to remove dirt and sludge(soft carbon) and the removal of hard carbon by decar-bonizing, brushing or scraping and grit-blasting.
3-9. Degreasing. Degreasing is accomplished by immers-ing or spraying the part in solution of white furnace oil (38-40 specific gravity) or a suitable commercial solvent such as Varsol or Perm-A-Chlor. Operators are warned against the use of solvents with which they are un-familiar, since there are may products on the market which are injurious to aluminum and magnesium. Ex-
treme care must be exercised if any water-mixed degreas-
ing solutions containing caustic compounds or soap are
used. Such compounds, in addition to being potentially
dangerous to aluminum and magnesium, may become im-
pregnated in the pores of the metal and cause oil foaming
when the engine is returned to service. When using water-
mixing solutions therefore, it is imperative that the parts
be completely and thoroughly rinsed in clean boiling
water after degreasing. Regardless of the method and
type of solution used, coat and spray all parts with
lubricating oil immediately after cleaning in order to pre-
vent corrosion.
3-10.Removal of Hard Carbon.While the degreasing solu-tion will remove dirt, grease and soft carbon, deposits of hard carbon will almost invariably remain on many in-terior surfaces. To facilitate removal, these deposits must first be loosened by immersion in a tank containing a decarbonizing solution (usually heated). A great variety of commercial decarbonizing agents are available, includingsuch products as Gunk, Penetrol, Carbrax, Super-Chemaco, Gerlach No. 70, and many others. Decar-bonizers, like the degreasing solutions previously men-tioned, fall generally into two categories, water-soluble
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