Engine Decarboning: Piston Cleaning
WARNING: The author of this page is not a professional or certified aircraft engine mechanic. The information contained herein constitutes a description of the writer's experience only and should not be construed or interpreted by the reader as instructions or guidance for the successful completion of any repair or maintenance procedure. Use of any information contained herein is at the user's own risk. This information has not been reviewed, evaluated, or approved by the manufacturer of this engine.
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As with the heads,carbon deposits are removed from the piston surfaces with the wood dowel scraper followed by a scotchbrite pad and kerosene.
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A piece of soft brass flat stock sharpened with a file makes an effective tool for cleaning out the ring grooves. Burnishing a hooked edge onto the square end of the same brass flat stock makes a miniature scraper that can be used to clean the top and bottom surfaces of the grooves - the part that the ring bears against as the piston moves up and down in the cylinder. It's important that all three surfaces be clean right into the corners of the groove. It's this stuff in back of the rings that pushes the rings out reducing their clearance to the cylinder walls and leading to the possibility of seizure. If you've got heavy contamination, an overnight kerosene soak will soften the crud and make complete removal easier. Use only solvent and a soft rag to clean up the sides of the pistons. You don't want to remove or degrade the fine machined surface on the piston skirts. |
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A soft brass wire brush and kerosene can be used to do the final cleaning of the ring grooves. If you experienced difficulty removing the wrist pin you should also clean inside the wrist pin bores in each side with kerosene and a coarse rag. It'll make reassembling that pesky needle bearing a lot easier if the pin goes in with just light hand pressure. Also: not pictured is cleaning out the crust of burned on oil residue which you will find on the underside of the piston crown. This scrapes out with the sharp edge of the dowel tool. Finish up as before by washing with water and detergent and drying thoroughly.
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The flat brass scraper is used to clean carbon from the rings as well. You'll want to suppport them on a smooth flat surface and hold the ring firmly close to where you're working on it. Cleaning is straightforward but be sure to get right into the inside corner of the top ring as well as all the way around the inside edges. Avoid scraping or abrading the molybdenum bearing surface on the outside of the rings. |
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