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Engine Building Fundamentals: Crankshaft Polishing

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Crankshaft Polishing

01.44

00:00 - The surface finish of the crankshaft journals is critical to the reliability and life expectancy of the engine bearings.
00:07 While a brand new crankshaft should offer a perfectly smooth journal finish that's ready to drop into the engine block, second-hand crankshafts may show some minor scoring or damage to the journals.
00:21 In some cases, this damage may require the crankshaft journal to be ground to a smaller size to remove this damage, which we'll discuss separately.
00:30 However, often, light scoring can be removed by polishing the journal.
00:34 Polishing is achieved while the crankshaft is installed in a crankshaft grinder so that it can be rotated about the journal axis.
00:43 A fine, abrasive belt is then run against the crankshaft journal as the crankshaft rotates.
00:49 This process polishes the journal and removes the light score marks.
00:55 Typically, the amount of material removed during the polishing process is very minimal, so it has little effect on the final bearing clearances.
01:04 However, this still needs to be considered when any polishing is performed.
01:10 Your machinist will be able to advise as to whether damage to your crankshaft will be repairable by polishing, or whether grinding will be required.
01:20 A good indicator of the severity of damage to a journal is to run your fingernail across the score marks.
01:27 You'll be surprised that sometimes, visible scoring can't actually be felt with this test.