chiwia | & | [| { 8 | ELECTRIC ” TECH TIPS Bearing Failure Analysis Have you ever looked at an alternator core or customer return with the bearings destroyed and questioned what the possible causes are? For years | had questioned how can | tell if it was the way the bearing was installed, the bearing or a vehicle related issue? Of course, when | would return bearings to a supplier | would get really vague feedback, typically something along the lines of “it was not the bearing.” Emerson Bearing had put together a really excellent Bearing Failure Analysis presentation that was easy enough for me to follow. They were kind enough to allow me to pass on their information. Sketch of Failure Picture of Failure Description Cause Loose fit, causing inner or outer race to move, resulting in fretting. Fretting occurs when fine metal particles oxidize that result in a telltale brownish colour. Shaft worn and undersized or housing bore worn and oversized Discolored, wide ball path at bottom of raceways. Preload failures will appear as heavy, wide wear patterns in the bearing races. Typically an oversized shaft or an undersized housing bore would cause this. The excessive interference fit generates a preload on the bearing and results in abnormal heat and wear on the race. Electrical Fluting will appear as lines perpendicular to the bearing race. This will occur if current flows through the bearing instead of a proper ground route REV: 20090918 Courtesy of Emmerson Bearing Dixie Tech Tips are intended for use by professional technicians, and are not for the general public. They are written to inform technicians of conditions that may exist or as a guide to aid in diagnosing and servicing a vehicle. All references to original TSB_002.doc equipment manufactures, vehicle manufactures and any other Trade Mark names are for the sole purpose of identifying the vehicle and or part that the Tech Tip applies to. This document is property of Dixie Electric Ltd. and is not to be copied or distributed with out written permission.