170  

Figure 10. Pre-Load “Record Grooving” 

3. Assembly evaluations also identified a built in  misalignment caused by the inner gimbal covers  distorting the inner gimbal structure and alteri ng the precision bearing bore alignment. This bore  misalignment exacerbated the wear observed on t he steel sleeves of the Bearing Housings.   CMG3 Forensic Findings

The most notable observation was t he excellent condition of both Inner Gimbal spin bearings. In general,  the HR side spin bearing was in good condition. An abund ant amount of lubricati on was noted in the ball  race contact zone and at the retainer pad and inner race land interface. The balls were bright with some wear tracks, i.e., frosted bands, composed of rep eated dents most likely caused by hard particles  embedded in the raceway. The inner race was not significantly worn. It contained glazed bands but not beyond the original surface finish. The retainer was not damaged. It contained very light deposits around  the ball pocket. Some amount of de-wetting was noted on the inner and outer raceways, but not on the  balls. Gas Chromatography/Mass Spectroscopy (GC/MS ) analysis of the lubricant by The Aerospace  Corporation showed good correlation to unused KG80 oil.  However, long chain fatty acids and plasticizers  contaminats were identified. The burnishing and slight deposition of the darkened lubricant, more on the fore and aft portions of the pocket than on the si des. indicates this bearing may have operated with  periods of mild retainer instability. The failure investigation team  consensus is that this bearing was in  good shape with wear commensurate with its 5.8-year life and not a contributor to the observed  anomalous accelerometer signature.  Initial visual observation classified the SM side bearing in comparatively worse condition than the HR side bearing but still acceptable. An abundance of lubricat ion was noted in the ball race contact zone and at  the retainer pad and inner race land interface. The balls were bright, with wear tracks and the oil was beaded as droplets (evidence of dewe tting). Some wear tracks are comp osed of metallic wear debris and  some grooves due to mild surface distress. Some patch es of the balls are rich in sulfur. Other bands are  composed of repeated dents most likely caused by  hard particles embedded in the raceway. The inner  race contained a significant wear track and glazed bands due to mild surface distress. The retainer was not damaged. Deposition of darkened lubricant was observed on the fore and aft portions of the pockets. Only two of the inboard and outboard quadrants contained minor accumulations of slightly degraded lubricant. The Aerospace Corporation GC/MS Analysis of the lubricant showed good correlation to unused KG80 oil however “contaminants” like long  chain hydrocarbons, long chain fatty acids and  plasticizers were more predominant in this bearing. The failure investigation team consensus is that this bearing is in worse condition than the HR bearing, but still acceptable, it contained more wear but still  commensurate with its 5.8-year life. It had higher co ncentrations of contaminants and more areas of dewetting, including the balls. It is believed that this we ar was accumulated over the life of the unit and not  NASA/CP-2010-216272