By Tim Timmerman, Manager SR2X Engineering
The Enviro air conditioning system compressor assembly mounts to the back of the engine. The drive shaft hub assembly is part of the lower assembly that is driven directly by the engine. A pulley is bolted to this drive shaft hub assembly, which through a belt drives the compressor. When this compressor was originally designed, there was no maintenance provision for the drive shaft hub assembly.
Service experience revealed that the original rubber bushings which surround the four drive shaft mounting bolts wore down prematurely resulting in a metal on metal condition. This metal on metal wear results in either a shear failure of those four drive shaft mounting bolts or a worn out bearing. Both of which require the replacement of the entire drive shaft hub assembly because of the significant damage. A timely solution to the root cause problem of premature wear of the rubber bushings was not possible, so to prevent the more significant repair and replacement, the rubber bushings and guidance for the removal of the drive shaft hub assembly in the field to replace those bushings was provided.
A definitive redesign of the drive shaft hub assembly is now available as a spare for the field. This new design makes several configuration changes and replaces the existing rubber bushings with a three-piece design that will be far more robust than the original configuration.
The AMM specifies 100 hour inspections of this part, and it is highly recommended that those who experience field issues with the rubber bushings wearing out replace the entire drive shaft hub assembly as this will solve the root cause problem. However, Cirrus will continue to make the rubber bushings available for those who do not mind making regular on-condition replacements.
If you have any questions about this or any other engineering topic contact Tim Timmerman at email@example.com