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Date:         Wed, 5 Dec 2007 13:08:41 -0800
Reply-To:     Pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Pensioner <al_knoll@PACBELL.NET>
Subject:      Sealed Bearings?
In-Reply-To:  <200712040505.lB455YfG020239@flpi098.prodigy.net>
Content-Type: text/plain; charset="iso-8859-1"

Most 'sealed' rolling bearings designed to run in an air environment are 'permanently lubricated'. That is to say the lubricant lasts for the life of the bearing. (reread that sentence, it's catchy)

The 'seal', usually a clip-in, flexible disk with a hole in the middle for the inner race, is designed to keep lubricant 'grease' in the bearing, not really to keep other materials out. The sliding mating surface of the 'seal' is lubricated from within the bearing by a small amount of grease or if it's a French bearing such as found on Citroens, a small amount of 'gras'. The tiny amount of grease at the seal/race junction keeps the seal from being abraded by the shaft and as such weeps a bit of grease. If this lubricant is not present at the junction the seal would quickly wear and enlarge the clearance between the seal and the inner race. The bearing would soon fail under these compromised seal conditions through loss of lubricant. (end of life situation, accelerated by the loss of lubricant, note the second sentence above)

This weeped grease catches external particle contaminants and prevents them from migrating into the bearing itself and as such should be left in place. If you periodically remove this grease, more grease migrates from inside the bearing to the interface. Eventually such fastidious cleaning will cause accelerated failure.

The seal is also effective at keeping water inside the bearing. So no pressure washer or operation/submersion for this kind of bearing as the invisible emulsification of the grease precipitates and end of life situation as described above.

Much has been written about 'sealed bearings' in the Tribology literature and a suitable search will reveal hours of potentially fascinating discourse.

RVC What is the recommended 'sealed/maintenance free' Group 41 battery among those gathered here together? My Delco Freedom is now applying for AARB status.

pensioner


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