James I would argue that Pedro may not be completely correct. While the thermal dynamics of heating and cooling are certainly correct I suspect there is a problem with the gas law. During the cooling cycle there are 2 phases in contact with the bearing, a gas phase and an oil phase. Since fluid flow is always to the path of least resistance then the gas phase must preferentially move through the bearing during heating and cooling cycles before the viscous oil. I suspect this eventually pushes out the grease and causes the seals to fail, then the oil simply equalizes through the bearing by gravity. A sealed bearing could very well be fine if there was a vent hole in the IMS shaft. Just my thoughts.
|