You don't want to pump in so much that you blow out the seal, but if you pump slowly and stop just as you hear the air escaping you won't blow the seal.
Another and much better method is to install an automatic greasing unit. One of those cups rervoirs with the spring inside. You can get them from any industrial supply house or thru McMaster-Carr online. The are about $20 and you can install the cup someplace convenient and use a length of hydraulic hose to feed the bearing. The greaser will keep some pressure on the bearing seal to make sure moistrue stays out.
*I had this system on my old Mainship for many years and it worked great.
-- Edited by jleonard on Friday 18th of November 2011 05:59:29 AM