Of Grease and Ball Bearings

Having cleaned and regreased my share of bearings over the years, I have always wonderd:
How long does the grease 9that you loaboriously pack in) actually stays within the beaing surfaces?
It seems to me that after a few hours under load and turning, the grease moves to the outside of the bearing races-does anything actually stay on the mating/contact surfaces?

The way I understand it, the grease itself isn’t what does the lubricating, it’s the oil in the grease. Grease is an oil and a thickener, usually a light metal soap, like lithium-complex, to name a very common one.

As the grease works, it releases some of its oil, which does the actual lubrication, and it soaks some of that oil back up when it’s not in use.

Combine that with the usual pretty large amount of grease (frequently under a small amount of pressure) in a greased fitting/bearing and high temperatures, and enough of the oil ends up getting back into the moving parts to keep it adequately lubricated.

Also note that high speed ball bearings should not be filled with grease…just a small amount. Too much grease churns and heats up causing failure. You can spot this because the retainer cage ends up getting blued from the heat.

Often the only difference between the normal and high speed versions of a bearing is the type and amount of grease.

If you are talking about your bike, feel free to over grease. Less is best with auto wheel bearings.

I wondered the same thing and concluded that pretty quickly all but a tiny fraction gets dozed out of the path.

Greases are generally soaps with oil in them, but I don’t think they are typically metal based soaps. When they are, it’s more expensive, and they advertise it - hence “lithium grease” which costs more.

I haven’t heard that the soap soaks up the oil and redispenses a little but it’s plausible.