Mounting a Bearing: Press on the Ring That Is Being Fitted, Never Through the Balls

A rolling bearing has a load path: from one ring, through the rolling elements, to the other ring. Mounting force must never take that path, because the balls and the raceways are hardened to carry a rolling load and not a hammer blow. Press on the inner ring when fitting to a shaft. Press on the outer ring when fitting into a housing. Drive through the wrong ring and the force goes through the balls, leaving tiny dents in the raceway — BRINELLING — that the bearing then runs over thousands of times a minute. The damage is invisible on the bench and unmistakable in service: a new bearing that rumbles, gets hot, and fails early. It is the commonest way a perfectly good bearing is destroyed before it ever turns.