When lubrication fails, the first point of distress in a high-speed ball bearing occurs at the rolling contact between a ball and a race. Because of the curvature of the race, sliding as well as rolling must occur in the contact area. Hence the absence of an oil film results in friction and heat. The localized heating and resultant differential expansion of the parts cause preloading of the bearing owing to loss of internal clearance. This process progresses rapidly to cause spalling or pitting of the races and balls, skidding balls, broken ball separators, and a jammed bearing.