Most bottom bracket shells have an internal thread to accept bottom bracket bearing units from numerous manufacturers. If these threads are not in acceptable condition, they may need preparation. Threads may need realignment, or may have weld splatter from manufacturing that prevents the threading of the bearings. Shells may be out of round due to welding during manufacturing. Additionally, some bearing system benefit from having the faces of the shell square to improve bearing adjustment and bearing longevity. If the shell faces are deformed, and are not parallel to one another, the left and right bearing may not be concentric to one another. Machining the shell face improves concentricity.
*All services do not include parts.