A bearing is a device or tool used to promote constrained circular or linear motion. In the case of a stationary bike, the front and back wheel each have externally located bearings that are prone to wear and tear. While they are sealed to promote its lifespan, they can become loose over time. At this point, it is necessary to replace those bearings. With the proper tools and equipment, removing the pedal crankset to replace the bearings is a cinch.
Put the flywheel tension at its least resistance. Using either an open-end wrench or an Allen wrench, dislodge the bolts found on the cover of the flywheel. This will free the cover so that the belt of the stationary bike is exposed.
Free the belt from the pulley by unhooking the belt adjustment clasp. Take off the cap found at the left side crank arm. This will show the attachment nut, which will need to be removed by using a crankset socket wrench. Rotate the wrench counterclockwise on the left crank arm to release the nut.
Loosen the bolts found at the left side crank arm using an Allen wrench. Take off the crank arm so that you can see the cone and the bearing. Remove both the cone and the bearing by gently tapping the shaft on a hard surface and slide out the bottom bracket off the shaft. Using solvent and a cloth, clean both the shaft and the bottom bracket.
Rub some grease on the new bearings before sliding the cone and bearing onto the shaft followed by the bottom bracket.
Put the left side crank arm back onto the shaft and use an Allen wrench to tighten the bolts. Position the nut on the crank arm and secure it into place using the crankset socket wrench.
Put everything back in its original location. The belt should be placed over the pulley and adjusted so that it is at a medium-resistance level. Place the cover over the pulley and secure it into place by tightening the bolts.
Each stationary bike model is different. For specific instructions on replacing the bearings on your bike model, refer to the manufacturer's guide or contact their support team if you bike is under warranty.