Turn off the breaker switch for the swamp cooler at your main fuse panel, then turn off the swamp cooler switch. Place a ladder on the side of your house, if you have a roof-mounted swamp cooler unit. Locate your swamp cooler cowl and find the access panels to the motor assembly and belt and the rear of the main driveshaft. The entire swap cooler cowl might come in one piece, so use a screwdriver to loosen and remove all of the cowl screws. Set the cowl aside.
Look for the bolts that hold the motor down to the frame -- they will have bolts on the top and nuts on the underside. The motor has an adjustable frame mount, so make a note of where the bolts are located, so you can align it properly. Loosen the motor mount bolts, but do not remove them. Shove the motor on its adjustable slots and pull off the fan belt.
Take a scratch awl and etch a small mark where both bearings are attached to the driveshaft -- this will help to reposition the new bearings on the shaft. Use a socket and wrench to remove the two bolts on the front bearing bracket. Pull the bracket off. Use a socket to remove the two bolts on the rear bearing cap; remove the bearing. Pull the driveshaft straight out from the front of the case.
Sand the entire length of the shaft with some fine emery cloth, removing all rust, dirt and corrosion. Wipe the shaft down with a rag, then smear oil over the shaft from the front to the back. Use a hammer to tap both bearings off the back end of the shaft, starting with the rear bearing. Sand the bare spots where the bearings contacted the shaft and oil the spots.
Use the hammer to tap a new bearing on the shaft, and do this gently. Tap the bearing far enough to align it with your scratch awl mark. Use the hammer to tap the second bearing on the shaft, aligning with your mark. Place the bearing caps over the bearing and align the shaft, so the bearing bracket mount holes line up. Insert the bearing bracket bolts and tighten one bearing at a time, alternating back and forth between the two bolts. Tighten the second bearing in the same manner.
Slip the fan belt over the motor and pull the motor in its adjustment slots until you have tension on the belt. Partially tighten the motor mount bolts, making sure the fan pulley is aligned with the motor pulley. Push the belt with a finger to acquire about 1/2 inch play of deflection -- this is the proper belt tension. Tighten the motor mount bolts with a socket. Place about five or six drops of oil in the bearing cap oil holes, which are on the top of the caps.
Replace the swap cooler cowl panels, or one-piece cowl unit, and align the holes. Start all the cowl screws in by hand. Tighten the screws with a screwdriver. Turn on the breaker fuse, then turn on your swamp cooler. Go back to the swamp cooler and listen and look for smooth operation.