Replacing Spun Motorcycle Bearings

After a few track days Steve's motorcycle felt sluggish and notchy when falling into turns. With the rear tire in the air, Steve grabbed the rear rim at 3 and 6 o'clock, pushed with his left hand and pulled with his right hand and determined the cause of the problem. The symptoms of a spun bearing are straightforward to diagnose and include: a notchiness felt when moving or spinning the bearing; the bearing moves with difficulty; and a noticeable deflection is felt when lateral force is applied to the bearing. First, use a set of calipers to measure the bearing's inside and outside diameters as well as its depth. Armed with this information, look in a local directory for a local bearing house and see if they carry your bearing in stock. Wheel, suspension and swing arm bears are frequently a generic size and can be had for a fraction of the manufacturer's asking price.

Once we have our new bearing we put the bearing in a freezer overnight to get the bearing to shrink a few thousands of a millimeter. Removing the old bearing is a slow process but if you strike the outer race of the bearing a brass punch the bearing will eventually come loose. If you strike anything other than the outer race it will knock the ball bearings loose, potentially wedging the bearing in the cavity. Once the bearing is removed, clean the cavity with some emery cloth until the metal is smooth to the touch. To aid in the new bearing's installation we go to a hardware store and buy some thick washers that are the same size as the bearing's outer race. Note that the washers cannot be larger then the outer race as they wouldn't be able to fit in the cavity and they cannot be smaller than the outer race as the installation process would damage the new bearings. We put the bearing in the freezer to give us a couple of thousandths of a millimeter and will do the same to the rim to make the bearing fit easier.

Using a propane or butane torch we heat the rim's hub for a few minutes to expand the cavity a few thousands of a millimeter. Although a propane torch will not get hot enough to melt steel it could get hot enough to deform aluminum, which would be bad. Do not leave the torch in one place but sweep the flame around and across the hub's cavity to equally disperse the heat. Once the hub is warm we get our frozen bearing and drop the bearing into the heated cavity. If you have heated the cavity enough, the bearing will fall in and make a sizzling sound akin to the cooking of bacon. Using leather gloves, install the correctly sized washer over the bearing's outer race and place a heavy-duty socket overtop the washer. Strike the socket with sharp blows of a hammer to get the bearing to fall completely into its cavity. Once the bearing is seated correctly, take a ruler and measure the distance from the bearing's outer race to the edge of the cavity to ensure the bearing is evenly seated against the hub. If the bearing is flush, install your rear wheel in the reverse order from which you removed it. Torque all the important bolts and ride faster, with the piece of mind that your motorcycle is spinning faster and easier.

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