How to Maintain Motorcycle with Tapered Roller Bearings

Wheel bearings are constantly subjected to harsh conditions as they take the weight of the motorcycle and rider and the impact from the road while supporting the wheels as they spin at high speeds. Regular checks are essential to maintaining the condition of the wheel bearings, and here's how to maintain them on models with tapered roller bearings, using a 1990s Harley-Davidson as an example.

Harley wheel bearings that vary by age.

Spoked wheel motorcycles have shims and spacer washers built-in on the opposite side of the disc rotor. The grease disc under the inner race is the spacer washer, which is always used separately from the shims for play adjustment.

Harley-Davidson has been loved by many users regardless of model year and model, from the shovelhead that was born in the 1950s to the Evolution, which has many units on the used motorcycle market. In terms of the wheel bearings that support its footing, the models manufactured before 2000 are characterized by the use of tapered roller bearings.

Since the majority of wheel bearings on Japanese motorcycles use deep groove ball bearings or ball bearings, users who have only been tinkering with Japanese motorcycles may be surprised when they take off their Harley wheels and find tapered roller bearings. However, it wasn't just Harley, BMW had models with tapered roller bearings as well.

Comparing ball bearings and tapered roller bearings, tapered roller bearings can support both radial loads perpendicular to the shaft and axial loads in the same direction as the shaft at the same time. This increases the rigidity of the bearing part by supporting rotation with the force applied in the same direction as the shaft. Tapered roller bearings used to be the most common type of front hub bearing for automobiles (today's FWD vehicles have more double-row ball bearings).

In contrast, ball bearings are said to be able to support axial loads in both directions in relation to the shaft to some extent, while primarily supporting radial loads. Basically, they support the radial loads that are applied at right angles to the axle shaft while the grooves between the inner and outer races are in a straight line.

Harley used tapered roller bearings prior to 1999, but since 2000, they have been using ball bearings, just like Japanese motorcycles. Ball bearings have the advantage of being able to be fitted with seals that help to protect the bearing itself from dust and water, which is good for the long life of the bearing.

Tapered rollers must have the right amount of pressure

In the case of this motorcycle, it has three shims built-in. If the bearings are replaced, the position of the press-fit outer race and the inner race will change slightly, so another end-play adjustment will be necessary. By the way, the stock replacement shims, called front wheel bearing spacers, come in five different thicknesses, with the thinnest being 0.038 to 0.064mm.

In order for the tapered rollers to take axial loads, it is necessary to apply the appropriate pressure = preload in the axial direction. In the case of wheel bearings, the outer race of the bearing is pressed into the wheel and the inner race is positioned by a distance collar built into the hub.

When the axle shaft of the wheel is tightened, the inner races are pushed inward against each other (on the center side of the wheel) and the distance collar prevents them from moving inward any further. If the distance collar is long enough, the pressure between the inner and outer races is weakened, and bearing rattling will occur.

On the other hand, if the collar is short, the inner and outer will be pressed tightly together and friction loss will increase.

Harley-Davidson wheels allow the length of the distance collar to be adjusted so that the inner and outer races are properly aligned. Depending on the model year, the distance collars themselves may have different lengths, but in the case of the 1997 model introduced here, a thin metal shim is inserted between the collar and the inner race to adjust the preload.

With the correct shims built-in, it is unlikely that the wheels will need to be readjusted when they are removed to grease up the bearings. On the other hand, if you feel rattling between the axle shaft and the wheel when the tire is lifted off the ground by a jack, you may need to readjust the wheel. However, a certain amount of clearance is also necessary for the wheel to spin smoothly, as zero play can lead to high friction loss and, in some cases, bearing seizure.

According to the service manual, bearing play = end play is specified to be as small as 0.05 to 0.15 mm when measured with a dial gauge.

Deteriorated grease should be cleaned and assembled to the prescribed torque.

If the bearing itself is OK, apply new grease after degreasing and cleaning. If you heap some grease on your palm and dig in with the inner race retainer (roller retainer), you can fill the inside as well as the surface with it. Apply it to the outer race of the wheel hub as well.

When I tightened the axle nut and moved the wheel back and forth and sideways, I felt more play, so I pulled out one shim and reassembled it to check it. The leftmost spacer washer has a stepped inner diameter, and the inner race is in contact with this step.

Removing the oil seal on the front tire of a 1997 Harley-Davidson Sportster allows you to remove the inner race of the tapered roller bearing by itself. This may come as a surprise to Japanese motorcycle users who have only experienced ball bearing type wheel bearings.

The shims that adjust the distance collar and inner race preload are built into the left side of the body, on the disc rotor side. If you look at the owner's manual for this model, you'll notice that the wheel bearing maintenance is described as "change the grease once a year or every 16,000 km or before long term storage", which is a regular maintenance item if you follow the instructions.

Once the inner race is removed, check the condition of the outer race surface that remains on the wheel hub side. If the pressure is right and there is enough lubrication with grease, there shouldn't be any major damage, but if the maintenance interval is too long or the pressure is not right, there may be rust or dents on the surface.

Wheel bearing damage can be surprisingly hard to see when the tire is grounded, so check it by spinning the tire while it's floating in the air. On ball bearing models, you may be able to check it by the rumbling sensation when you remove the wheel and stick your finger in the inner race and turn it, but you can't use this method with Harley-Davidson tapered roller bearings because the inner race will come off when you pull out the axle shaft.

If there is no damage to the outer race, the wheel is greased and restored, but the key here is the tightening torque of the axle nut. It is the tightening torque of the axle nut that determines the pressure preload, which is important for tapered roller bearings; if it is weak, it will cause wobble and if it is strong, it will provide resistance.

The service manual specifies a torque of 68-75 Nm, so this figure must be observed. Then, after tightening, hold the tire in the air and check for proper play. If the magnetic base of the dial gauge is attached to the brake rotor and the tip of the dial gauge is placed against the end of the axle shaft, and the wheel's forward/backward and lateral movement is within the specified range of 0.05 to 0.15 mm, it is normal.

As mentioned earlier, if the bearing is under proper preload, it is unlikely to change its play when the wheel is removed and greased up, but if the bearing is replaced due to damage to the outer race, it needs to be carefully checked after the wheel is set.

After setting the oil seal in the hub and restoring the wheels, tighten the axle nuts to the specified torque of 68-75Nm. We tend to over-tighten the wheels for fear of them coming loose, but the more you tighten them, the more pressure is applied to the inner race and shims, so it's important to use the correct torque.

Hold the tire in the air and move the wheel back and forth and sideways to check the play. The end-play measurement of 0.05 to 0.15 mm is not easy, even if you use a dial gauge. In general, it seems to be judged by whether or not the tire is rotating smoothly and with little backlash.