Shop tip: How to mount wheel bearings with the proper fit

TO help ensure proper bearing function, it is important to mount a wheel bearing with the proper fit. Generally, rotating members are installed with tight or press fits (known as interference fits) while stationary components can be either tight- or loose-fitted, depending on the application.

In heavy-duty truck wheel ends, the cup, or outer race, has a tight fit, while the cone, or inner race, typically has a loose fit. Tight fits keep the rotating bearing components (cup) from turning in the housing (hub). When the bearing cup turns in the hub, it wears away the hub inside diameter (ID) and backing shoulder, creating debris particles, which can cause seal wear and leaks; bearing race, rib, and roller wear; and weakening of the hub. These wear particles also can oxidize in the lubricant.

Wearing of the hub ID (at the bearing locations) also increases the hub bore and results in out-of-tolerance hub. For this reason, the hub ID should be measured when the bearings are removed for service. If the hub ID is larger than the OEM's specification, the hub should be replaced.

Loose fits are used on the stationary component (cone). The loose fits are used primarily to accommodate ease of assembly and bearing adjustment. The loose fit allows the cone to easily slide along the shaft as the nut is tightened during bearing adjustment. Excessively loose fits should be avoided or misalignment may occur within the wheel-end. Misalignment will prematurely wear out the bearings and seals. Similar to the hub ID, the spindle diameter should be measured during wheel-end service to ensure that there is not excessive spindle wear. Inspect the top and bottom of the spindle because the under side may show wear when the top half appears new. If the spindle diameter is out of the original manufacturing specifications, the spindle should be replaced.

Warning: Proper maintenance and handling practices are critical. Failure to follow installation instructions and to maintain proper lubrication can result in equipment failure creating a risk of serious bodily harm. Never spin a bearing with compressed air. The rollers may be forcefully expelled, creating a risk of serious bodily harm.

This information is provided by The Timken Company, an international manufacturer of engineered bearings and alloy steels.

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