We all know the challenges involved with justifying the purchase of additional or specialized tooling, particularly if the tooling is not a high-use item. How often have we heard comments like, we don’t want to spend the capital to purchase this special tooling. We may only need it a few times. Often times this is followed by, as a result of not buying the correct tool we now have to make a repair to the item. And of course the most popular phrase among aircraft technicians has to be the phrase, the right tool for the right job.
Improvising when it comes to special-use tooling is commonplace in aircraft maintenance, and many times this works well. Aircraft mechanics are resourceful and take pride in crafting their own special tools. How many of us have used sockets and a bench vise to force a worn bearing from its housing, and then use the same innovative method to install the new replacement?
Proper bearing installation is a critical task which has a high cost in both time and materials and has become a major focus and concern of the prime airframe manufacturers. Proper bearing installation can affect both aircraft performance and safety, and for technicians and maintenance organizations deserves a second thought before your improvised tooling causes damage resulting in further repairs.
To learn more about the basic function of a bearing and proper removal and installation I turned to Scott King principle with King Industries. King began by saying, “First, think of a bearing as the sacrificial part of any mechanical system. A bearing is designed to see wear, it will wear, and it is designed to eventually be replaced so that other major components in the system do not need to be replaced.”
According to King you can generally place bearings into two primary groups. The first type of bearing provides rotational ability for a part in a system and reduces friction created by a full rolling element. These bearings are considered rotational, they are subject to high radial loads, and are generally secured in a housing using a staking method that displaces housing material over a chamfer in the outer race of the bearing. This can be accomplished by either rolling the housing over the bearing or staking the housing with a ball or line impression.
The second primary use of bearings in aircraft is for positioning of attaching components, such as a movable flight control like an aircraft rudder. These bearings are not rotational and subject to higher lateral loads. They are secured into place by either swaging a groove that is in the outer race of the bearing into a chamfer in the housing, or swaging a sleeve into the chamfer on the bearing and in the housing.
Removing and installing a swaged in place bearing
King says, “Many times proper tools for bearing removal are overlooked. Weakening the lip by cutting is critical.” When removing a grooved bearing that has been swaged in place, the lip must be weakened in order to remove it and press out the old bearing. Care must be taken to ensure the cutter doesn’t damage the housing, and that the old bearing does not scratch the housing when being pressed out of place.
Weakening the sleeve or lip in order to remove the bearing can be done in several ways; grinding or machining the swaged lip; using a drill press or milling machine with a hole-saw style cutting tool; or using a hole-saw style portable cutting tool. Using the portable tool is the preferred method as it provides access to the component on the aircraft, and more importantly it ensures proper alignment of the cutter so it does not damage the housing during the cutting process.
At this point the bearing is ready to be pressed out of the housing using a removal tool. The proper removal tool should be of a size and design that ensures the cut lip does not scratch or damage the internal surface of the housing bore when pushing the bearing out.
Cleaning, inspecting, and bearing installation