Once the housing bore has been cleaned and inspected in accordance with the aircraft maintenance manual the new bearing is ready to be installed. The installation tool must push on the bearing at a specific location that does not damage the bearing when installing it into the housing. This is generally accomplished with the same tool as used to remove the old bearing, making sure the bearing is pressed into the housing parallel to the bore in the housing so it is not cantered in the housing.
“If the bearing is installed at even a slight canter you risk damaging the housing,” King says. “Once the bearing is pressed into the housing it needs to be located correctly in the housing bore. Using the proper installation tool ensures this alignment and location is correct.” At this point the bearing is ready to be secured in place by swaging the bearing lip or sleeve.
There are several methods used when swaging the bearing or sleeve; the anvil method; two-wheel roller method; and tri-roller method. The anvil is a piece of metal machined at an angle that under high pressure forms the lip into the housing chamfer. This method is typically used in high production applications.
The two-wheel roller rolls the lip into the chamfer. But care must be taken as this method has a tendency to gall the lip if the wheels skid. The nature of the two-wheel rollers are to roll straight and not in a circular manner. The tri-roller also rolls the bearing lip into the housing chamfer. According to King, the tri-roller wheels actually roll around the lip providing a superior and nondamaging swage and this has become the preferred method for bearing swaging.
Final inspection and testing
Once the bearing has been properly installed visually, inspect the lip for cracks in the swage or excessive galling caused by the installation. In either case the integrity of the lip may be degraded and proper holding force compromised. In addition to a visual inspection there are a few common types of testing methods used to ensure the bearing installation has not adversely affected the operation or rotation of the new bearing: proof load testing and breakaway torque.
Proof load testing is used to ensure the new bearing will handle the lateral forces it sees in service; a check of the installation itself. Proof load testing is typically done according to a process specification, referencing an engineering drawing, or other approved maintenance data.
Breakaway torque is used to ensure the bearing turns or rotates correctly, and has not been loaded or squeezed during the installation process. King says, “Properly testing both the load and torque measurements accurately without damaging the bearing also requires specific tooling.”
“The effects of improper bearing removal and installation can result in many things from damaged housings to premature bearing wear,” King concludes. “The importance of proper tooling used when removing and installing bearings is often times over looked. Incorrect bearing installations will create friction and transmit higher forces throughout the system. This can result in fatigue and premature wear not only on the bearing but other components in the system. Eventually this wear can cause vibration throughout the aircraft, the same type vibration that you were attempting to eliminate by replacing worn bearings.” AMT