Usage:
Questions have been received about the way bearings function in SR4 Generators, how the bearings are lubricated, and how to repair the bearing bore and shaft.
Function
The rolling element bearing used in an SR4 Generator is supported by a bracket (the large casting on the rear of the generator). The bearing bore in this bracket must be concentric with the frame pilot on the outside diameter of the bracket and it must be sized correctly (see chart). The bearing must slide axially so that no thrust (axial) load will be transmitted to the generator bearing or the engine thrust bearing.
Lubrication
The generator bearing is adjacent to a large cavity that is about 40% full of MPG grease. Bearings may be shielded (not sealed) either on both sides, on one side, or not at all. When a double shielded bearing is used, grease and some oils in the grease bleed past the shield and into the bearing. Excessive grease or oil will go past the outer shield to the outside.
Excessive greasing can occur when the bearing is filled to the point where grease is held in the rolling elements. This causes excessive heat and may lead to bearing failure. Excessive greasing can result in grease being forced past the bearing shield. This normally results in a greasy mess inside the generator, but it can also push the shield out of a single shielded bearing.
Where a single shielded bearing is used, the shield is installed toward the front or away from the grease cavity. Grease from the cavity can go directly into the bearing and it is possible to add too much. The shield will allow some grease to pass to the outside and also protects the bearing from dirt.
The unshielded or open bearing can also be greased excessively. A separate bearing cover is used to protect the bearing from dirt.
Follow the greasing procedure in the Operation And Maintenance Guide SEBU6051 for the correct amounts of grease.
Repair
If a generator bearing begins to seize or if the bearing bore becomes oversized, causing the bearing to spin in the bracket; size the bearing bore and replace the bearing. Metal spray or a sleeve can be used to size the bearing bore. (The dimensions required for the bearing bore are listed in the chart.) Clean out the old grease prior to reassembling the bearing in the bore. Fill the grease cavity with the quantity of grease specified in the chart.
The diameter of the rotor shaft where the bearing is located is also included in the chart. The rotor shaft can be built up as much as 0.25 mm (.010") using metal spray. Then turn the shaft to the finished diameter. Do not sleeve the rotor shaft. The rotor shaft is usually not damaged by a bearing failure.
