Definition
An abnormal wear pattern on the brushes of a DC generator or motor in which the brush face wears unevenly so that it no longer makes uniform contact with the commutator. The wear is offset from the brush centerline, often caused by a worn or out-of-round commutator, brush holder misalignment, or vibration, and it leads to poor electrical contact, arcing, and accelerated brush and commutator damage.
Plain English
It's when the carbon block (the brush) that rides on a generator or motor's spinning contact surface wears down lopsidedly instead of evenly. Because it's worn off-center, it can't sit flat against the surface, so the electrical contact gets sloppy and starts sparking and damaging parts.
Context Anchor
Seen in aircraft maintenance instructions, especially where a mechanic must make a small alignment or fit adjustment.
Derivation
Eccentric comes from the Greek 'ek-' (out of) and 'kentron' (center), literally meaning 'out of center.' Brushing here refers to the carbon brushes that ride on the commutator. Together it describes brush wear that is off-center rather than even across the face.
Why Pilots Care
Eccentric brushing causes poor generator or motor performance, arcing, and rapid wear of expensive components. For a maintenance technician, catching it early during inspection prevents an in-flight electrical failure and avoids replacing a commutator that could have been saved.
Analogy
Think of a washer with the hole drilled closer to one edge instead of exactly in the middle. If you rotate that washer, the bolt through the hole shifts slightly from side to side.
Intuition Check
Eccentric does not mean strange or unusual here. It means off-center.
Example Sentence 1
During the 100-hour inspection, the technician noted eccentric brushing on the generator and traced it to an out-of-round commutator.
Example Sentence 2
An eccentric brushing in the rudder linkage allowed small changes in neutral position during rigging.