The Makita 519411-3 Rotor Assembly (also known as a rotor or armature) is a genuine replacement part for several of Makita's cordless chainsaws. It is responsible for transferring electrical power into rotational movement to spin the saw's chain.The rotor is a central, moving part of the motor made of wound copper, steel, and a cooling fan. It spins inside the stationary part of the motor, called the stator. If your chainsaw overheats, loses power, sparks heavily, or the motor completely seizes, the rotor or its internal bearings may have failed.