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Old 11-15-2012, 10:06 PM   #16
Beemerholics Anonymous
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Joined: Jul 2002
Location: Jackson's Bottom Oregon
Oddometer: 8,083
Originally Posted by mfp4073 View Post
Do rotors go out a bit at a time...meaning do they get LESS efficient and then finally stop working or are they one day they work and next day they fail?

Next, when I got my new brushes in, they didnt have any insulation on the leads. My old brushes did, so I put some shrink wrap on them because it looked like they needed to be insulation from the housing. Thoughts?
Think of the rotor as a chunk of steel with wire wound around it. The rotor accelerates and decelerates with the crankshaft and inertia wants to keep that mass either still or in motion. The steel of the rotor is solidly fixed to the crank so that's not a problem. But that coil of copper wire is epoxied in there and can work loose over time. Then it works back and forth and can either short to the steel or separate causing an open.

Another failure point is where the wire goes through a small opening to the inner sanctum where the coiled wire lives. It can chafe on the opening and ground out there.

Inertia is the enemy here. High temps don't help either.

As for the insulation, I don't recall if they have any or not. The housing is plastic, so there's no conductivity there. I'm sure some insulation wouldn't hurt, just make sure the heat shrink doesn't interfere with the brushes sinking deeper as they wear.
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