|The MGA With An Attitude
HEATER MOTOR TECH - ET-212 - Pg 7 of 7
There are still a couple of points missing from this story, perhaps the most common of which is that the carbon brushes can eventually wear out, or the bearings could go bad. Like most of the rest of the car, these motors are happiest when they run regularly. Mine runs most of the time, either for heating or for ventilation, probably in excess of 80% of the time the car is being driven, and I drive it a lot. I cleaned and oiled these bearings and replaced the brushes once during the car's restoration when it had about 150,000 miles on it. Twelve years and 140,000 miles later it got new brushes and a few drops of oil again, but only because it was convenient when the heater motor was apart again because the armature had burned out and needed to be rewound.
Occasionally the small shaft bearings can give some trouble in service. They are porous sintered bronze bushings that should be impregnated with a little oil that wicks out onto the surface to keep the shaft oiled. They are generally very long lived under these light load conditions. I have fried a couple of these motors over the years for other reasons, but have never had one actually wear out the bushings. One problem can occur if the oil dries out, or if the bushing runs hot and bakes the oil into a hard coating, in which case the motor can make a loud squealing noise when running. This condition may be most noticed on first start up in cold weather and is aggravated by long periods of storage. Often this can be cured with a couple drops of oil on the bushing at the output end of the motor without having to disassemble it (except perhaps to remove the fan from the shaft). If there is oil badly baked on the bore of the bearing, a good soaking in penetrating oil may ultimately cut through the grime to clear the pores and renew the oil wicking function of the bushing. In the rare case that one of these bushings may actually be worn and loose, then a trip to an electric motor shop may be in order to procure the replacement part. These are common spherical bronze bushings with a standard bore size, so they should be available wherever electric motors are serviced.
Oh, and about rewinding that armature? That job was fairly easy as well, and it went so quick that it was done in an hour with about $5 worth of magnet wire, but I forgot to take pictures in the process. Sometime in the near future I hope to do it again (with someone else's heater motor of course) just to get the pictures, at which time I will post that entire procedure here as well. Meanwhile, stay warm and keep 'em rolling.