I checked Vic Brit's catalogs on the MGA and MGB. I have a MGA catalog from
Moss but not one for for the MGB so I checked their on line catalog. Here's
what I found.
1) The MGB went from a generator to an alternator in 1968 at chassis 138401 for
the roadster and switched to negative ground.
2) Vic Brit lists the same heater motor for the MGA and MGB, Moss doesn't. Moss
changes stock number for the MGB at chassis 138401 for the later cars, Vic Brit
doesn't.
Vic Brit is also selling the same heater motor for the twin cam. I have a twin
cam
which uses a heater housing that is a mirror image for those in the standard
cars. That is, everything is switched arround with the air trunking on the left
side rather than the right. The motor only runs one way regardless of
polarity. That is why the heater motor
for the twin cam has a different BMC part number than the one for the standard
MGA. I have a NEW standard MGA heater motor and it runs the opposite direction
of the twin cam's regardless of the polarity.
3) Vic Brit lists the same rebuilt wiper motor for the MGA and MK I MGB. Moss
lists two different motors. According to the illustrations from both sources
and stock numbers, the wiper motor for the MGB changed design at chassis
138401. From the illustrations, the
early MGBs used a wiper motor that looks the same as that used in the MGA. This
motor isn't round but is rectangular. The rectangular wiper MOTOR on my twin
cam rotates only one
direction regardles of polarity. It doesn't have permanent magnets, but is a
series wound motor just like the heater motor for the MGA.
MY conclusions:
1) Vic Brit is selling the later MGB heater motor as a replacement for ALL MGAs
and MGBs as it will run either way by switching the leads. Moss is selling the
correct item for each different model.
2) Early MGBs, MK I, with the generator and positive ground use heater and wiper
motors which are NOT polarity sensative.
Blake
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