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MG MGA - Heater motor

Hi, could someone please advise the correct orientation of the heater motor relative to the main body of the heater. i.e. where the wiring exits. Not sure it matters too much but I would like to get it right.
Very many thanks
Mark
M Dollimore

I have just replaced the motor on my heater Mark, I have fitted the MGB motor which runs a fair bit faster than the old one.
There is plenty of length of cable to reach the bullet connectors on the loom and so it doesn't really matter where you orient the motor.
I chose to fit my motor so that the specification plate can be easily seen by any future owner from behind the heater unit.

There is plenty of space behind the heater unit to tuck any excess cable out of the way.

Colyn
Colyn Firth

Hi Mark

This is how it is on my heater. I am pretty sure this is correct as I was very careful to keep as original when I restored it.
It just happens to be out of the car at the moment.
John


John Francis

This is the uprated MGB motor in my heater, the power cable is pretty much the same position as Johns although it isn't visible pn this picture.
Colyn


Colyn Firth

Many thanks Colin and John.
I have 2 MGB heater motors and both are shorter than the MGA's. Yours Colin looks even longer than the A's hence the increased performance I assume?
M
M Dollimore

Mark,
the Moss replacement for the MGA heater fan motor is pretty much exactly the same dimensions as the original MGA motor, the difference is that the flange on the new motor is 1/3" further onto the motor than the one on the MGA.

The problem is that the flange on the new fan is spot-welded onto the motors body.
Fortunately, the flange on the original MGA fan motor is detachable and so I was able to bolt it onto the new fan in the correct position using longer screws and some spacers.

You can probably see these on the picture I posted earlier, this worked fine and I was able to position the new motor and fan perfectly in the heater body.

The new motor is a permanent magnet motor and runs much quicker than the original motor.
It normally runs in the opposite direction to the MGA motor and so you have to reverse the connections to reverse the rotation direction.

I fitted this along with the upgraded MGB plastic fan and I would say that the airflow output from the heater has been doubled by these mods.

Colyn
Colyn Firth

Colyn Firth wrote:
"The new motor is a permanent magnet motor and runs much quicker than the original motor".

There is a quirk of operation with this new permanent magnet motor. If you have it on and running when you switch off ignition, it acts like a generator on run-down, providing enough voltage and current to keep the ignition coil sparking, so you can have ignition stimulated run-on for a few seconds until the blower speed runs down.

Very annoying at first. It took me a while to get used to switching the blower off before switching off the engine.
barneymg

Well I have to admit that, although I have fitted the new permanent magnet motor and heater fan, I haven't yet driven the car anywhere because of the lockdown.
So I haven't yet experienced the "run-on" effect of the motor.

It looks like you have just discovered a new potential emergency power supply for the MGA Barney, like they have in jet aircraft, in the event of power failure.

We just have figure out a way to use the airflow to keep the fan spinning😀.
Colyn
Colyn Firth

Yes, very interesting. Once you know about this "feature", you can remove the key and hand it to a friend while the engine continues to run more or less normally for a few more seconds before it quits. Try it. Good for a laugh.
barneymg

This thread was discussed between 11/05/2020 and 13/05/2020

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