Here is a great little article from Merv Williams on fitting a Mini heater to a Minor, the Mini's heater being more efficient.
I bought a complete heater assembly from the scrapyard from a 1979 Mini for ten pounds. The heater unit has to be removed from the car to allow access to the radiator, and this is achieved by:
1. Lowering the parcel shelf out of the way by removing the front mounting screws
2. Unscrew and remove the cowls that take the hot air through the parcel shelf. Remove the pipes that take the air to the screen, the tubes may be tight, but they twist off. This allows easy access to:
3. Air intake tube. Unscrew clip and remove.
4. Water connections. Remove the clips and remove, but remember to put a margarine tub or similar underneath to catch the water!
5. Undo the two Phillips screws near the speedo light switch, the two 'L' shaped brackets at the bulkhead. Disconnect the two wires and remove the heater. (NB: Removal of the nearside glovebox helps access, particularly to the nuts on the rear of the Phillips screws).
6. The radiator can then be removed by simply removing the sideplate which is fixed by Phillips screws.
On examination, my original matrix was very choked up. The Mini matrix is slightly smaller, but has a few more fins, so should be more efficient. However, the water connections are in different positions and could not be swapped without modifying the heater case.
The Mini fan has two veins compared to the one vein of the Minor, and the second vein recirculates air from the interior. After having the radiator checked and flushed by my local radiator specialist, (cost two pounds in their charity box), I decided to use the complete Mini heater unit, by making a few modifications. These are:
1. Drill a 15mm die hole to take the fan switch (take measurements from the old Minor casing).
2. Drill a 10.5mm hole and insert a grommet to take switch wires (same position as old Minor heater).
3. From the discarded Mini switch plate, cut a 1" strip of metal, and extend the mounting flange so that it matches the old Minor heater.
4. The original Minor switchplate and flap can simply be slid out of the Minor heater and is replaced into the new assembly.
Replacing the heater is a straight reversal of the removal procedure. But while it is out, make the most of the opportunity to do those little jobs like putting in extra insulation etc.
The replacement heater is identical in appearance to the original Minor one apart from the extra air intake, which is out of normal view. Those enthusiastic about originality may not consider this a worthwhile sacrifice.
My test drive was on one of the coldest days of the winter so far, and I found a reasonable increase in heat output, (bearing in mind my original heater was choked up anyway!), but don't expect searing heat as with modem car heater systems.
There is an increase in airflow with the extra vein, which was noticeable. I felt that this has been very worthwhile, for very little cost, (twelve pounds).
Taken from the new MMOC Technical Manual.
Advice is given by the MMOC in good faith. The Club and its officials can in no way be held responsible for advice given.