MGB MGB 5 wire to 3 wire alternator

[aeronca65t]

Wednesday, I drove my MGB into work.
As I pulled into the staff parking lot, I heard a "SKREEEECH" and then the charge light went on.
And I could smell burning rubber.

It's been making a funny, clicky sound in the front for a while so I figured the alternator or water pump was on the way out.
Turned out to be the alternator. Front bearing was frozen solid.

So I coasted into a parking space.
After work, I took out a 1/2" and 9/16" wrench and loosened the belt just a bit. And sprayed the belt with silicon spray to encourage slipping (doesn't everyone carry stuff like this in their trunk?).
And drove it home (just 3 miles and with engine off when I could coast).

I found three old alternators in my junk box.
One I knew was bad electrically (but turned OK), one with an "ear" broken off and one that looked terrible. I had no idea of the condition of the second two.
The MGB (a '69) has the old style 5-wire alternator, which is no longer available.
The alternators in my junk box were all 3-wire Lucas jobs (probably all from Midgets).

So I took apart the 5 wire and one of the 3 wire units and put the front half of the 3 wire on the 5 wire unit (so I could keep the wiring as-is).
Worked, but poorly....charged at about 1200 rpm and then kicked out (light on) at about 2000 rpm.

So I took one of the unknown 3-wire jobs, made up an adapter cable (as per instructions from Moss Motors) and tried it. No go.
Then I took two of the 3-wire jobs apart and tried to make the best of those. Again, no go.
So I took part of the electrics from the last 3-wire and put it in to a unit that was now cobbled up from all three of my 3-wire units.
Installed it in my 5-wire MGB with my home brew adapter and.....success!
Drove it to work yesterday.

I love it when a plan comes together!

5-wire to 3-wire alternator conversion from Moss

 

[drooartz]

Well done, Nial. Handy to have lots of spare parts around -- and nice that the Midget and MGB bits can be adapted for each other.

 

[PAUL161]

Not necessarily on your car Nial, but most alternators sold by various auto stores today have chinese bearings in them. The original Delco alt on my truck lasted for 150,000 miles, since then I've had 4 rebuilt ones on it as the front and rear bearings come unglued. Talking to a guy at O'Reillys, he said just about all returns are because of bad bearings. The chinese don't grease them properly during the manufacturing process. I actually carry a spare new alt in my truck tool box. I hate being stranded.
I had a starter/generator repair shop rebuild the original one on the B for 60 bucks. Believe it or not, some of the internals and bearings are still available. PJ