Morris Minor Owners Club

philthehill wrote: ↑Thu Apr 18, 2019 7:56 am When replacing the dynamo brushes the commutator segments must be parallel not uneven where the brushes have worn them (usually rectified in a lathe) and the commutator segments must be undercut. See BMC wksp man Fig. N5 for details.

Just replacing the bushes is only doing half the job.

Phil, If the commutator had required attention I would have dealt with it. It showed no significant wear so I cleaned it and re-assembled it all. As I've said, this was several years ago and the car has had almost daily use since including long trips abroad, so whilst it may be "half a job" in your opinion, it does appear to have worked fine so far.... Surely this just goes to show how reliable a system the dynamo is
By contrast, the brand new alternator fitted to my daughter's Minor didn't last nearly as many years or miles as my dynamo brushes before another new one was required.

The under cutting of the commutator segments and the segments being parallel is not my opinion but a requirement for the dynamo to work efficiently.

The point being that just stating that the brushes were replaced may lead to a not so knowledgeable person just replacing the brushes without considering any other actions that may be required - which results in the dynamo running inefficiently (or not at all) and they are left wondering why.

This web site is read by a wide audience with a large variance in knowledge and therefore it is imperative that the right and full information is given.

Phil

Surely this just goes to show how reliable a system the dynamo is
By contrast, the brand new alternator fitted to my daughter's Minor didn't last nearly as many years or miles as my dynamo brushes before another new one was required.

I would agree with you on the reliability of dynamos - they were likely well over-engineered. But I would disagree about contrasting dynamos with alternators. Admittedly, like all modern items, they are most certainly not so over-engineered! But solid state regulators don’t often give bother, drive-end bearings likely fail because the belts are cr*ppy resulting in being over tensioned (but a new bearing is peanuts). Rectifiers are more reliable these days (but they will not put up with back emf spikes). I’ve only bought two exchange alternators in 50 years - and one proved unnecessary as it was found to be an intermittent fault in the wiring harness (car had clearly been bent before I bought it - but it was cheap enough).

You only need to look back at the number of failed control box reports, on the forum. I don’t think I have ever changed one, so never come across one made in a shack somewhere in India. I still have one that I think was removed from the Ford Cortina Mk1 when we changed to an alternator

My first alternator on a car was a derated Lucas ACR, previously fitted to a tractor. It was adequate, and far better than the dynamo it replaced - not much extra amperage, but delivered full load at nearly all engine speeds. That one was only replaced because we started using about 1/2kW just on the front lights alone!

I expect many alternators are exchanged because the outside brush needs replacing. A case of ‘replce it, don’t fix it’. I suspect that most “brand new” alternators are likely refurbished, not actually new.

Jenko, returning to your original question (interesting though the above discussion is) as in your other thread we seem to have found that the lights in the speedo are not necessarily correct, is the red light really the ignition light? Although other tests do indicate a dynamo issue, just doubkle check that the red light really is what we expect it to be

Good point. It’s been flickering at low revs for a few weeks.
The car drove back home for 10 miles after it came on fully the first time and no strange noises or smoke from the engine. It doesn’t burn oil or water.
So with this history I have assumed it’s not a low oil pressure light, plus the fact that the checks detailed above show that the dynamo is faulty.
Good point though!

Please don’t assume. Only about 5psi is needed to keep plain bearings apart. Oil pressure warning switches are prone to failure. Simply checked by removing the connection at the pressure switch, costs nothing in time or expense. I still prefer a proper pressure gauge (as well as the “idiot” light) for monitoring important parameters.

I'll need to check the function of the idiot lights anyway. I'm not sure they're set up right. When the ignition is switched on, the red light comes on but no orange.
I understand that there should be an orange light in the right side of the speedo that extinguishes when engine starts.
Both my orange lights illuminate when lights are switched on, which I understand is incorrect for this model.
It's a work in progress but I'm determined to get it set up properly!

It sounds like someone has mixed up the speedo illumination bulbs with the warning light bulbs on the back of the speedo.
My 69 Traveller has a spare orange warning light on the LHS, the other orange one on the RHS is for the oil pressure.

I am considering wiring a hidden fuel pump cut off switch as an anti theft device, my plan is to use a double pole switch and use the second pair of contacts to switch the spare orange warning light on when the ignition is on and the fuel pump is off, that way I have a visual warning that I need to remember to switch the pump on before I set off. I dont suppose a thief would know what that light meant though.

Phil

pgp001 wrote: ↑Fri Apr 19, 2019 3:43 pm I dont suppose a thief would know what that light meant though.

He does now

I fitted a 'secret' switch for the fuel pump and the first time I went out afterwards I switched it off and left the car. Came back to it and drove off - then wondered why it spluttered to a halt 100 yards or so down the road. Then I remembered the switch! Getting used to it now...

Absolutely ***%^#^#^^~~ brilliant. Connected the new Dynamo, started the engine, red light went out after a couple seconds, not even a flicker.
Solved! Thought I, happy days.
Nope.
Smell of burning, looked back under the bonnet and smoke coming off the dynamo. It had only run for about fifteen seconds. Red hot.
Quickly switched off, disconnected the battery, then the dynamo connections, which were hot.
Any ideas?.....?
It was a brand new Dynamo. Connections were in a slightly different place, but same sizes.

If there are any enthusiasts in the North Shropshire area, I'll happily pay someone to sort this.

Get an alternator

One thought, it is possible the cutout is stuck and the battery is trying to run your new dynamo as a motor and overheating it and the cables.
To get that hot, there must be a large current flowing one way or another.
I would try and borrow a known good control box of someone to test it again, and eliminate that as being the problem.

You can look at how to test and adjust it in the manual.
http://www.dolphnproductions.com/morrisminor.pdf

Phil

I’ve sent you a PM

If it was trying to run it as a motor, would I hear some sort of noise when I connected it?
When I tried the motor test with the old Dynamo, as soon as the contact closed, it spun.
The contact is now closed, where it wasn't before.
If I knew someone who had a spar control box, I would.
Unfortunately I don't know anyone else with a moggie, hence using the forum.

Where exactly are you ??

Thanks for reply to my PM. I’m between Bridgnorth and Ludlow. Unfortunately I have a heavy schedule over the holiday but if you are still in trouble first week May I could come up . I have no particular expertise but I have a manual ( BMC Workshop ) , meter and an extra head may help.

That will be a big help.
I'm also working over the BH but if I haven't got it sorted, and I don't see what else I can do now, I'll PM you for beginning May.
Thanks.

I do not think that PGP100 was being off hand in his comment but being realistic.

The fitting of an alternator mod kit is so easy and as regards the wiring alterations it is described in detail on this web site.

Whilst anything can be unreliable I have never had any problems with alternators on the various cars I have owned.
Checking the condition of the brushes at a high mileage is an imperative.
It has to be remembered that an alternator turns at nearly twice the speed of a dynamo so will have turned many more revs for the same mileage as a dynamo.

Fitting the alternator gets rid of any control box issues.