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MG MGA - Starter woes

Just returned from a three week European tour with no problems with my car apart from a little plug fouling in a very hot Monaco.

Now my starter motor is making my head scratch.
Firstly, the battery is fully charged and the connections through to the starter switch seem ok. The motor will engage the ring gear but won't turn the engine more than a tiny bit and stalls. With the headlights on they dim to nothing which suggests a dead short somewhere.

On Barney's site I noted the possibility of a failure of the insulated post with the main connection shorting to the end cap. I removed the starter and checked the insulated post for the main connection. It was a little loose so have reassembled it carefully and tightened it. There was no short to earth when tested with a meter with the brushes fitted.

I did check the resistance of the field coils to earth which was about 0.5 Ohm. I can't find a reference to what that should be but maybe that is a problem? However on the bench with a spare battery it all runs fine albeit with no load.

Back on the car and the problem is still there. Any ideas?

John
John Francis

High resistance through the horrible starter switch. A lot of current goes through that thing and arcing becomes an issue. See what I found when I pulled one apart.

You can try twisting the puller shaft round a bit to see if you can bring a different part of the contact brass disc into contact.

Steve

Steve Gyles

Hi Steve
I did wonder at that but why would that pull the volts down for the headlamps? Its a new switch only two months old. I'll try the old refurbished one. PS I took the starter out again and the field coils have OL resistance to earth with the brushes pulled out. So the field coils are OK.
John Francis

John

Don't ask me technical questions on electrics! I will let others answer that. That starter switch was the prime reason I went to a pre engaged hi torque starter. That way the switch takes only a very light load to the starter solenoid. The main load to the starter motor by-passes it. prior to that I had all those starting issues not dissimilar to what you describe. Since switching over I have never had an issue.

Steve
Steve Gyles

Dead battery---? or dirty battery connections
Worth a try with a jumper battery
William Revit

Well after a lot of faffing around I eventually checked the voltage at the battery on cranking. It dropped to 5V so no wonder it wouldn't turn over. My battery charger, which is of the type that you can leave connected all the time, indicated that the battery was fully charged. I now don't believe that!

I added an old jumper battery which helped a bit but not enough so after starting the car on the handle, which was harder than I expected, and running for a few minutes to charge the battery, I can now start it with the starter. What a lot of wasted effort, new oil filter etc!

I now have to figure out why the battery went flat. I have a master cut off switch and the only things permanently connected are the clock and the tracker which both draw very small currents. It could of course be that the battery is at the end of its life approx 10 years.

Thanks William for reinforcing the dead battery check and using a jumper battery.

John Francis

10 years on a battery is good going - most of mine only manage 5 or 6.
Cam Cunningham

Your battery is suffering either a sulfated condition where the lead sulfate crystalizes or there is a bad cell in the battery; either can lead to loss of cranking power and inability to hold a charge. In a new battery it can be brought on by a manufacturing defect; in a 10 year old battery its just part of the battery life cycle.

Nick Kopernik

John

Glad you found the issue. Changed mine 4 months ago after 12 years. Made a difference.

i know it's not original, but the pre-engaged starter is an interesting option: http://www.mgaroadster.co.uk/hi_torque_starter_motor.htm

The only drawbacks, other than originality, are cost and another oil filter. The +vs are many: hardly any draw through the crappy starter switch; no gnashing of teeth (starter motor only turns when fully engaged in starter ring; if the starter ring is worn on the 'conventional' side this is a good option as it uses the forward facing side of the starter ring.

Every starter issue I ever had with an MGA disappeared when I went this route. Just like a modern car.

Steve
Steve Gyles

Coincidentally, I fitted a new Varta battery to my motorbike in April. I tried to start it yesterday, but it wouldn’t turn over - voltage dropping to 7v when trying.

Still waiting for a response from the supplier!
Dave O'Neill 2

One point related to the pre engaged starter option I presume they are polarity sensitive? If so is positive earth version available? Also I have never heard of standard staters being polarity sensitive as any DC electric motor will go backwards on opposite polarity?

Paul
Paul Dean

Paul

Presumably, as you are reversing the polarity of both the armature coil and the field coil, the motor will continue to turn in the same direction.
Dave O'Neill 2

My car is Pos earth & I didn’t do any reverse wiring when I fitted a high torque starter. Works fine.

Regards
Colin
Colin Manley

Starters are ignorant little beasties and do not understand polarity. They just go on ahead doing their thing until they get sick.A little doctoring is then required.
Sandy
Sanders

A couple of learning points from this.

I recently fitted a battery isolator on the earth side. When I connected my trickle charger under the bonnet I forgot that the isolator was off so it wasn't charging the battery. However, the charger indicated the battery was fully charged so that confused me when fault finding.

I replaced the battery and took the old one to my local scrap dealer who gave me £5.88 for it as scrap which was pleasing. So the nett cost of the new one was only £47. I fitted a Varta B36 44AmpH.

I was surprised that there was no warning of the battery failure. We had just been on a tour of Europe for 3 weeks with no sign of any problems.
John Francis

This thread was discussed between 16/07/2018 and 29/07/2018

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