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MG MGA - Electrics problem - where to look?

Hi, would really appreciate some help where to start looking on this one. I was driving the car about four weeks back, and having been out for about half an hour (i.e. engine nice and warm), I stalled when I stopped at a corner. Problem is when I tried to restart, the starter motor wouldn't turn and it seemed like I had a flat battery (I tried several times but it wouldn't turn over).
Having left it alone for 10 minutes, it then turned the engine over easily and started first time.
I assumed it to be a flat battery but have not had a chance to spend time with the car over the last few weeks. I tried to start it today expecting to find the battery was flat but it turned over just fine. In fact as it was very cold, I had to try 6 or 7 times before the engine fired, but the battery did not complain at all.
So it looks like the battery is OK. I have checked for loose connections in all the obvious places, without success. So am not really sure what to try next.
In case it's a clue, my engine (when warm)idles at about 1100rpm so I am not sure why it would have stalled in the first place.
Many thanks, Graham
Graham M V

Graham
Could be a jammed starter pinion?
Try rocking the car in gear to free it
Paul
P D Camp

Graham, bad connections are not necessarily loose connections! Try the battery lead where it connects to the chassis for a start. Unbolt it from the chassis, clean up the chassis to bright metal and also make sure the terminal lug is in good electrical contact with the battery lead, not just mechanically connected; I soldered mine to be sure. Reconnect the lead with a nice new bolt and put a good dollop of petrolem jelly on it. The other old favorite is the earth strap that bridges the left hand engine mounting, again, make sure everything is in good electrical contact, in fact it is more likely the engine earth that caused your trouble if the engine cut-out. See if that helps.
Lindsay Sampford

Graham, don't stop there. I had loads of minor starting and charging problems until I went through every connection from lead to clamp and clamp to terminal on the batteries (or battery). None were loose but they all needed "improving"! Admittedly, this is more common on twin six volt batteries, but well worth a check before you strip or replace your starter.

Neil
Neil McGurk

Thanks - Hadn't thought about it but Lindsay is right of course, a firm connection is not necessarily electricaly sound. Neil - I do have twin six volt batteries, do some "upgrade" to a single 12 volt?
Anyway will do as you both suggest and reconnect all the terminals. Am I right in thinking it can only be a battery terminal (or linkage), the engine block earth strap, or on the starter motor? If so, that's quite straightforward.
(Paul, the starter didn't jam, it just struggled to turn with any speed)
Thanks, Graham
Graham M V

First, be sure all the grounds and power connections are clean and tight as recommended above.

I had a very similar starter problem with a fairly newly rebuilt starter. After pulling the starter and getting it checked if found it was just a sticking brush in the starter. The brush would stick and not make contact at random times (always the worst times).

The brush holders were cleaned and the brushes lightly filed on the sides and hopefully the problem is solved.

Seems that some of the current replacement brushes may be slightly oversize from the originals.

Jim Ferguson

The only way to see if connections are clean is to look between the surfaces. "tight" connections can be poor. Sounds like dirty battery connections. I use 1 12 volt battery. Fewer places for bad connections and a less expensive and more powerful battery. Unless the originality of the six volts is important to you there is no need to retain them.
R J Brown

All the above advice is good. Your "flat battery" could be the symptom of a bad starter switch. Did you check your headlights to see if there was any power?

Ahhh... I see later you described it as "struggling to turn with any speed" Very typical of a dirty or loose electrical connection. After you check all the heavy current connections, It could still be dirty contacts inside the starter switch. IF everything else checks out, it could be worn brushes and/or springs in the starter. Check the voltage available at the starter switch terminal to the starter while trying to crank. IF good, I would expect to see around 11-12 volts if the starter switch (and incidentally all the wiring from the battery up to the switch) and battery are good. If you place the ground lead of the voltmeter to the body sheet metal and not the engine, you are checking the engine mount wire at the same time.

About 20 years ago on my DD, I had a problem similar where the bad connection was internal to the battery. Most of the time it would start just fine, with no lack of energy. Other times there was NOTHING. No lights radio or anything. Replacing the battery fixed that problem.

Again a similar thing happened to me last month on my current DD. This time the car wouldn't start. My wife had someone jump the car and nothing happened. Then she called for road service and they jumped the car just fine. On the way home, the car died instantly with NO electrical power. Turned out the terminal on the battery broke off internally. It was only making casual contact.

A single 12v battery is definitely an upgrade. THere are fewer HIGH CURRENT connections required. Especially if you use the generic replacement battery terminals that clamp on the wire.

To reduce any ongoing corrosion at the battery terminals, I swear by the red and green felt pads that sit under the connection. I use them all the time.

Good luck in your investigation.

Chuck Schaefer

Hi,
The problem is that the fault is intermittent and the starter turns over just fine at present, so there is nothing to test with the meter. Ideally I would want it to misbehave in my garage but I am sure it will wait until I am a long way from home, it's pouring down and I am running late!
So I guess for the time being I will just check the major connections. I think Lindsay made a good point that it may well be the earth strap on the block, as it was very strange that it cut out for no apparent reason.

I am interested in replacing the 6 volts batteries with a 12v when they start to play up. Where is the best place to site it?
Graham M V

Since last post have checked out the archives regarding 12 volt batteries and found all the info on exchanging 2 x 6v for 12v. Sorry, as should have done so first.
Graham M V

Hi Graham, I have recently replaced my 12v battery. I used one meant for a Fiat Punto diesel van. It fits into one of the 6v cradles. I got mine from Halfords but it was rather expensive at 80!( I didn't have time to shop around) - cheers Cam
Cam Cunningham

Hi Graham, if it is intermittant it is quite likely to be the earth strap on the engine. The shaking about of the engine is going to make the fault come and go. Without a good electrical bridge across the rubber engine mount, the block will have to find its earth via the control cables, the temperature gauge pipe or the metal braid on the carb fuel lines via the float bowl overflow pipes if they are attached to the block (can't think of any other block to chassis metalic connections but no doubt someone will come up with one or two more!). These are not going to be a good path for the high starting current and may even cause trouble for your ignition (cutting out) and generator circuits. I think I'd go there first. Lindsay.
Lindsay Sampford

Graham,
I had exactly the same problem only a week ago. When I got back to my garage I discovered a loose connection of the thick cable running from the starter motor to the starter pull switch. This switch is mounted directly under the 4" heater ducting pipe in the engine bay, and unless you poke your head right inside the engine you will not be able to see it. The nut holding the cable was loose with the obvious result. Tightened the nut and all is working fine.

Frank
f camilleri

This thread was discussed between 27/11/2009 and 29/11/2009

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