MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Battery probs?

Hi

Im on the second day of "proper" MG ownership and it already feels like Ive never been away.

I bought a 1971 BGT yesterday, had a lovely 400ish mile round trip to collect it. It ran beautifully on the way back, sitting at a steady 75mph on the motorway (I was impressed with the overdrive - Ive only had a 1275 midget before). The car isn't the prettiest looking car, but it is all solid underneath & sills etc. So I was in a good mood.

However, Ive noticed a petrol leak from rubber pipe near where the metal pipe comes out of the tank, (no probs there as I've got plenty of that pipe and jubilee clips)

Main question though, the car has had one new 6volt battery recently. Ive noticed today that it can be reluctant to start, it doesnt do anything sometimes when the key is turned and sometimes you can hear the solenoid clicking, but it usually will turn over and catch into life. The indicators also dont flash, they just stay on and the headlights are very dim. The red ignition light also comes on during tick over. Could these all be related and be due to the other 6volt battery being on its way out?

Second question, the passenger door fits ok, but the door glass is miles away from the door seal, can the glass be adjusted inwards?

Cheers
John

PS, I do love driving it, I went out earlier and did over 40 miles for no reason other than I wanted to. I love the exhaust note!
J M Collins

You may get very specific answers by those who know much more (let's hope for your sake) but the first thing I'd do is convert to a twelve volt (group 26?) battery. Muy easy and much in the archives, I'm sure. Dimming lights and slow flashers may be that the charging system is on the fritz and should have alternator investigated/tested.

If not anything else, test specific gravity of your batteries and perhaps trickle charge till full charge is obtained. Have the batteries load tested at a shop with proper equipment. Clean battery posts and check all connections, including both ends of ground wire.

Paul
Paul Hanley

One new 6v battery is not a good idea, they are usually best replaced in pairs if they are simply time expired, although replacing just one can be OK in the event of physical damage or a sudden failure of a fairly new battery. I've never had a problem with twin 6v on the roadster that I haven't also had with single 12v on the V8 GT, so I wouldn't be in any mad hurry to change.

*Sometimes* doing nothing or chattering/clicking from the solenoid indicates intermittently bad connections. Consistently slow cranking (again it depends what you compare it with) could also be bad connections, weak batteries, or weak charging.

Unless the tick-over speed drops below about 600 rpm then the warning light shouldn't come on at idle, once it has been revved to at least 1000 rpm to turn it off. That, dim headlights, and non flashing flashers all point to low system voltage, which could be due to multifarious bad connections as well as a weak alternator. But good MGB headlights are nowhere near as bright as those on a modern car, so it depends what you are comparing it with. The flashers hould falsh at idle, although slightly slower than at higher revs, and they will also slow a bit more when you apply the brakes.

Before replacing anything I'd check the charging voltage. This should be about 14.5v on the brown at the fusebox with the engine running at a fast idle on minimal electrical load. It will probably be less at idle, and as things like headlights, stop lights etc are switched on it will also drop, even at a fast idle, but not below 13v. I'd also check the voltage on the brown at the alternator as well as at the fusebox and directly on the battery posts under the same conditions, you should only get a couple of tenths variation between them, more indicates bad connections. Lower than the indicated voltages on the brown at the alternator indicates a bad alt.

Get the charging right first, then you can move onto the cranking, then headlights and flashers.
Paul Hunt

I would agree that first you should clean your battery terminals. It can take 100amps to crank a cold engine and you can see a fraction of a Ohm will drop quite a few volts. Then stick a charger across the two batteries overnight. They should hold about 6.5v each. It does sound as though you might have a duff alternator if the red light does not go off straight away. It could be the brushes. I dont see any reason to depart from the twin 6v batteries. I had one go down last year and I changed just the one on my 71 roadster. Still seems to be Ok although I did have to put the charger on it after about 1 month without running over the winter. The 6v batteries are about £35 each.
Paul Hollingworth

Hi

Thanks for all the replies,
I've got to wait until the weekend before I can have a good look as I dont have a garage yet, (still waiting for plans to be drawn up & approved).

The car started fine today, In fact it only seems to be when its warm that it doesnt start or that I hear clicking sound?

The red light is only on when the tickover drops really low, and when I have lights on (although I may not see it in the daylight?)

Ive got a digital multimeter, but dont really know how to work it, can I use this to check alternator output?
J M Collins

On the V8 at least hot starting problems like a chattering solenoid are a sign the starter is on the way out.

A digital meter should be OK in normal circumstances, but if you have a problem with output and the voltage is fluctuating rapidly it may not 'settle' and give a usable reading but jump about all over the place. You will never know until you try it. I use both digital and analogue meters for this reason. Whilst a digital will give very precise readings to two decimal places in most cases we just don't need that and most won't give a steady reading on a varying signal. Whereas an analogue should give you one decimal place and give a steady reading on a varying signal.
Paul Hunt

JM,

I completely agree with Paul Hunt about the two six volts swap once versus twice . And I confirm too the same feeling while usind digital and analog multimeters,
the analog one gives a more "sensitive" understanding of the problem. And lastly, a good alternator should supply between 13 to 14,5 volts to compare against the 12V batteries when engine is switched off.
-regards-
Renou

JM,

The best practice to properly check batteries consist of verifying the voltage level while draining them through a power resistor : ie, a 20-30A load should not make fluctuate voltage
- Regards -
Renou

This thread was discussed between 14/03/2004 and 19/03/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.