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MG MGA - Have i killed the batteries?

OK - old chesnut. Hadn't started the car for some weeks - turned it over and the batteries went flat so i reconnected the conditioner. Once fuly charged, i turned the engine over quite merrily, without ignition, to get some oil pressure. Once i had got oil pressure, the batteries were fading and there was not enough oomph to provide a spark etc. No problems think i, simply recharge the batteries and away we go. Now here's the rub - fully charged 13v, ign on, fuel pump clicks up, pull the starter and .... absolutely nothing - ign light goes out and voltage drops to about 7v. Have i deep cycled the batteries and wrecked them? There is no reason (other than shear cold temperature) for the engine to not turn today compared to yesterday - all terminations are clean etc. Lights are fully bright and don't fade, but when i pull the starter everything goes out - could i have a jammed starter (as a a result of it not throwing back once the batteries were flat?) Makes me think about going to a modern 12v set up and possibly even rigging up some external connection just for regular turning over to get oil pressure before i use the onboard batteries to fire up. It's too damn cold to check the starter (six months old)or anything else now.

regards
Colin
C Manley

Sounds like a bad connection, I had exactly the same problem on one of my cars a couple of years ago and on that of a friend last year. The problem in both cases was in one (or more) of the the cable to clamp connections (easily overlooked) rather than clamp to terminal. Everything going out after trying to turn over the engine suggests a bad connection.

That said cold weather will help to kill a battery that is genuinely dying!

As always check the earth connections and try shorting across the starter switch to rule that out as a cause.
Neil McGurk

Read the voltage at the battery terminals (on the actual terminals, not the cable clamps) while you are cranking the starter. If the voltage on the battery terminals is not dropping significantly, then the problem is in the cables or connections (I had corrosion up under the insulation of a set of cables on one car we had that produced the exact same problem). Cheers - Dave
David DuBois

Hi Colin. I would charge the battery and then test each of the cells with a battery tester (hydrometer) THe battery tester will tell you if there is a dead cell or two. If you have a dead cell, the battery needs to be replaced. Cheers and Happy New Year, Glenn
Glenn Hedrich

Hi and happy new year
I had similar problem,turned out, my battery switch did not wonted to be friend of mine and quit.
Martin
m zazvorka

OK. Thanks guys. Have cleaned (they were not dirty)all 4 battery terminations amd graphite greased them plus cleaned the earth connection on the chassis. Have 6.? volts on each battery and 13.? across the two (the ? reflects the fact that it is a needle meter not digital). The starter motor is not jammed and i have 13.? volts from the input side of the starter switch to earth but 0 volts from the output side to earth when the switch is operated. This shows that the starter switch is my problem and cannot handle long term cranking - repro quality? I'll work up a means of providing a shore battery and solenoid supply to turn over the engine to get oil pressure before i use the onboard batteries to start - any suggestions for a suitably rated plug and socket in the UK? Still too damn cold to work in the garage for too long.
regards
Colin
C Manley

The first new starter switch I bought failed after about half a dozen starts. Its similar replacement is OK so far after about a years use. Has yours got a white nylon/plastic base where the terminals are? The one here looks a bit more like the real thing http://www.ahspares.co.uk/products/STARTER-SWITCH-XELS101.aspx or maybe this one http://www.brownandgammons.co.uk/product.aspx?CID=FA7D90FA-A5E3-4200-8EF2-BFE88A81DB74&SID=&PID=ce88307e-d176-4338-8000-784f4fb35658
Lindsay Sampford

Hi Lindsay,
If i recall, i think it did have white nylon, but with black separator shields - it was from Moss, but i can't see properly until i get it off. I recall looking at Barney's web site on the topic of dodgy switches.
I'll call B&G on Monday. Moss & E-bay are cheaper but if the switch is garbage it's not cheap at all. regards
Colin
C Manley

I got mine from eBay (being a bit of a skinflint when it comes to the less glamourous bits and pieces) so it's probably best avoided!
Lindsay Sampford

Lindsay - I too got mine off ebay for about half the price of the B & G one - also lasted a year so far - let's hope it doesn't burn out too quickly!!
Cam Cunningham

This talk on the starter switch caused me to put a voltage meter across the starter terminals with the ignition off. I was expecting it to read zero but it measured 12 volts. I know theres a brown lead from the live side of the switch to terminal A of the regulator but this does not go to earth so I still can't see why I can record a voltage across the switch? My O level physics is a bit rusty but with the switch not pulled surely the circuit is open and therefore there's no voltage flow? Apologies for slight change of subject but I thought this question might have some small relevance.
J H Cole

The coils on the starter motor have a very low resistance and the non switch side of the windings is earthed. The other side of the switch goes to the battery, so what you are measuring is the battery voltage to earth (through the starter motor coils). Your meter will not draw enough current to create a measurable voltage drop across the motor coils.
Malcolm Asquith

More interesting to read the voltage drop across the switch terminals with the switch pulled and the engine cranking (ignition off). Should theoretically be zero. The higher the reading the worse the switch. If it reads twelve volts with the switch pulled, your engine isn't cranking and your switch is bust!
Lindsay Sampford

Thanks malcolm, I got out my old Nelkon, electricity and magnetism and as you say the volt meter is measuring the 'potential difference' across the switch between the battery and earth, not the actual voltage 'flowing'. Its its the ammeter that measures flow. Surprising how much basic physics one needs to understand these old cars let alone new ones.
J H Cole

Colin

I have a couple of used starter switches that I picked up at a boot sale. Both appear serviceable on my meter. They are Feb 1964 and Jul 1966 respectively. You are welcome to one if you wish.

Steve
Steve Gyles

Steve, Are you sure that they are MGA and not MGB? MGA's have a cable-operated manual switch and the "gentle-annies" (like me) pull the knob too gently causing the contacts to arc and burn, ultimately interrupting the current. It is possible to lever them apart and clean the contacts but the "experts" will notice the resultant damage to the switch body unless (like in my cars) the air trunking (leading from just behind the grille) very effectively hides the switch!
Barry Bahnisch

Barry

Lucas Part number76701A. Look MGA to me.

Steve


Steve Gyles

Steve,
Thanks for the offer but i had a spare (in as much as i could rob it from my push rod car). I proved the starter switch on the push rod car, put it on the TC and no starter turn, I put the 'suspect' TC switch on the pushrod car and plenty of starter turn.

Lindsay's explantion shows how i was wrong in diagnosing a duff switch: i got zero volts on cranking, but had no turn from the 'free' Starter. It now seems i might have cooked the Starter Motor (Insulation, windings?) whilst turning over for some time to get oil pressure with the ignition off.
That'll teach me for leaving it so long between start ups. Again, I can rob the pushrod Starter to prove it, but it's too cold to do any more in the garage today - i have only just got feeling back into hands and feet from being out there this morning.

When i thought it was the switch, i was going to knock up a solenoid/battery shore supply and in line connections direct to the Starter so i could turn the engine to get oil proessure without loading the starter switch so much - but if it is the Starter, this will not improve matters.
regards
Colin
C Manley

Steve, Thinking about it after my posting, similar switches were no doubt fitted to cars (?) and commercial vehicles after the discontinuation of the MGA, hence the 1964 and 1966 dates. Come to think of it I have probably picked up later ones at autojumbles (which we call swapmeets).
Barry Bahnisch

Barry

Lucas would have continued manufacturing the part well after MGA production. I have many Lucas replacement parts fitted, post the production period. They were one company that stamped their parts with sensible production dates. It would have also been fitted to many other cars at that time, hence the non-MGA bracket on one of the terminals in my photo. The part number on the one fitted in my car is the same.

Steve
Steve Gyles

This thread was discussed between 01/01/2010 and 05/01/2010

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