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MG MGB Technical - Dodgy starter or dodgy batteries?

This is my first winter with the B... and it's been interesting.

I'm a self-confessed technical numpty... I love cars... I've just never bothered to see how they work before (until now...) so please forgive my ignorance if I say something particularly dense!

Thanks to a dodgy coil at the beginning of December - I managed to flatten the batteries somewhat by turning the engine over for a bit too long... got the coil sorted out and got her going with a booster pack. Took the B out for a couple of hours to top the batteries back up and the next time I went to start her (about a week later) she was very reluctant and turned over very slowly - again the booster pack helped to turn her over.

A couple of weeks ago I invested in a battery charger (with a built-in tester) as I thought that the batteries were probably in need of a good charge... connected the charger up to them and it said that they were fine - 100% charged... it had a trickle-charge function so I left it on for 4 hours or so for good measure. Tried turning the B over and again... very stubborn and slow to turn over (yet again the booster pack did it's job).

I'm a bit confused now... is it that the batteries are shagged? They were brand-new in the summer... so I'm quite surprised - or could it be a dodgy starter? It looks pretty old and I hear that the high torque units are much better anyway.

The thing that puzzles me though is why will the car turn over better and fire up with a booster pack attached to the batteries... can a failing starter draw more power?

Any suggestions/advice very welcome!

Cheers,

Ant
A Kittle

Ant,

It sounds like you still have the double battery pack. That means you have twice the chance to have dirty connnections. Either way, single or double, you need to clean the battery posts and the terminals that connect to the posts.

While the batts are disconnected, remove and clean the cable and terminal where it connects to the starter. Dont twist the stud out when you disconnect it.

If any of your battery terminals (wire ends) are the bolt on type, you need to take them apart and clean those connections as well.

You need to clean wherever the battery ground lines connect to the body. Then clean both ends of the ground strap and its attach points for the line between the engine and body near the engine mount.

If you get all done, and the batteries are up, then maybe it's the starter.

It is possible that a jump pack will start it even when the existing batts are good because it connects to the terminals and not the posts of the batteries.

Charley
C R Huff

Ant. What Charley said, and more and better also. (A reference to Sir Winston on the Arthurian Legend.)

What you describe "cannot happen", but it has.Thus, the focus on what actually exists versus what is actually happening.

Automobiles, really, need to be run on a regular basis. Once a week, for several tens of miles is a minimum. A hundred miles per week is a good, minimum average of what a car needs to be kept in good running order.

The basis of anything electrical, is good, solid contact. All of the contacts at the battery terminals must be perfectly clean. Dousing them with a solution of baking soda (Sodium bicarbonate) to clean them properly is a good idea. Then, follow up with a good circular wire brush on the cable terminals and a good wire brushing of the battery terminals. After that, reassemble the system with some axle grease on the terminals to cut down on corrosion.

There are two types of cable ends. One is a molded on lead terminal. The second is a lead terminal that has a grove and a steel strap across it, held in place by two bolts, and the stripped end of the cable is clamped in place onto the terminal. The former case is the better of the two. In the latter case, corrosion can build up between the terminal and the wires and cause problems. Cleaning with baking soda and a wire brush can restore proper load bearing capability. Better, however, to replace with a new cable having a soldered on connection (or cast on as the case may be).

Put a volt meter across the battery terminals and see what it reads. Should be 12.5 to 13.0 volts for a fully charged battery/series of batteries. Turn the ignition switch to the start position and see what the battery (ies) are reading. If the reading, on the terminals, not the clamps, is reading 11.5 volts or less, there is a problem with the batteries. They may either not be fully charged, or, they might be bad. Again, the quality of the connections makes a difference here. I the connections are not good, the battery (ies) will not fully charge.

More information would allow us to offer more help.

Les
Les Bengtson

Thanks very much Charley and Les!

I need to go and get myself a multimeter... (the toolbox is gradually getting bigger and bigger!).

Yep - it's a 74 BGT with twin 6v.

The battery terminals are bolt-on type and I did notice a bit of corosion when I removed the batteries to charge them - I'll give them a proper clean up.

As for getting to the starter - what's the best way? is it just a case of removing the distributor? or does the oil filter need to come out as well?

Something else I forgot to mention... once the car has been out for a run (say for 40 or 50 miles) and I go to restart it after an hour, it'll fire up without any problem at all.

I really appreciate your help - thanks again!

Ant
A Kittle

Les - when you say to turn the key to the start position to take a reading from the battery - do you mean so that the ignition is on or so that the starter is actually turning over?

Cheers,

Ant
A Kittle

the easy restart when warm is a clue, at this time the batteroies are fully charged so it points to them being near end of life. However I would still do the clean up and then grease already suggested, and buy an intelligent trickle charger (see archives)
Stan Best

Ant. Yes, turning the key to the start position puts a load on the batteries. If one, or both, of them is bad you will see about 12.5 volts without load and significantly less under load. If you see very little voltage drop--11.5V or higher, run a jumper wire from the large terminal of the starter and repeat the check with the volt meter hooked up to the jumper wire and a good ground. If the voltage drops at the starter, but was good at the batteries, the line running from the battery to the starter is the problem. I have seen a bad cable three times--twice with internal corrosion and once with one of the battery terminal clamps which connect to the cable with a strap and two bolts. In the latter case, corrosion between the bare cable end and the clamp would not allow the current to flow through the cable when under a heavy load.

As to the starter, I loosen the top bolt, remove the lower bolt, then remove the upper bolt. Be aware that the two bolts are of different lengths and have different threads. Mark them when you take them out. I remove the starter, and reinstall it, from the underside of the car. Use jackstands under the front spring pans and don't forget to disconnect the battery ground before starting to remove the starter.

Easier starting when warm can indicate either a bad battery, bad starter, or bad cables/connections.

Clean everything throughly, perform the tests, and you should have a better idea of what the problem is.

Les
Les Bengtson

Cheers chaps,

Right - I'll pop out this afternoon and buy a multimeter and a wire brush and I'll let you know how I get on.

Stan - would love to get a trickle-charger but unfortunately my garage doesn't have any power and is 800 yards from my house! Makes things a bit tricky at times... hey-ho!

Cheers,

Ant
A Kittle

If you connected the booster pack to the battery connectors and got good cranking that implies the connections from there to the engine are fine, which just leaves the connections to the battery posts including the link cable, and the batteries themselves. If the batteries wouldn't start the engine immediately after being on charge for 4 hours, that also implies the battery post connections.

To check the connections connect the meter +ve to the +ve battery post (not the connector) and the meter -ve to the battery cable stud on the solenoid. Crank the engine with the coil disconnected and note the meter reading. Then do the same from the -ve battery post to the starter body. For twin 6v batteries do the same on the battery posts that carry the link cable, meter +ve to the -ve post of the '+ve' battery and meter -ve to the +ve post of the -ve battery.

Ideally you will only see 2 or 3 tenths of a volt displayed, which is the voltages lost in the connections end to end. If you see more than 1v it is worth cleaning the connections, I have seen up to 3v lost.

With the meter across the battery +ve and -ve measure the voltage while cranking. With good batteries it should only drop to about 10v, much lower than this shows knacked batteries or low charge. With bad connections it can actually be higher than this, as there is less load on the battery itself, even though the starter is cranking slower. But remember if there are problems in the engine or starter making the engine harder to turn over you can easily see lower voltage in a good battery, it is a bit of a chicken and egg situation.

Paul Hunt 2

Thanks Paul... (great site by the way!)

I'll have to rope someone in to giving me a hand with this at the weekend. I've bought myself a multimeter now so I just need some dry weather and enthusiasm!

Cheers,

Ant
A Kittle

Impatience has got the better of me and there is just about enough light just now to check the voltage across the main terminals and it measures at about 12.25v. One battery on it's own measured 6.25 and the other was 6v.
Also - I measured the voltage during cranking and it dropped to 4-ish volts... that seems very low... but does it indicate one or more duff batteries? That's what I'm thinking from everyone's (very helpful!) replies so far.

At the weekend I'll make a start on checking all the terminals...
A Kittle

Ant,

As long as you are getting impatient, go clean all the connections at the battery. Previously I tried to outline the cleaning of all connections, but odds are itís the ones at the batteries that are causing the problem.

Like Paul said, since the jumper pack works, itís most likely the connections at the batteries. It is the same thing I was trying to say about why the jumper pack would start it even if the batteries are good. The battery acid tends to make those connections corrode more quickly than the other connections.

Keep in mind that the same corrosion that keeps the batteries from starting the engine will hinder the charging, be it from the car or from the battery charger.

Charley
C R Huff

As Les mentioned, moulded on connectors on your battery cables are preferable to the aftermarket replacement clamps he describes for resisting corrosion.

However, in my experience, even moulded connectors on the cables can have serious problems with corrosion ~ just not as often. If battery acid has gotten into actual wire cable inside of the moulded connector and under the vinyl insulating jacket on the cable, the copper strands can also rot and that rot can remain concealed for a very long time, doing fairly extensive damage to the overall battery cable connection.

An example from my own experience is finding that in one such case that once the vinyl insulation was stripped away at the moulded connector, there were actually only 3 strands of the copper conductor that still had any real integrity, the rest of the bundle having turned to a mass of corroded and separated copper. The obvious culprit was battery acid which, over time, had entered via a less than perfect seal at the connector/cable connection.

Three strands is not much to carry the load of a starter or some of the other high current draw items (fan motors, rear window defoggers, headlamps, etc) and greatly affects performance of them. Check your cables carefully as they are not a lifetime item and at the age of our cars, stand a better than average probability of needing replacement.
Bob Muenchausen

In my experience the moulded cup-type connectors are terrible as they distort with repeated removal and replacement and eventually can't be tighted properly. This is when POs stuff silver paper in them to try to pack them out again. They are also only secured with a pretty puny screw. The later bolt-up clamps are miles better, even though they have to be secured to the cables with bolts instead of being moulded on. Liberally smearing the connector and post, before fitting together, with Vaseline keeps corrosion at bay. And never use those accursed so-called 'battery bins', they make corrosion much worse as the ventilation is mucch more restricted. They are really only for use in the battery cradle made spare when converting from twin 6v to single 12v. Which I wouldn't bother doing either.
Paul Hunt 2

I've just had a very fun afternoon cleaning up all the terminals. The batteries have been on trickle charge for most of the day too.

There was quite a bit of corosion where the earth lead fits to the body and the posts and connectors were all rather gungy... a bit of elbow-grease with a mini wire brush and some light sandpaper and all is nice and clean again.

Put everything back as it should be (with lashings of vaseline!) and after a bit of hesitation - the B lives!

Cheers for all the good advice... very much appreciated.

I think a new alternator is in order though - when she's idling there's only 13.4v across the battery posts - should be more like 14 - 15v shouldn't it?

Cheers again... I'm off out!

Ant
A Kittle

13.4v is a little low at idle, but it depends how much electrical stuff is on. If it rises to 14.5v at 2000 rpm, and stays above 12.8v at 2000 rpm with everything switched on, it will be fine. Measure it at the alternator terminals as well as the battery posts. Any difference of 0.1v or more shows you have other bad conenctions elsewhere.
Paul Hunt 2

Thanks Paul - I didn't think to check it at 2000 rpm - I'll do that.

There was no electrical stuff on at all.

Thanks,

Ant
A Kittle

I've got a new question... Took the B out yesterday whilst it was still rather damp and she back-fired rather a lot. Felt as though I could feel it coming and avoid them by backing off the throttle... (and on the flip side, cause it to pop and bang by dipping the throttle more). Do you think this could be somethihng to do with damp in the dizzy or something similar? It happened before in the autumn when I took her out on a particular 'misty' day... lots of coughing and popping and even a couple of random stalls... at the time I put it down to a bad day!

Cheers,

Ant
A Kittle

Pull the distributor cap and check it for carbon tracking. This shows up as small lines running from the high tension lead connectors. Check inside the cap as well as the outside. This condition will cause the spark to fail under load. While you're at it check the rotor arm for signs of deterioation also. All of the above will be exasterbated under damp conditions. Ray
RAY

Like Ray, I've had very similar problems on a Metro caused by the cap and/or rotor - I changed both. I diagnosed this by clipping a timing light onto the coil lead and opening the throttle sharply, which was enough to cause the problem in my case. Sparks were regular and consistent, but when I started clipping the light onto each plug lead and doing it it was obvious the sparks were failing. This indicates the cap or rotor are breaking down.
Paul Hunt 2

Cheers Ray and Paul.

I'll have a look at the cap at the weekend.

A
A Kittle

I've checked the rotor and the cap and both look as good as new (well... almost) but no sign of carbon tracking and the HT leads are practically new as is the coil.

One thing I did notice though is that the ends of the spark plugs are rather blackened - is that to be expected? Also - they were bosch plugs rather than Champion... can that make a difference?

Here's a photo of the spark plug:

[IMG]http://i42.photobucket.com/albums/e338/ant-k/spark1.jpg[/IMG]

I realise I'm asking a lot of basic questions - thanks for your patience and advice!

Ant
A Kittle

Photo URL should be: http://i42.photobucket.com/albums/e338/ant-k/spark1.jpg
A Kittle

Rotor and cap problems aren't always visible, they weren't (to my eyes) on both the occasions they have been the cause of my problems. In both cases the timing light test clearly diagnosed the problem.

Bosch, Champion, NGK all make plugs for the MGB but it is the grade that is important. For Champion plugs based on N9Y are the correct grade, for NGK it is BP6, and for Bosch W7. All manufacturers have variations on these for copper core, integral resistor etc. which add varous prefix and suffix letters.

That plug looks sooty to me, which can be caused by a rich mixture. However that wouldn't cause the popping and banging you mentions. It also looks like a 4-electrode, which is what I've had in my roadster for years.
Paul Hunt 2

Thanks Paul - I've decided to bite the bullet and get a Lumenition Magnetronic ignition kit, new dissy cap, rotor arm and give her a full service.

Then I think I'll take her somewhere to be properly tuned.
A Kittle

This thread was discussed between 17/02/2008 and 03/03/2008

MG MGB Technical index

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