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MG MGB Technical - Electrical problem

Used the car today, everything working then went to use it again but no current (electricity) - everything dead apart from a couple of clicks from somewhere in the engine compartment when turning the ignition key.
Any suggestions for what it could be?

Moss. First, battery connections. They should be clean and tight on clean battery terminals. Second, the connection from the battery to the starter solenoid. It, too, should be clean and tight. If any of them are not, it can cause starting problems and, in some cases, can result in the battery not being properly charged.

After the engine is started, check the charging voltage of the alternator. Should be 13.5-14.5 volts at 1,000 rpm and above.

Les Bengtson

Les, thanks for your advice. Have now solved the problem - I checked the ignition coil connections and found that the wire (in two parts) from the minus terminal on the ign. to the dist., where they are joined together, was covered in oil - it was positioned so that it ran underneath the oil cannister. So I presumme that there occured a short because of the oil on the connection between the two halves of this wire to the dist.
As with these things I have also discovered that my ignition coil is not a ballast type (I have a USA 77 model) when it should be. There is no wire from the plus terminal to a ballast resistor.
Oddly enough the engine now starts very quickly and seems more though it has got more spark.

Moss. Your solution is inconsistent with your problem--your need to keep looking.

Your original complaint was: - everything dead apart from a couple of clicks from somewhere in the engine compartment when turning the ignition key.

The input line to the coil would not cause such a problem, even if both lines were making poor connection due to a bad terminal/bad connector/etc. The gauges would still begin to indicate when the ignition switch was turned, the starter would turn over (but the engine might not start without power to the coil), turn signals and hazards should flash, lights should come on, and the horn should sound--all of these should work fine if the only problem you had was bad connection to the coil.

Much different than what you have described. Hence, I suspect that you will have the problem again unless you can trouble shoot and find the root cause of the problem.

Now, let us look at your old car which, as you note, is a 1977 MGB to the North American Specification. An interesting model year which I have some degree of experience with as we purchased one for my older daughter, when she was 15 1/2, to help restore and learn to drive on. She is now 28, just had my second grand child (boy) and still has the MGB.

The 77 was interesting because the wiring diagram was a "77 Supplement to the 1976 wiring diagram" rather than a stand alone document. My daughter's 77 shows some portions of the wiring that are similar to the 76 model year and others which are different and more closely approach the "78-80 model year" wiring diagrams. Always makes it interesting to do electrical troubleshooting, especially considering the amount of "home modified/reconstructed" rewiring that has been done over the years.

So, with all of that in mind, let us examine "As with these things I have also discovered that my ignition coil is not a ballast type (I have a USA 77 model) when it should be. There is no wire from the plus terminal to a ballast resistor".

First, there is no "ballast resistor" in the MGB ignition system. The MGB used a resistance wire--i.e. a wire that has some form of internal resistance but looks like a normal piece of wire from the outside, to drop the voltage to the coil when the ignition switch was in the run position. When the ignition switch was in the start position, the starter solenoid was activated, through the starter relay, and while the starter solenoid was being powered it sent a supply of 12v current to the positive side of the coil through a spade terminal on the solenoid which is located just above the terminal for the wire coming from the starter relay.

So, the system, when the ignition switch is in the start position, supplies 12V input to the positive side of the ignition coil. When the ignition switch is moved to the run position, power to the starter relay is terminated which causes loss of power to the starter solenoid, which terminates the 12v input to the coil. But, the white wire circuit is still providing power, at a reduced voltage, to the coil so the engine continues to fire the cylinders properly. This is the factory set up and was used with both the Lucas 45DE4 (Opus) system used on the 77-79 MGBs and with the Lucas 45DM4 (CEI) system used as a replacement for the earlier system and as standard on the 80 models.

What you have, today, in your car has to be examined and checked out. The Opus system was junk and I have never seen an intact one. I have heard claims of intact systems but, when I have been able to inspect the claim, the internals of the dizzy had been replaced with some other form of triggering device. I doubt, very much, that your car has an original, intact, functioning Lucas 45DE4 distributor. None of my cars have.

One common conversion, especially when you have an older distributor which needs both a rebuild and a conversion, was to purchase the Lucas 45D4 points type distributor, called the "Euro-Spec" and install it. The kit, as supplied, came with a Lucas Sports Coil and instructions on how to modify the wiring to provide full time, 12 volt, input to the new coil with the ignition switch in both the run and start positions. That may well be what you have with your car and would fit the description you have given us.

Read this a couple of times and if there is anything you do not understand, ask about it. Again, your solution does not fit your problem indicating the problem is still there and waiting to recur. Hopefully, I have provided sufficient information for you to trouble shoot sufficiently well that you can identify the root cause of the problem when it recurs.

Les Bengtson

Thanks for the advice/description. Yes, I'll have to read your text a few times to understand the content.
I can inform you that the car has a reconditioned engine from Ivor Searle UK done in 2008 - to engine specification 846/847, a weber 32/36 carb with eletronic choke.
Just to let you know that all I did was disconnect the battery, remove the ign. coil, cleaned it, sorted out the wire named before. It then started as descibed...
I'll get back to you...

I think you just answered the question Moss. Removing and refitting the battery connections has cleaned them to the point where they can pass the current for the starter motor.
You should now put some petroleum jelly over them to keep corrosion out. I have also had good results with lithium grease. I think the key thing is to keep water out of the connections. However as I understand it you can fit and tighten the clamps after applying petroleum jelly.
Stan Best

That's it, smear petroleum jelly over the post and connector before fitting. It prevents the white fluffy corrosion that can occur on battery connections, but doesn't inhibit current flow once the clamps are tight. If you only smear it on afterwards corrosion can still occur.

Oil around the coil/distributor wire is irrelevant, oil doesn't conduct electricity, on the contrary it is an insulator.
PaulH Solihull

I agree with Stan that the battery connections was probably the problem.

Although not proved as the solution, it does point out what seems to be the more common answer to most MGB electrical problems, 'the simple solution'. I and many other owners of these cars, when a problem, get into a round of all sorts of reasons and find ourselves in some complex trial fixes that only go to cause more problems, maybe now two or three reasons why the car will not start or run.

One of the best books on MGB electrical problems and simple solutions based on good undersstanding of the car is Rick Astley's "MGB Electrical Systems". I believe all B owners should have a copy.
Barc Cunningham

Thanks for the comments so far. It's a conundrum!
A few points:
1.The battery terminals were and are good - no rust or corrosion or fluffy bits :) Battery is only 18 months old. I only disconnected the battery because I wanted to disconnct the igntion coil.
2. I cleaned the terminals on the ign.coil and rerouted the tension lead to the distributor after cleaning off all the oil.

Les is right so far as the wiring to the ign.coil is a bit odd....more later with a few pics



"The battery terminals were and are good"

If the battery and all its connections to earth and the starter were good the engine would have cranked as normal, unless the starter or solenoid were faulty. Clicking under the bonnet when you turn the key and the starter doesn't turn the engine is the classic symptom of not enough current reaching the starter, which can be bad battery, bad connections, bad solenoid or bad starter. If the battery or its connections to earth or the solenoid were the cause the ignition warning light would go out as you turn the key to crank. If it stays bright it is the solenoid, starter, or possibly engine/gearbox earth strap, however in this last case the engine usually turns over slowly, but the accelerator, heater and choke cables get hot.
PaulH Solihull

Further developments - the starter is now whiring for a second or so after engine starts. And the clutch is making a constant horrible whining sound when clutch pedal depressed to the floor. Pedal up no whining, pedal down constant whining - oh dear, sounds serious. Release bearing?...

What year car is it ? If its a pre engaged starter. T
these have a solenoid that moves the pinion in to the ring gear before the motor is powered, it does the same when the ign is turned off. So this could be problems with the solenoid, or damage to the ring gear.
If so I wonder if your earlier problem was the solenoid failng to engage?
Otherwise its a Bendix inertia starter. I have found a tiny smear of machine oil works wonders on them although they are supposed to be run dry. The oil is said to cause dirt to stick to the mechanism causing it to jam, but if its jammed already...
If its a worn/damaged ring gear then its bas news
I would fix this first and see if the other noise goes away. Yuo can still drive the car with a squeaky clutch and sometimes its just rust and they stop with use.
If you have a ring gear problem you would change the clutch while doing that anyway.
Stan Best

The clutch issue does sound like release bearing, mine did that when fully pressed down for some time, before it finally wore through and broke.

I can second putting a drop of oil on the spiral of inertia starters being better than scrupulously clean and dry. But as a 77 (I assume from your profile) it really ought to be pre-engaged, in which case it sounds like the solenoid sticking operated for a while now, whereas before it sounds like it was sticking released i.e. failing to operate properly.
PaulH Solihull

Thanks for the comments - a question showing my complete lack of knowledge on most things mechanical but what is 'ring gear' - is this the outer ring with teeth on the flywheel, or internal parts of the gearbox?

Yes Moss, thats what I always called the starter teeth around the flywheel. I had a new one fitted when the engine was out for machining the block to go to 1950cc. The old one looked like a disaster with 1/2 the teeth worn away, but it gave no problems in service. I would recomend with your symptoms you change your starter if its a 77 car and use it. The ckutch may settle down once you are driving it again.
Attached is one abiding memory from the European event of the year in voborg in 2000 :-)

Stan Best

There *shouldn't* be an issue with the ring gear with pre-engaged starters, it was the old inertia or 'crash' starters that wear them out, as the teeth on the pinion are just banged into engagement whilst it is turning to some extent. Pre-engaged, as the name implies, inserts the pinion part-way into engagement with the ring-gear before the motor is energised. And a knackered ring-gear wouldn't be causing the motor to whine after the engine has started, that sounds more like the motor is spinning freely while not engaged with the flywheel.
PaulH Solihull

Now I am wiser! Thanks for all the comments - have to now find a engine hoist....I'll bring an update soon. A daunting task awaits me!! My initation ceremony begins...

Hi Noss, I'm not an expert on the pre-engaged starter. The inertia one does come out with the engine in situ, you need to remove the dissi and drop the steering column, (Even though the handbook says you can do it with the column in place. I recomend using the Moss re-alignement toll if you do disturb it.
I do recomend removing the earth strap from the batterie/s before working in this area.
Stan Best

Another symptom with the clutch whine is an increase in engine rpm when clutch pedal up - an increase of 400 rpm - alot. Of course all will be revealed (hopefully) when engine and gearbox out but now gathering all info I get get before going ahead with engine and gearbox removal...

Moss. Assuming your North American specification, 1977 model roadster is still left hand drive, there is no need to even think about the steering column when replacing the starter located on the right hand side of the engine. Nor, when I have done it have I needed to remove the distributor. A somewhat tight fit, but it is possible to remove and replace the pre-engaged starter by doing nothing more than disconnecting the battery ground terminal, then disconnecting the wiring from the starter (label where it came from--i.e. which terminal it was attached to), loosen the top and bottom bolts (watch out--they are of different lengths and need to go back into the correct holes), remove the heavy starter carefully, clean around the hole for the starter in the engine back plate, install the new starter (getting the bolts in place is an interesting exercise), reconnect the wires to the starter, reconnect the battery cable to the negative terminal of the battery, and the job is done. About an hour from start to finish, including placing the car up on jack stands all around (makes it easier for old men when all four wheels are off the ground), then lowering the car back onto the ground. It will take a little longer the first time you do it, but it is not a difficult job--at least on the left hand drive cars.

As to the increased engine rpms with the clutch pedal up (I assume you mean it is not depressed and that the clutch is not being deactivated as when one shifts gears), this tends to indicate that when the clutch pedal is pushed downwards, causing the clutch arm to press the throw out bearing against the pressure plate and the pressure plate to no longer apply spring tension against the clutch plate, one of two things is happening:

First, the throw out bearing is worn out and the cast iron portion of the throw out bearing is being forced against the pressure plate causing a large amount of drag. Or,

Second, the thrust bearings inside the engine are excessively worn and, as the throw out bearing is being pushed against the pressure plate, the force is pushing the crankshaft forwards, causing it to be pushed against the engine block and drag against it. This latter is most commonly found in the midget 1500 with its Triumph engine. I have never seen it present in an MGB or an A series engined Sprite/Midget. But, in theory it could happen even with the better design of the BMC engines.

Les Bengtson

Just looked at this thread last bit, about starters. What is everybodies opinion on These high torque starters? If one were to buy a new starter are these worth it? or case of overkill? Mike
J.M. Doust

Hi Les, thanks for the comments - I do not know for sure of course but I reckon it's the release bearing -the noise is extreme - very very loud screeching. And yes, a 77 USA spec with steering wheel on left-hand side (when sitting in the car).

Geared starter worth it? Debateable.

They take significantly less current than the original type for probably a faster cranking speed. That puts less strain i.e. probably increased life on the battery as well as making for easier starting i.e. less volt-drop for the ignition during cranking, they are also much quieter. That may seem worth it, but at double the cost it becomes debateable in my book, when the original system works perfectly well unless poor condition/setup etc. makes things a bit marginal. I did plump for one on my V8 because they suffer from the heat of the exhaust - even with a heat-shield, but it was crap construction and fell out after a couple of days so I went back to the standard type.

Rev drop when the pedal is pushed down seems quite common according to some owners, even with a perfectly sound clutch, but neither of mine do it and I've never noticed on other cars of the era.

With a 77 of either handing you almost certainly will need to pull the rack (not the column) when getting the engine out, to access the engine mount bolt on that side.
PaulH Solihull

When my original starter motor failed 2 years ago I went for a rebuilt one, despite the geared one being suggested. The party piece cranking is part of the cars charm for me. I can see why for racing you would save the weight.
Our car does drop about 50 to 100 RPM when you depress the clutch. I always thought it was due to the reduced effective mass of the flywheel, mine was lightened back in the 80s, but I suppose it could be drag on the release bearing.
Stan Best

This thread was discussed between 10/09/2011 and 19/09/2011

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