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MG Midget and Sprite Technical - Different starter solenoids

Whats the difference between the 2 types of solenoid, one having 2 small terminals on one side and 1 on the other, and the other type having the 2 terminals on one side only.

Is the former the 1500 model? If so whats the difference between them?

Is it that the extra terminal on the latter is simply an earth on the unit rather than earthing through the body?

Matt
Tarquin

Matt,
According to the wiring diagram in my trusty Haynes manual, from 1978 on midgets used an externally ballasted coil and the white/light green lead off the solenoid is used to bypass the ballast while cranking the engine. There is also the required white/red lead from the ignition switch to activate the solenoid, the heavy leads from the battery and to the starter motor, and the collection of brown wires to alternator, battery, fusebox and ignition switch.
David "now I have to change my responses on all the ballasted ignition questions" Lieb
David Lieb

Yes the extra connections on the later solenoid are for bypassing the ballast resistor to allow better starting and I understand other benefits as well. :-)
Bob (robert) Midget Turbo

I can never get my head round ballasting. I might have to google it.

So will it do any harm to fit an earlier solenoid to a later car? I've earthed it through the body and it starts fine.
Tarquin

if you are not running a ballasted system it will not do any harm

if you have a ballasted coil you need to run the main coil feed along the ballasted wire to avoid over heating in the coil

(all the extra terminal does is supply 12v at the turning of the key with the key released to "run" that supply stops and if you don't use it for anything it wont hurt)

ballasting isn't as bad as you think to understand

the ballasted coil needs a lower operating voltage to run -
the resistor (a wire in this system, a ceramic block in some others) provides the reduced voltage out of the 12v system -
the "by-pass" wire which operates only when the starter is cranking supplies the full (ish) battery voltage to the coil, which would normally get the reduced voltage -
this makes a hotter spark -
when you stop cranking the coil gets to run on the reduced "designed" voltage it loves -
running the ballasted coil to get you home when the ballast burns out (they do!) is dodgy practise and can b*gger up the rotor arm too -
but it might work for a while -
Bill

Matt,
The only effect of running the earlier solenoid on the later car is that you won't get the benefit of the hotter spark while cranking the engine over with the starter. Tape over the unused WLG wire and ignore it. The ballasted feed to the coil is already in place and will not be affected by the solenoid.

ALL coils are ballasted in order to optimize the spark at higher rpm. Some have the resistor inside the coil and some have it outside. The only reason to have it outside the coil is to be able to bypass the resistor while cranking over to get a hotter spark to start the engine. This is done in 78 and 79 Midgets and rubber-bumper MGBs as well as lots of Chevies, Chryslers, and Fords (and many more, I suppose). Old Chryslers used a lovely ceramic ballast resistor on the firewall. Lots of Chevies used a special high-resistance wire between the starter solenoid and the coil. What do the Midgets use???
David "lots of ballast" Lieb
David Lieb

Can't see how it would hurt the rotor arm Bill, the plug voltage from a ballasted coil fed with 12 volts as opposed to 8 would equal an increase of half as much again. That is in fact less than the present high energy coils that most of us have fitted in recent years without problems with rotor arms as a result.

I had to drive from the South of France one time with a ballasted coil fed with my 12 volt wiring (all I could get hold of at the time in Provence) without problem. Naturally I would expect the coil ran very hot but it did not pack up and got the old Midge plus my wife luggage and me home safely.
Bob (robert) Midget Turbo

Right Bill, I get it now thanks.

So we can run a normal coil in a ballasted system if necessary, but it won't operate at full efficiency, but can't really run a ballasted coil in a normal system permanently.

The 1500 has a pertronix ignition setup, not sure if it's ballasted or not.

Thanks also Bob & David.

So could I jockey the bypass wire off the 12v ignition feed? That gives the same function surely?
Tarquin

I have sent cars all over the country with bypassed ballast resistors, wired to 12v

but it had to be made very clear to people that doing that was not the way the car should be working and should be returned to manufacturer's spec as soon as...

rotor arms do burn out and often it was because of running a "wrong coil" in a system, why? I dunno I dont happen to be a theoretician or a mathematician, numbers? they leave me clueless, not that I'm proud of it, maybe I'm just lazy.

Most often the type of rotor arm that burns out are the Bosch resisted type and I have found these burnt out if a wrong spec coil was fitted

In 28 years of breakdowns, looking at between 8 and 14 cars a day, 7 days on and 3 days off I saw a huge number of burnt out rotor arms. I don't know what b*ggered 'em. I did have to throw them away though

A statistic to warm our hearts though, in all that time I attended hundreds of Minis and probably less than a dozen Spridgets. Loads of Allegros and Maxis too...

My favourite BMC/BLMC jobs (not) however was loss of fuel pumping due to the pump pick up imside the tank falling off in SD1s. We were issued dozens of replacement pick up pipes to fit inside the tanks when this happened. The very last of these I have has become the home to Laras Bike Computer Illumination LED on top of my indicator console. It is a lovely moulded 90º short pipe in 3/8" or 5/16" bore, dead useful.
Bill

Matt,
Better off just ignoring it.

Bill,
Hows about a picture of that LED for the bike computer? In my Midget the tacho readings are 1/2 of the speedo readings (40 hundred rpm equals 80 mph), so I haven't bothered making the Sigma Sport legible in the dark, but I keep meaning to...
David "still in the dark" Lieb
David Lieb

tomorrow OK?
Bill

Not a problem, Bill. The weather will not be conducive to working on Spridgets tomorrow, either ;-(
David "just too lazy" Lieb
David Lieb

Based upon that information then Bill we ought to be seeing huge amounts of rotor arm failures due to the excessive use of high energy coils.

I fortunately have not had such failures but may I ask how many others who have had rotor arm failures were using high energy coils??
Bob (robert) Midget Turbo

please define a 'high energy coil' ?
David Smith(davidDOTsmithATstonesDOTcom

Lucas Yellow sports coil for example see here under DLB105

http://www.speedgenie.co.uk/avonbar/ignition.html
Bob (robert) Midget Turbo

My first EVER rotor arm failure was two years ago when my 1275 midget started to splutter and eventually died. Basically the the insulation broke down at the shortest point to earth this being the top of the rotor.

The car uses the standard non ballasted coil but I was told by a friend at that time that some of his buddies have had some recent failure with various rotor arms with this type of rotor arm and attributed this to some cheap foreign (whatever that means these days) rotor arms.

I did look more closely at the failed rotor arm and could see some voiding in the insulation material where it site over the rotor but I was not sure if this was where the spark energy had eroded and carburized the material.

The new one looked perfect but I carry a spare one anyway now and it is just about the easiest part to replace.

Not wishing to invoke too many extra threads it is possible to use a diode or a relay to bypass a resistor ballast during cranking, if you really need it. Just make sure you put a fuse as close as you can to the point you connect to the starter power.

Dave

Isn't the point of a ballasted coil to provide a 'boosted' HT voltage whilst cranking, rather than a reduced voltage for normal running?

The ballast resistor drops the 12v to around 8v, and the ballasted coil is designed to provide its normal 'full' output on around 8v, whereas 'standard' type coils (sports or any other) use 12v. Applying 12v to an 8v coil gives a bigger spark for starting, which is then reduced back to 8v and normal HT voltage as soon as the cranking is finished.

Richard
Richard Wale

That is what I always believed to be true Rich, however in another thread only last week, when I explained this principle I was told differently by I think Les and David. I am still of the "it is ballasted to aid starting group" :-))

The question here has become a little wider now however with the suggestion by Bill that connecting up a ballasted coil (without the resistor to drop the voltage to 8 volts and so giving it 12) to normal ignition circuit would damage the rotor arm. I have not seen this happen and suggested that it should be no more detrimental than fitting the high voltage/energy coil to our cars as these also induce higher voltages at the rotor arm. What coil do you have fitted Rich?
Bob (robert) Midget Turbo

who cares!

i only wanted to know why the extra terminal - i now know why.

it's not that left field to suggest that continuously putting 50% more energy through a rotor arm might result in problems.
Tarquin

Bob,

Aldon Ignitor, Lucas 'Sports' Coil DLB105, magnecor silicone leads and NGK BP7ES plugs.

The coil and Ignitor have been on 10 years & 26,000 miles, along with a standard rotor arm. The leads were changed from NGK silicone, which began to fail mechanically at the plug connections, about 3 years ago.

I do check the timing occasionally, but it never seems to move!

I do carry a complete points set-up and a coil - maybe I should add a rotor arm?
I will not tempt fate, but so far it's all been very good indeed.

Richard
Richard Wale

Who cares??
I certainly do because if it is the case then using high energy coils may be the reason why so many people have problems with rotor arms lately. If you do not see this or even care tarq then fine but don't flame those who do care thank you!
Bob (robert) Midget Turbo

"can b*gger up the rotor arm too -"


CAN


I did not say it WOULD do that

CAN

however I am resigned to not being read properly for some reason

never mind, at least the thread stayed fairly well in topic for a change

reminds me, I must get a spare Metro rotor arm for my dizzy

David I will pop down to the garage to get you that picture now...
Bill

Posted same time as you Rich. Yes I too have used the high voltage DLB 105 for a good number of years without problems also. Mind I do not change rotor arms simply for the sake of it so perhaps I am using a good quality old one.
Bob (robert) Midget Turbo

Bob, that's just 'snake oil' - there's no spec so probably no different from any other coil ???
David Smith(davidDOTsmithATstonesDOTcom

Bob,
I think you mis-interpreted something there... Both Les and I (at least I, but I believe Les as well) are firmly in the "hotter spark when starting by bypassing the resistor" camp. I think where we were differing is in that the WLG wire from the solenoid is used to BYPASS the resistor, not to insert it into the circuit, thus, when using the older solenoid, the WLG lead only needs to be isolated as this leaves the system always ballasted, in effect, just like the older system other than the ballast being external rather than internal.
David "probably just muddied the water again by not using words like 'swarf'" Lieb
David Lieb

Yes, the resistor is only bypassed (shorted out) during cranking but otherwise is always in circuit during normal running. Think of it as being like turning up the TV volume when the wife starts to vacuum.

D
Dave

Hmmmm

Just when I thought I had some ballast answers (from my old post), it comes back again...rats! All I know is that in my '75 1500, I removed the ballast resistor, inserted a lucas 12 volt coil, and it starts right up. The coil gets no hotter than it ever did, and I haven't burnt any rotors. Also running a fireball ignition sytem that's old, but still works fine. Still confused, but leaving sleeping dogs lie.

Al
ah harad

Al,

12v coil running on 12v = no problem!! Just as it should be.

What is the confusion?

Richard
Richard Wale

This thread was discussed between 22/03/2008 and 25/03/2008

MG Midget and Sprite Technical index

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