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MG Midget and Sprite Technical - Missed my MOT

A bit dissapointed as the car didn't even make it to the MOT station. I took it for a test drive in the morning, about a 1.5 miles, and it ran well with no issues, went for another test drive after 10 minutes having fixed some rattles, but after half a mile it started to emit a funny rattling, banging sort of noise. It managed to get home but sounded worse, so I left it.
Half an hour before it was due for its MOT I tried to start it, it turned over well but really shook from side to side and refused to start.
As I suspected that it was an electrical fault I tested one of the spark plugs, it didn't spark.
I have replaced the HT leads and rotor arm, the points, ballast, cap and 12v ballast all look very new, however I feel that the problem lies within the coil, is there a way to test it? and am I missing anything obvious.
Thanks
BH Harvey

Check that the distributor hasn't slipped and changed your timing. Would cause all the symptoms you mentioned.
B Young

Turn over the engine and see if the coil sparks direct....

If it does not the the rest is fine
Onno Könemann

I have never checked the timing so it could have gone from bad to worse, however surely even if the timings out the plugs will spark, wont they?
BH Harvey

Just checked the coil for spark, nothing when the engine is turning over.
With the key in position II I have 12v across both inputs yet only 9v on the output, this goes down to 8v when the engine is turning over. Does this sound right?
BH Harvey

Sounds a bit suspect to me. Which model are we talking about as the 1500 ballast is part of the loom?

12v in position II with a ballast resistor suggests the points are open. This being the case, you should get 12v on both the input and the output. With the points closed you should have about 6v at the inputs and 0v on the output.

Even then this doesn't confirm the coil is good!
The coil is actually made up of two coils. The primary winding between the two terminals and the secondary between the -ve terminal and the HT output.

Use a meter on resistance between the terminals and you should get low number approx 3-6 ohms, then check from the -ve terminal to the HT output. I can't remember the exact resistance but that's not an issue as long as you get a reading.

After all that messing around it still doesn't confirm the coil is okay! It is possible the internal insulation separating the two coils is breaking down when the high voltage needed for ignition is generated.......

I would go for the easy fix and change the coil just to eliminate it... you can always keep the old one as a spare/trouble shooting tool if its not faulty!!!

MGmike
M McAndrew

I decided to replace the coil with a new ballasted coil today as I could hear liquid sloshing around in the old one, and a spare is always useful. However even with this it failed to start (except once for about 20-30 seconds), it sounded like it was close though as the coil was sparking but not the plugs. Now I am beginning to suspect the capacitor.
BH Harvey

And don't worry about the liquid; it's cooling oil.
Alex G Matla

I know its about MGBs, but read carefully the article Paul Hunt wrote on coils. It explains much. For example, your reading of 8 or 9 volts points to it being a 12 volt coil on a ballasted circuit. Look at this: http://www.mgb-stuff.org.uk/ignitiontext.htm#coil
Mike Howlett

By that article the original coil was probably working fine, it said it was a 12v coil but is probably a 6v with internal ballast to produce a 12v coil.
Capacitor failure seems fairly common, especially with new capacitors, http://www.britishcarforum.com/tikiwiki/tiki-index.php?page=Condenser+Failure+in+Conventional+Ignition+Systems. Is there a way to test it, without buying another or removing it (the orange wire is soldered to a black wire leading out of the distributor body)?
BH Harvey

BH there was a recent thread which IIRC included stuff about testing the condenser

also have this link - http://www.distributordoctor.com/distributor_condensers.htm

Dont take this the wrong way but you need to follow a logical step by step diagnostic at the moment you seem to be jumping from one idea to another which may find the problem but might not give you the reason for it

A copy of this Porter Manual may help you as it includes diagnostic flow charts as well as full servicing details with just a few typos in specifications MG midget and Austin-Healey Sprite Service Guide (Porter Manuals)
http://www.amazon.co.uk/Midget-Austin-Healey-Sprite-Service-Guide/dp/1899238077

I think sometimes you can over analyse things with a multi-meter and a simple test light can be better

Hopefully Bob and/or Guy will be along to walk you through the stuff

two things Id say, dont assume that new parts cant be faulty and the fact that it started once for 20-30 seconds possibly suggests timing check dissy retaining ring is tight
Nigel At

The distributor is tight, although the base plate is a bit loose. Should I try resetting the timing?
BH Harvey

....Should I try resetting the timing?...

No

Do you have a multimeter? Or do you have an automotive test light?

If you aren't getting sparks there may be a problem with the rotor arm or the plugleads, but.

We need to know what car you have, it sounds as if you have a ballasted system, if so you should have higher voltage at the coil when it is cranking. You get a bypass to the ballast resistor when cranking to improve the spark voltage on startup.

Are you certain there are no short circuits on the wire from the coil to the points? This would stop it sparking.

Start at the beginning, we can guide you from there
When the engine turns over are the points closing and opening

Take the cap off the dizzy and the LT wire from the coil before you look, that way there will be no stray sparks

If the points open and close (this bit is the most important closing makes the cicuit from the ignition switch run through the coil) put the LT lead back and watch as the points open when you crank it,can a faint feeble spark can be seen at the points?

Check this and come back
Bill 1

Just a variation on that last note of Bill's: When you replace the LT lead and before you put the dizzy cap on, it is easier to just flick the contact points open and shut with a thumbnail or a small screwdriver. You should see a good spark across the points. I find this easier than cranking the engine and watching for the spark.
Guy

Sorry I forgot to mention that my car is a 1978 1500. I cannot get a spark at the points with or without the engine cranking, witch is odd as i'm sure there were sparks in that area yesterday. Here is a overview of the ignition.


BH Harvey

And the distributor. I'm not sure whether the capacitor wire should be clamped like this, it doesn't look like a good connection.


BH Harvey

Well that looks fairly typically badly assembled where the wire is crimped, check that the crimped section is making contact with the bent metal joining clip, it may have gone "open circuit".

From the pictures I cannot see the vital point where the LT wire is clipped to the spring, a slight misalignment here can short the ignition line to earth. Which would stop any sparking being produced.

If you still have 12v at the coil you should also have it at this connection.

Is the wire connection pigtail plugged in correctly?

If so and the points properly aligned (yours looks a bit offline) you should pass the GuyTest and get a spark when you flick the points .
Bill 1

BH you've got the help you need now

Bill don't forget at the relevant points to throw in dissy lube/oil and to allow for and tell of battery depletion/recharge (cells, water) :)
Nigel At

I installed another condensor and in doing so found that the LT wire was practically worn through. I'm not sure whether my insallation is correct, the LT wire is touching the base plate.


BH Harvey

I don't know whether the earthing wire shown is necessary, if it is then it indicates that the base plate is earthed and thus that the spring connector should not be touching it.
Is there a way to adjust points without gauges?
Thanks


BH Harvey

I had a LT cable which was broken from new straight out of the box. It turned out that cable under the braiding was broken.
Gary & Gaps

OK

The nylon doohikkey that the points spring sits in is supposed to stop the LT wire shorting out

There is supposed to be a braided earth wire which means yours is right, oh arr, yes your old LT wire looked very badly frayed from the pictures you showed

So basically you need to ensure that the LT wire isnt touching the body of the dizzy, then you should get "switching" when the points open and shut

To get the correct gap is a matter of practice, after doing roadside breakdown repairs for many years I could get pretty well "on size" by eye, which I usually confirmed with my dwell meter but you really need sonething that is 0.015" thick to slip between the faces of the points

A plastic credit card is about 0.025" so in a pinch that could be used to get you going but isn't really good enough for all day use

Ideally you need a set of "Imperial Feeler Gauges", very cheap usually and better than mucking about guessing

As Nigel will no doubt remind me, when you have the points opening and shutting add a drop of lubricant to the cam that controls the opening points, this will prevent the cam lobes wearing away the tip of the plastic on the points

Lubricant? I usually pull the handily located dipstick out of the sump and let one drop fall between the cam and points, then drop the stick back in t'hole.
Bill 1

The LT wire and the yellow condenser wire need to be fastened in such a way that they connect to the curved points spring, with the neoprene / plastic insulator preventing contact with the metal of the base plate.

Guy
sorry, double messaging whilst Bill was giving his more complete answer!
Guy

as usual the owners Handbook is your friend here

that screwhead and previous wire tell a tale

Bill are you not one for lubing the cam (heel is it)

personally I'd suggest you show that rotor arm the bottom of your recycling bin and swap it for a good one such as - http://www.distributordoctor.com/red-rotor-arms.html

explanation - http://www.distributordoctor.com/rotor_arms.html

if you replace the rotor arm and clean the inside and out of the dissy cap and check it for condition including the sprung carbon brush - if in doubt renew the dissy cap, they're cheap enough and better that it's not a cause of future rough running or a breakdown

you'll also need to check the points gap after a few weeks or good few miles after you set them this time, PITA they are

>>The distributor is tight, although the base plate is a bit loose<< has this been discounted?

Nigel At

I put a bit of electrical insulating tape between the spring and base plate and now it sparks at the points, it still won't start though.
The movement in the base plate feels right (ie not like something has broken/come loose) and so I ignored it. I'm pleased to say that it was not me who mutilated that screw head.
BH Harvey

Of course, that little two-pronged fork thing on the baseplate next to the cam should have a little felt wiper thing in it to drip your oil drops into. Surprised Nigel hasn't mentioned it. It must be in the Handbook
Guy

Guy has it right (of course) with the missing felt pad, was there not one in the box with the points?

Nigel, I found that if once lubed as I described the heel on the points plastic lived for a long time. (initial wear seems to take out the heel in a very few days and when worn past an initial softness they then lived 'til the points eroded away.) The "modern" version of the Lucas contact set that is in this dizzy should have the additional oily pad to keep the lobes greased, not visible here on these pictures.

You asked for a way to test the coil

one test

put the dizzy cap back on the dizzy, remove the spark plugs and pop each one into a plug lead, prop the plugs against the head so that each plug is earthed at the body

Crank the engine and look at the electrodes on the plugs

Sparks?

Good it works
No spark?

Take the king lead (coil to distributor) out of the dizzy and stick one plug into it and crank the engine again with the plug body earthed as before

Sparks (lots of 'em)

faulty cap or rotor arm 'cos the sparks are getting shorted somewhere before reaching the sparkplugs in the head, probably in a crack or a deep pitted burn under the rotor arm centre

No sparks at all

you need proper advice and a handy mechanic to spend a half hour with your car, which is where a local club can be of help

If you were just round the corner I'd pop round

But.................
Bill 1

Guy
I can’t remember that bit of felt, I’ve not had points for many years

the felt that covers the screw in the centre of the cam is there, I used to lift that bit of felt to put a drop of oil passed the screw as well as through the plate

an older friend of mine that likes tinkering with cars swears by points, I swear at them, not had them since a replaced set decided to shut themselves down a few weeks after replacement

admittedly gapping the points is easier on a 1500 but on a 1275 it’s a pain in the back at least

Bill,
you’d know a lot better than me about the lubing, I thought there seemed some big gaps but couldn’t remember - I go for as many maintenance-free components as much as possible on these cars, apparently there’s nothing for me to do on the 1-2-3 Dissy other than check the rotor and cap and that I like

BH
I wasn’t blaming you for the screwhead and it’s good that you checked the baseplate

I misunderstood I was thinking of the dissy clamping plate, the locking plate around the base of the dissy stem that locks it in position to the engine block – was/is loose(?) - I know you said the dissy was tight so this may have already been covered and you did mean the baseplate

Not trying to tread on Bill’s toes and the dissy turned would have been too convenient
Nigel At

After trickle charging the battery (it was completly flat) and adding some new fuel to the float chambers it started up first time. Booked the car in for its MOT tomorrow.
Thanks to everyone who posted advice.
Ben
BH Harvey

Ben if you're interested I've done a Zip file of advice notes, nothing tecnical just experience from 20 years of using classics as dailies

just email me

nigel

atkins

at

bt

internet

dot

com

all lower cased
Nigel At

Nigel, likewise I am electronic. At least my car is. Ex MG Metro dizzy. But I do recall on earlier cars some , though not all, had a small greasy felt "wiper" fitted in that forked protuberance from the base plate.

I think also that its OK for the base plate to feel a little loose. Doesn't it "float", and move with its attachment to the vacuum advance wotsit?
Guy

Guy I'm lucky if I can remember this afternoon let alone years ago, I'm sure there should be a piece of greasy felt I just don't remember it

I didn't meant the baseplate(?) inside the dissy I meant the clamp plate around that holds it for timimg
Nigel At

Ah, yes, the clamping plate should be secure. They often get overtightened and then distort. People seem afeared of the timing "slipping" In my experience this is extremely rare. Timing doesn't just slip of its own accord on A series engines. Once set,it is set until you choose to alter it. Unlike the magneto on my old M21 which would constantly adjust itself!
Guy

Ben that is good news, well done

Nigel

My toes are tread-upon-proof mate :-)


I only stepped in with Ben 'cos he needed a little direction to get it working

My days of diving in to every problem, guns blazing are far and away long gone

Oh yes as Guy mentioned, the later type "Quickfit points" have a little felt pad which slots in the bracket on opposite side to the points heel, this is greased inside its box ready to fit, Ben probbaly missed it when he opened the package, it's in a very small folded bit of greaseproof paper

I'm happy to help if I can, like so many here, if we can keep old car's owners happy we can keep the cars alive too
Bill 1

There are a few Spridget owners meeting at the Angel, Addington, Kent. at 1200hrs this coming Sunday. Should be at least one other 1500 Midget there if you have time to apare.
A Anstead

This thread was discussed between 19/08/2011 and 24/08/2011

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