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MG Midget and Sprite Technical - No Spark

I have a 1975 1500 midget and I no spark. I have changed the points, condensor, rotor arm and distributor cap but still no spark. I am presuming that it must be the coil as there is power at the +terminal. Is there any way of checking the coil? Also if it need replacing would it be ballast or non ballast coil.
matthew grindrod

Matthew,
When you changed the points are you sure that you got the insulating spacers in the correct position to isolate the spring strip from the base plate post? Its a very easy mistake to make - and very effective at producing zero spark!
Guy

Yes they have been installed correctly.
matthew grindrod

"I have changed the points, condensor, rotor arm and distributor cap but still no spark. I am presuming that it must be the coil "

I would check your main HT lead before anything else, if you are certain that you have eliminated all the other items.
Lawrence Slater

Whats the best way to check the lead?
matthew grindrod

Read the thread below entitled TDC help + dizzy question
Dave O'Neill2

Checking a coil is VERY easy

However why did you change all that lot?

When was the last time the engine ran?

Switching on the ignition should put voltage to the positive on the coil.

If you are competent with a volt meter then you can do the following to check the points

With the points Open measure voltage between negative on the coil and earth (engine) thi on a 1500 should be about 8 volts. Now with the points closed this reaing should drop to about zeo.

I that is the case then disconnect the main lead from the centre point of the dissy cap that is fom the coil. place the end of this next to the engine block and turn the engine so the points are closed. Now with the ignition on flick the points open and close. Each time the points open the lead from the coil should spark to the engine block if the gap is small enough

Alternaively to check the oil you can simply remove the wire from the negative terminal of the coil and with another tempoary wire onnected to the negative of the coil simply flash this wire to earth and again watch for a spark to jump from the main coil lead to earth

Hope this is clear.

What page are these tests on in the drivers handbook Nige?
Robert (Bob) Midget Turbo

Driver's Handbook for prevetion others books for repair - you obviously missed my previous response to your last question on it

the Driver's Handbook does tell you how to fit the parts correctly as part of the servicing

and includes lubbing the dissy and CB points which most don't bother doing

not everybody has your knowlege Bob some of us have to aquire it from books :)

not that we can remember it, but we can always got and have look at the books again to refresh our memories
Nigel Atkins

Bob's advice, if you have a meter is good. If not then a really quick and easy way to check the LT (switch, ignition wiring and contact points) is this:
Remove dizzy cap, turn engine so that points are closed, switch on ignition and then with your thumbnail or a small screwdriver, just flick the points so they open/close. They should show a bright spark. If not, then your fault is "upstream" of the points. If it does spark, then either all is well, or the fault is "downstream" of the points, and possibly with the HT cabling.

Guy
PS, whilst the cap is off, check that the little carbon brush in the centre hasn't gone walkabouts.
Guy

Guy I thought that was the test I had described?

from above
""I that is the case then disconnect the main lead from the centre point of the dissy cap that is fom the coil. place the end of this next to the engine block and turn the engine so the points are closed. Now with the ignition on flick the points open and close. Each time the points open the lead from the coil should spark to the engine block if the gap is small enough""


Or from the previous thread
""Always try with a dissy that has points. With the dissy in a position where the points are closed and ignition on flick the points open? Do you see a spark across the points?"

ery easy as you say

Robert (Bob) Midget Turbo

Sorry Bob, somehow saw your reference to a meter and the desirable voltage and missed the following practical "easy steps" advice! "Works hard, but must take more care" - it's what I used to get on my school reports 50 years ago.
Guy

Well I used to get "pay attention and must try harder"

I think they made a rubber stamp with those comments on because I always seemed to get the same report!!

LOL.

We tend to read what we want to read sometimes/most times and miss the obvious.

And most times the problems with these boards are that the easy things to check whilst being totally unecessary are the ones that posters choose to try.

It is very easy to simply change everything instead of the simple test we have described because that requires effort to read and understand how to do it and that is a problem.

My pet aversion is those that suggest guessing what a problem is or changing parts willy nilly

Rant over!

Sometimes history can help but in 45 years of working on Spridgets I have never come across any of the issues faced by Prop!! LOL
Robert (Bob) Midget Turbo

Thanks for the advice I will attempt it tomorrow!! The car was started about a week ago, I replaced the parts because they were relatively cheap and havent been done for some time.
matthew grindrod

So is it fair to say then Matt that it was OK until you did the service?

If that is the case then the tests ought to display that the points are installe incorrectly, but I am guessing and testing will solve the problems.

For reference regardless of what the handbooks states parts last almost forever.

I have NGK spak plugs that I fitted many many years ago, same withmy dissy cap that was put on in 1990 and only removed along with the dissy when replaced with programable ignition. I can't remember he last time I found it necessary to replace a condenser and my MGA has had the same ignition parts in for about 10 years.

I am tight and only change parts when they are kn4ckered!
Robert (Bob) Midget Turbo

Matthew,
"I replaced the parts because they were relatively cheap and havent been done for some time."


----Bad move I'm afraid.

X2 what Bob said.
Don't follow the advice in the service intervals in the User manual or workshop manual too literally. I have had the same rotor arm in for years, same plugs, same condensor bla bla. And as far as I can remember, the same coil since I bought the car in 1977. ('66 Sprite). I can reach 100mph, so it must be working ok, and I bet yours is too.

It does indeed sound like you've induced a fault where there was none before, so it'll be easy for you to fix it.

Then, I hope you haven't thrown your old points etc away, as they will be useful spares.


Lawrence Slater

Guy,

Please confirm if my understanding is correct:

downstream comprises spark plug, plug leads, dizzy cap and rotor arm

upstream comprises points, LT lead, coil, main HT lead and ignition switch

Thanks,
Doug
Doug Plumb

Upstream (Low Tension or Low Voltage) comprises, battery, ignition switch, low tension lead to coil primary winding, low tension lead to points and condensor - from coil primary winding. In that order.

Downstream (High Tension or High Voltage), comprises, coil secondary winding, main HT lead, distributor cap, rotor arm, plug leads, spark plugs. In that order.
Lawrence Slater

The parts were replaced after the problem in a attempt to correct it. The car hadn't been run for several weeks and on starting it fired once but then just turned.
matthew grindrod

disconnect the main lead from the centre point of the dissy cap that is fom the coil. place the end of this next to the engine block and turn the engine so the points are closed. Now with the ignition on flick the points open and close. Each time the points open the lead from the coil should spark to the engine block if the gap is small enough - I DONT HAVE A SPARK WHEN I DO THIS

Alternaively to check the oil you can simply remove the wire from the negative terminal of the coil and with another tempoary wire onnected to the negative of the coil simply flash this wire to earth and again watch for a spark to jump from the main coil lead to earth - I HAVE A SPARK WHEN I DO THIS

Any ideas?? new coil needed????
matthew grindrod

Good stuff Matt

If you have done the tests as described and it sounds like you have then the coil is fine!!

What is at fault however is that the points are probably installed incorrectly.

Now when you did the initial test and flicked the points open and closed not only should the coil have sparked to the engine block but you should also have noted a spark flashing across the points as they were flicked open.

The problem when new points are installed is the insulator on the achor post. The sprung metal arm of the points that attaches to this post should have a plastic dowel inserted between it and the metal post. this prevents the poits from touching the metal plate of the distributor and should also protect them from the anchor nut on the post.

Also 2 connections should be made to this points sprung arm, condenser and the lead from the side of the dissy. If these od not make contact with the points sprung arm the car will not work.

So you need to ensure that the poits sprung arm is making electrical contact to the condenser and the lead from the side of the dissy but all three connections should be insulated from earth (metal post) by the plastic dowel/washer
Bob Turbo Midget England

a clear drawing and details of this and other servicing details and full schedule are in the Driver's Handbook - (Ref: 0058) http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html - including the oft forgotten lubbing of the dissy
Nigel Atkins

This thread was discussed between 08/02/2012 and 17/02/2012

MG Midget and Sprite Technical index

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