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MG MGB GT V8 Factory Originals Technical - Coil recommendations

Hi all,

I have been having ignition problems on my 3.5 Range Rover engined MGB so I have removed the electronic distributor and replaced with a points one.
Can anyone recommend a 12v coil to use on this system as I have read that i cannot use the original coil as it is only for electronic ignition?

thanks
Steve D

It depends on the ignition wiring as well as the system as to what coil you can use.

Chrome bumper MGBs used a 12v coil, rubber bumper MGBs used a 6v coil as they had ballasted ignition wiring.

Many V8s used basically the same ignition system as the 4-cylinder MGB and so are interchangeable, and if you have been able to substitute a points distributor for an electronic distributor then in most case you would be able to use the same coil.

But it all depends on what ignition wiring and coil you had to start with, if you get the wrong combination you can either get weak sparking or an overheating coil, so you will have to do some voltage and resistance tests before you can decide what coil you need. Fortunately it is easier to do this with a points distributor than it can be with an electronic.

Turn on the ignition, make sure the points are closed, and measure the voltage on the two low-tension terminals of the coil i.e. the spades.

If you measure 12v on one and 0v on the other, then you have unballasted ignition wiring and so need a 12 coil. If you see about 6v on one terminal and 0v on the other you have ballasted wiring and need a 6v coil.

Standard 12v coils measure about 3 ohms between the two spade terminals, or about 2.4 ohms for a 'sport' coil. 6v coils measure about 1.5 ohms, or about 1.2 ohms for a sport. Don't go by what the coil says on it, or what it says on the box, or what the salesman tells you, always measure the coil, that is the only way you know what you are getting as so much information about coils is confusing if not down-right incorrect. Note that coils for some special electronic ignition systems can measure as low as 0.1 ohms, if you try to use one of these on a points system you will burn your harness.

At the end of the day the coils for a points distributor V8 are exactly the same as for a points distributor 4-cylinder engine, the important thing as I say is whether you have ballasted wiring or not, and to make sure you have the correct resistance for that. You can't even go by whether your car was originally a chrome bumper or a rubber bumper, as someone may have added a ballast to a chrome bumper or bypassed it on a rubber (or *added* ballast to a rubber and then used a 12v coil as I have seen in the past) which is why you must always measure the voltage and resistance.
Paul Hunt

Paul,
thanks for that information just what I was after
cheers
Steve D

This thread was discussed between 30/07/2009 and 01/08/2009

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