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MG MGB Technical - Going to points distributor, replace coil?

Hello all,
I am going to points distributor on my '77 B while doing an SU conversion. The car has a Crane electronic distributor now.

This may be a dumb question, but do I need to replace the ignition coil? I assume a coil is a coil and it should work with the points distributor.

Thanks! Dave

PS, it's hot here in Atlanta...
David Steverson

The existing coil will be fine.
Ross Kelly

Unless the coil has been replaced with one that's specific to the dizzi it will be fine. You do get things like "Flamethrowers" but once the spark is enough to ignite the mixture, and 18 Kv does that, any more is wasted energy and extra potential to leak to ground. Racers do use 1.5 ohm coils but for road use you will have all the time you need to build the energy in a 3 ohm primary standard coil.
Stan Best

Remember that the late b's had a resistance built into the wire harness (in place of a ballast resistor), if replaced with a different coil this needs to be replaced or bypassed.
John H

As John says the coil must match the ignition feed circuit. Rubber bumper cars had a length of resistance wire in the harness measuring about 1.5 ohms, and the coil primary measured a similar 1.5 ohms, and so ran at 6v. During cranking the harness ballast is bypassed and full battery voltage is applied to the coil (typically 10v during cranking), so boosting ignition voltage when you need it most. Most people seem to bypass the ballast when fitting an after-market ignition system even though it is a retrograde step. They should also change the coil at the same time, but then that depends on what kind of ignition system is being installed as to whether *not* changing it causes a problem or not. Typically pertronix and inductive discharge systems it does, typically capacitive discharge systems it doesn't. Some electronic systems use a very low impedance coil in the tenths of an ohms which *must not* be used on other ignition systems.

If you are going back to points you should really reinstate the wiring ballast if it has been bypassed, and check the coil primary resistance is about 1.5 ohms, replacing the coil if it measures less than 1.2 ohms or more than 1.6 ohms. If you chose not to reinstate the harness ballast then the coil must measure 2.5 to 3 ohms.
Paul Hunt

Yes Paul , it is a 77 car, as you know the clock stopped in my MGB universe a decade earlier.
Stan Best

This thread was discussed on 17/06/2008

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