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MG MGB GT V8 Factory Originals Technical - Ignition/coil

I have had a Sparkright/Sparkwell (?) electronic ignition on my factory V8 for the past four years - it came with the car - and over the weekend I had problems starting it. I called out the AA who, luckily had knownlegde of points and distrubutors, checked it all through and pronounced the sparkright/well unit dead, hence the car wouldn't start (it was probably 20-25 years old!). So I've stripped out the sparkright/well and replaced the coil with a non ballasted coil, and it works, but not very well on damp mornings, it used to start regardless of the weather. What are my best options? Should I replace the sparkright/well with another or modern equivalent, or keep the non-ballasted coil in place, or put a ballasted coil in with the neccessary wiring to make it work? What did a 1975 factory V8 have when it was new? Any thoughts would be appreciated, Thank you
Mark Bushby
Mark Bushby

Others can tell you better than I (ie Paul) however the ballast set up is simply a 6 volt coil with a resistor that takes the voltage (ie 12v) fed to it down to 6V. The point is that the starter motor has an addittional terminal that is connected to a wire that runs directly to the coil and bypasses the resistor. This terminal is only live when the starter is cranking. This means that when the starter is cranking it feeds 12 Volts to the coil instead of 6. The coil produces a big fat spark (which helps starting) and overheats just a little, which doesn't matter since the cranking doesn't go on for too long.
You should already have the wiring in place, a wire from the starter. ie buy a 6V coil and ballast resistor and wire it so that when the car is running the voltage fed to the coild goes through the resistor. Obviously attach the bypass wire from the starter direct.
Be aware that the ballast resistor gets warm/hot.
Peter

Mark

The V8 ballast is in the wiring - you want a GCL111 coil or Bosch 0-221-122-392 which was fitted to the RV8 with an amplifyer.

If you replace your sparkrite - the luminition works but is expensive - the RV8 system is available secondhand - and be sure to carry a spare.

Roger
RMW

As above the V8 had a 6v coil with ballast resistance within the loom. I would have thought that a Sparkrite system (I still have but not installed a self-build kit that used the original points from the 70s) would need a full 12v supply so your loom ballast may well have been bypassed. The coil may also have been changed for a 12v one, but this may not make that much difference with a capacitive discharge system (which mine is) which whacks a few-hundred volt pulse into the coil to generate the spark rather than the standard system passing a current through the coil for a relatively long period. With the conventional points/coil ignition using a 6v coil with an unballasted supply will cause excessive arcing and erosion of the points and overheating of the coil. Conversely using a 12v coil on a ballasted system will result in a weak spark.

You must determine whether you have a ballasted supply to the coil or not, and whether you have a 6v or 12v coil. The latter is easy, the primary of a 6v coil measures about 1.5 ohms and a 12v about 3 ohms. A Lucas Sport coil I have measures about 2.4 ohms.

With a ballasted supply, with the ignition on and the points closed, you will measure about 6v on the coil +ve. With an unballasted supply you will measure about 12v.
Paul Hunt

Thanks all. I have - I think - both feeds available to the coil! At the moment There is a new direct feed to the coil from new wiring direct from the fuse box. Also there is an unused spade terminal on original wiring which is not being used, but has a wire coming out of the loom with it that supplies the rev counter, I presume that is the ballasted wire.
I'm using a 12v (?) coil (3letters then 101 written on its side) and the direct feed, but I'm wandering whether the ballasted set up would be the better bet for damp and wintery conditions?
Mark Bushby
Mark Bushby

A ballasted coil can make the difference between starting and not starting under adverse conditions, as long as the boost contact on the solenoid is connected and working. This will be white/light-green on the +ve side of the coil the same as the feed from the ballast and may be the wire you are thinking of. The tachometer (strictly speaking a rev counter is the mechanical device off the crankshaft) feed is a white/black from the -ve side of the coil with a second wire to the points.

GCL101 is supposed to be a 12v coil, but with screw-in HT. The later 12v coil with push-in HT was GCL110, and the 6v coil GCL111. Possibly. I'd still measure it.
Paul Hunt

This thread was discussed between 07/09/2004 and 14/09/2004

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