Hi all

My brothers mini is getting a tune by a local bloke. He pulled the dissy out and found the springs were not moving so the reciprocal force advance was not working. Anyway.

We were a bit confused as to which coil to use (resister / nonresister) the lad explained the following

Mini's were built with a balast resister in the wiring (usually a bulged wire), which means you need a resister coil to transfer from 12V down to 8v to the coil. However back in the day often people would by-pass this resister and use a 12v coil which often would chew the points out.

My brother needs a new cap and the lad said he wont know which coil to use until he can turn it over to see what voltage is going to the coil (ie whether to use the resister or non-resister coil).

Is this right as i have never heard of minis being built with a Ballast resister?????

Thanks brenton

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I don't believe any round nose had a ballast resistor, not sure about clubmen.

But you have to completely understand what a ballast resistor is all about. The ballast resistor is used with a resistor coil. The resistor coil has a much higher output and therefore a larger input current for a given voltage when compared to a normal coil. Using one in a normal setup will erode your points because of the extra power consumption of the resistor coil.

When starting the car early on a freezing cold morning in Cowra, the solenoid wire from the ignition switch provides twelve volts directly to the resistor coil. This would give an extra large fat spark at the plugs to get the engine started nicely. It compensates for the drop in voltage which occurs when you try to start an engine which doesn't want to turn over very easily (such as in deepest darkest winter). This drop in voltage reduces the chances of a nice fat spark to get you on your way.

Once you release the start button, the coil is fed via a shunt resistor instead. This reduces the voltage to the coil across the resistor (it drops 4 volts across the resistor down to 8V at the coil) and this reduces the current drawn through the points. The spark is back to normal, and the points won't be eroded to nothing.

The point is, shunt or no shunt, make sure your coil matches the setup. A resistor coil is a confusing title. It doesn't mean it's got a resistor in it, it means it is designed to work with one. They have a higher output at twelve volts than a normal coil so cold starting is a little easier.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Mick is right, the coil must match the system, or it won't last.
It's very easy to test if there is a resistor by using a multimeter set to volts.
Attatch multimeter black lead to ground, with coil + wire disconnected check the volts at the wire when ignition on. If it's close to 12v then there is no resistor.
I have had roundies and clubbys, only 1 clubby had a resistor and it was fitted aftermarket.
I have only ever known coil resistors to be a ceramic block about the size of a bic lighter with a terminal each end.

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Dean Hutton's first car was a Mini.

12V coils are 3 ohm resistance, `use with resistor' coils are 1.5 ohm.
A `resistor' coil is simply a coil rated for around 7V, the ballast resistor simply drops the normal 12V supply to this during normal running.

Later UK Minis had a pink resistor wire to the `use with resistor' coil, but no Oz Mini ever did.
If you want to use a resistor coil, just buy a 1.5 ohm ballast resistor from Supercrap etc and put it in series with the coil 12V supply.
But generally, a 12V one eg. Bosch GT40 will work fine.

If you run a resistor coil eg GT40-R with NO resistor, you will burn the points fast and overheat the coil which will give you problems.
The exception to this is when using electronic ignition, eg Pulsar dizzy conversion- these run best with a 1.5 ohm coil, some conversions use even less eg Pertronix II.

Ballast resistors came in to improve cold starting. Originally some cars eg Valiants used this with 2 ignition supply wires- a 12V supply that bypassed the resistor during cranking, and another that went through the resistor during running.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hey Doc, what sort of coil have you been running with your Petronix igniton? Come to think of it, Im still running a resistorless coil with my petronix, never changed it from when I had points....

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http://www.youtube.com/user/Hanras

Brad,
The Pertronix 1 is rated ONLY for a 12V coil, on 4 cylinder motors. See http://www.vintageperformance.com/retro ... /lucas.htm
However, you could use a 1.5 ohm coil WITH ballast resistor, as long as you provide a full 12V supply to the Ignitor (the red wire).

The Pertronix II new dizzy I bought recently uses any coil from 3 ohm down to 0.6 ohm. I bought a Flamethrower 0.6 ohm, 45KV one.
I'm not using this setup at the moment, but it's going on the 1412 stroker with RE13 cam, once GR has had a look at the advance curve.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc - the Pulsar conversion is the 1.5 ohm coil run with or without resistor?

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

without. It will work with a 3 ohm but gives less voltage.

with a GT40-R (1.5 ohm) it will fire the plugs at .040" gap.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I got a shock for mthe coil on the pulsar distributor I was running. It kicked my arse all over the garage! It's pretty good on a cold morning.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.