22 replies to this topic

[daenesh]

ah ok now i get what you're saying ..thanks

[StevieH]

Hello

 

First post on here.

 

After spending many hours reading about this ballast resistor business I need some advice.

 

I've recently come to the end of a very long mini restoration. Very long mainly because i didn't have the foggiest when i started!

 

Ten years on i'm almost there and now the real fun starts. Shes's now road legal and has covered only 60 miles.

 

Now to my issue. 

 

The original loom is from a 1985 998 Mayfair, which indicates it was a Ballast resisted system.

 

During the early days of trying to get her running, one of the wires in the engine bay melted. Which I replaced with a standard cable. (now i understand this was the ballast wire)

 

Taking in mind i knew nothing about the ballast resistor system at the time i bought a 12v coil lucas sports coil.

 

This lasted about 30 miles, then i had a points failure during the first MOT. Which resulted in the points, condesor and rotar arm being replaced. 

 

During this the garage burnt out the lucas coil and fitted my old coil and she ran! However 30 miles later this has now ceased to work- obviously due to it being a ballast coil.

 

Do i resort back to my 12v coil (Mulitmeter indicates a 12v feed from the fuse box)

 

or fit one of these?

 

http://compare.ebay....&ff14=66&ff19=0

 

Cheers!

[StevieH]

I tell a lie i have posted before! How embarrassing that I'd forgot and it was also about ignition!! Over two years ago!

[dklawson]

WIthout a path to earth through the coil... all your wires are going to measure 12V regardless of ballast or standard ignition.  To make meaningful voltage measurements in ignition systems current must be flowing (i.e. The points must appear closed). 

 

Since you have a points distributor and a multimeter the tests for which coil you have and what you need are easy.

1. Mark and remove all wires from the coil.  
2. Set your meter to measure Ohms and take a reading across the coil's low tension terminals.  Allow the meter 30 seconds or so to stabilizer.  Write that resistance value down.  Now touch the meter's probes together and wait another 30 seconds.  If the second value is NOT zero then your meter's probes have resistance.  Subtract that value from the one you wrote down for the coil resistance. 
3. Replace the wires on the coil.
4. Now remove the distributor cap and place a coin between the points.  Set your meter to measure DC volts and turn the ignition key to the run position.
5. Measure the voltage between coil (+) and earth.
6. Measure the voltage between coil (-) and earth.
7. Turn off the ignition, remove the coin, replace the dizzy cap.

If your coil measures between 1 Ohm and 2 Ohms, you have a ballast ignition coil and you need a ballast resistor to limit current flow through the system.  (Or of course... you could convert the wiring).

If your coil measures approximately 3 Ohms, you have a standard coil and you do not want a ballast resistor in the circuit.

 

Now turn your attention to the voltage readings.  

If you found 12V on coil (+) and zero volts on coil (-), you have a standard ignition system wiring and you need a 3 Ohm coil.

If you found 6V to 9V on coil (+) and zero volts on coil (-) then you have ballast ignition system and you need a ballast coil that measures between 1 Ohm to 2 Ohms.

If during these tests you found 12V on coil (-)... then something is wrong with the earth path inside your distributor.  

 

If you use a standard 3 Ohm coil on a ballast ignition system your engine will have a weak spark and may have trouble starting.

If you use a ballast coil without a ballast resistor (a ballast coil with standard wiring) then the system will allow too much current to flow and your points, condenser, and coil will all fail prematurely.

 

Make a few measurements and post back with your findings and I am sure you will receive lots of recommendations for what to do.

 

There is one other item to raise regarding points ignition systems.  Early dizzys like the 25D require that you apply a lubricant (grease) to the 4-lobe cam that opens and closes the points.  If you don't lube that cam the heel block on the points wears quickly and the points close up making it impossible for the engine to run.  On later distributors like the 45D there is often a felt wick supplied with the points.  This must be soaked with oil and positioned so it rubs against the 4-lobe cam that opens the points.  The oil wick takes the place of the grease used on the 25 series distributors.  No lube = short points life.

[StevieH]

Many thanks for the response. I will investigate this evening!

[Cooperman]

Excellent post, Doug, very explanatory.

And welcome back. I guess you are as pleased as the rest of us that 'his nibs' has now gone from here  .

[StevieH]

Many thanks Doug!

 

Followed your steps exactly how you said and it confirms i have a 12v system non ballast.. Went through the spare coils and confirmed which ones were which and selected the Lucas 12v non ballast sports coil (which still works).

 

However still no joy. So I lubricated the rotar cam and in doing so realised the points were shut when the major part of the lobe was acting on the points mech. 

 

Re set the gap and she started first time. 

 

Absolute belter of an evening taking her for her first proper legal run!

 

How and why did the points move?? Will this be a regular thing?

 

Regards

 

Stevie

[dklawson]

 

How and why did the points move?? Will this be a regular thing?

 

 

 

I'm glad you got things sorted out and that the engine ran well for you.

 

Regarding your question about the points closing up... yes... they are going to close up.  However, see the last paragraph of my last post.  Lubrication of the dizzy cam lobe is critical to slowing the wear and closing of the points.  There are also some junk parts out there.  I cannot advise you which brands of points are "good" and last longer.  However, once you find a set of points that seem to last... keep them.  You can file/dress points flat and re-use them several times before they have to be replaced.