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I have just had the coil fail on my 1970 CP PI. Luckily it was close to home and my darling wife bought my TR touring kit down to me.

The coil in the car when I bought it failed about 3 years ago. When I replaced it I used the same coil as I use in my TR2 as I have a spare in my road touring kit.

The TR6 has Lumenition electronic ignition, the ballast resistor has been disconnected but otherwise a stock TR6.

What coil would owners recommend for the PI TR6 with electronic ignition. Would the TR2 one be OK.

Edited by John McCormack
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Hi John

I too have electronic ignition with my ballast resistor by-passed I use a Petronic flame thrower coil 3.0 ohm, Ive had this fitted for over 5 years and have done a couple of trips to Le Mans :D, with no issues 

 

75D59AAE-206D-4CA6-94AE-96CBD35AFB2A.jpeg

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Yes, they are both 12v coils. 6v coils, which use a ballast resister except when starting were introduced with the CR series in 1973.

My experience is that coils fail from time to time whether they be expensive with pretty labels or basic with no labels. Never spotted the difference in performance or reliability. I always carry a spare.

Mick

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Any decent make of 12 v coil would be suitable John so your one from the TR2 will work - the only question is for how long as there are stories of cheap modern 'far east' coils failing quickly. Two failures in three years is unusual I would think and may point to some common cause related to the car. What points gap are you using? If 30 thou or over you need to be using a 'sports' coil built for the higher voltage.

 The Distributor Doctor sells The Pertronix 'flamethrower' coils that Clarkey recommended (and which I also have) so they must be good and are surely available locally in Oz.  Bosch 'blue' coils are reputed to be OK - I believe those are made in South America now. 

 Though I note what Mick says above, my personal experience does not show the same failure pattern.  Perhaps I have just been lucky. 

 

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23 hours ago, RobH said:

Any decent make of 12 v coil would be suitable John so your one from the TR2 will work - the only question is for how long as there are stories of cheap modern 'far east' coils failing quickly. Two failures in three years is unusual I would think and may point to some common cause related to the car. What points gap are you using? If 30 thou or over you need to be using a 'sports' coil built for the higher voltage.

 The Distributor Doctor sells The Pertronix 'flamethrower' coils that Clarkey recommended (and which I also have) so they must be good and are surely available locally in Oz.  Bosch 'blue' coils are reputed to be OK - I believe those are made in South America now. 

 Though I note what Mick says above, my personal experience does not show the same failure pattern.  Perhaps I have just been lucky. 

 

Thanks Rob.

I have had a coil fail twice on my daily driver TR2. Not bad in 45 years but enough to carry a spare.

Plugs are gapped at 28 thou, 3 thou above the 25 recommended. No points.

The first coil that failed was on the car when I bought it and might have been any age, it wasn't near new. The one that failed yesterday was my TR2 spare, a Lucas sports coil. 

I'll get another one for the touring kit and see what happens.

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23 hours ago, Mick Forey said:

Yes, they are both 12v coils. 6v coils, which use a ballast resister except when starting were introduced with the CR series in 1973.

My experience is that coils fail from time to time whether they be expensive with pretty labels or basic with no labels. Never spotted the difference in performance or reliability. I always carry a spare.

Mick

Thanks Mick,

This car had/has a ballast resistor fitted, apparently from new. I have disconnected it as I have been told it isn't necessary nowadays. My knowledge of electrics is not high.

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48 minutes ago, John McCormack said:

This car had/has a ballast resistor fitted, apparently from new. I have disconnected it as I have been told it isn't necessary nowadays

The ballast resistor thing is pretty simple John.   When you start the car you need a good spark because the engine is stone cold, the oil is thick and the mixture rich - which is fine if the battery is tip-top but not if it is down a bit on charge and struggling to crank the engine.  

In order to ensure a good reliable starting spark, manufacturers started to fit coils designed for a lower voltage so that even if the battery voltage is a bit down, there will still be a decent spark.  Once started, however, the voltage rises to the usual level which would destroy the low-voltage coil, so it was necessary to connect it direct to supply only while cranking and to switch a 'ballast' resistor in series with the coil to drop the voltage again to a safe level once the engine is running.  

If the vehicle still has a low-voltage coil the ballast resistor is needed to prevent the coil overheating.  If the coil has been swapped for a 12v one, there is no need for the resistor and the coil should be connected direct to 12v from the ignition switch.

Whether there is any benefit from a ballasted coil  nowadays is debatable as it will depend on such things as the prevailing climate where you live, whether you use the car during the winter, and what engine oil you use.

Edited by RobH
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On 9/18/2020 at 8:56 AM, RobH said:

Any decent make of 12 v coil would be suitable John so your one from the TR2 will work - the only question is for how long as there are stories of cheap modern 'far east' coils failing quickly. Two failures in three years is unusual I would think and may point to some common cause related to the car. What points gap are you using? If 30 thou or over you need to be using a 'sports' coil built for the higher voltage.

 The Distributor Doctor sells The Pertronix 'flamethrower' coils that Clarkey recommended (and which I also have) so they must be good and are surely available locally in Oz.  Bosch 'blue' coils are reputed to be OK - I believe those are made in South America now. 

 Though I note what Mick says above, my personal experience does not show the same failure pattern.  Perhaps I have just been lucky. 

 

Yep the red Bosch coil I recently got was made in Brazil.

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My Lucas gold failed last year after 25 years. Couldn’t find the receipt.

The current Lucas gold ones seemed a bit cheapo in terms of feel. The consensus on here was Bosch blue. At least with Bosch you are getting a major brand with a good reputation.

Many of the others seem to be generics with no real track record of longevity and plenty with fancy sounding names implying magnificent performance. Given they all work by generating a high voltage spark in the ht circuit induced by the points opening in the LT circuit, the reality is the performance is limited - a 3 ohm coil operating at 12v is only going to generate a certain spark energy so ultimately what is important is reliability.

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11 hours ago, RobH said:

The ballast resistor thing is pretty simple John.   When you start the car you need a good spark because the engine is stone cold, the oil is thick and the mixture rich - which is fine if the battery is tip-top but not if it is down a bit on charge and struggling to crank the engine.  

In order to ensure a good reliable starting spark, manufacturers started to fit coils designed for a lower voltage so that even if the battery voltage is a bit down, there will still be a decent spark.  Once started, however, the voltage rises to the usual level which would destroy the low-voltage coil, so it was necessary to connect it direct to supply only while cranking and to switch a 'ballast' resistor in series with the coil to drop the voltage again to a safe level once the engine is running.  

If the vehicle still has a low-voltage coil the ballast resistor is needed to prevent the coil overheating.  If the coil has been swapped for a 12v one, there is no need for the resistor and the coil should be connected direct to 12v from the ignition switch.

Whether there is any benefit from a ballasted coil  nowadays is debatable as it will depend on such things as the prevailing climate where you live, whether you use the car during the winter, and what engine oil you use.

Good explanation Rob, quite a few people don't understand the ballast ignition system and I've seen at least a couple of 12v (3ohm) coils fitted to later TR6's because the owners assumed they would get a better spark.

I believe my car is ballasted (1973) but I've never found the resistor, I guess its in the harness somewhere.

Bob

Bob

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9 minutes ago, OldBob said:

I believe my car is ballasted (1973) but I've never found the resistor, I guess its in the harness somewhere.

Yes that's right  Bob - it is a length of resistive wire within the loom itself rather than a discrete resistor.  

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23 hours ago, RobH said:

The ballast resistor thing is pretty simple John.   When you start the car you need a good spark because the engine is stone cold, the oil is thick and the mixture rich - which is fine if the battery is tip-top but not if it is down a bit on charge and struggling to crank the engine.  

In order to ensure a good reliable starting spark, manufacturers started to fit coils designed for a lower voltage so that even if the battery voltage is a bit down, there will still be a decent spark.  Once started, however, the voltage rises to the usual level which would destroy the low-voltage coil, so it was necessary to connect it direct to supply only while cranking and to switch a 'ballast' resistor in series with the coil to drop the voltage again to a safe level once the engine is running.  

If the vehicle still has a low-voltage coil the ballast resistor is needed to prevent the coil overheating.  If the coil has been swapped for a 12v one, there is no need for the resistor and the coil should be connected direct to 12v from the ignition switch.

Whether there is any benefit from a ballasted coil  nowadays is debatable as it will depend on such things as the prevailing climate where you live, whether you use the car during the winter, and what engine oil you use.

Thanks Rob. That is what I understood about ballast resistors but not well enough to articulate it like you have.

I'm in Sydney Australia so it is rarely cold enough to cause a starting problem. It might be if I needed to start at 6.00am in the middle of winter but I'm retired and not a morning person.

The car starts first thing all the time, except when the coil is u/s.

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Hi John,

Not sure what a Bosch Blue is here in Oz but I have a Bosch GT40 fitted to my 1971 TR6 (no ballast resistor). I believe the GT40R would be suitable for a ballast-resistor installation, although you'd best check as i think it's a 9V coil and my manual says the CR-series TR6 had a 6V coil. What year is your car? More importantly, what year is the loom? The CP-series have a white lead powering the coil, whereas the ones with a ballast resistor have a  white/yellow lead. If you know you have bypassed the BR then no problem.

John

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19 hours ago, JohnC said:

Hi John,

Not sure what a Bosch Blue is here in Oz but I have a Bosch GT40 fitted to my 1971 TR6 (no ballast resistor). I believe the GT40R would be suitable for a ballast-resistor installation, although you'd best check as i think it's a 9V coil and my manual says the CR-series TR6 had a 6V coil. What year is your car? More importantly, what year is the loom? The CP-series have a white lead powering the coil, whereas the ones with a ballast resistor have a  white/yellow lead. If you know you have bypassed the BR then no problem.

John

Hi John,

Mine is CP51049, a Feb 70 car, and has a white lead to the coil from the loom. It is essentially a survivor car with relatively low miles that has been repainted but not restored.

The car has Lumenition ignition and has a ballast resistor fitted, which I disconnected. I don't know why it is there, I thought it was original but it appears it isn't. 

Edited by John McCormack
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Martin, Distributor Doctor also sells some Indian made classic coils that he highly recommends.

Stuart.

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On 9/18/2020 at 8:29 AM, Mick Forey said:

Yes, they are both 12v coils. 6v coils, which use a ballast resister except when starting were introduced with the CR series in 1973.

My experience is that coils fail from time to time whether they be expensive with pretty labels or basic with no labels. Never spotted the difference in performance or reliability. I always carry a spare.

Mick

Hi Mick,

Just a small technical point, TR's post 73 do not use a ballast but a resistive wire which does the same thing. It is the pink/white wire in the cable harness!

Bruce. 

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