Some analysis of ignition problems please.

[davidf]

With Accuspark, Bosch red coil and ballast resistor, I was getting occasional light misfire at moderate revs and increase in throttle. But this was not all the time - for example, on the run up to the Silverstone Classic from home in Bournemouth, no issues. On the run home, it played up for a little while (lumpy slow acceleration from 70), then was Ok again. On Friday, it got a lot worse while I was out, very rough running, eventually stopped and would not restart. Not in a good place to work on the car, so got recovered home.
I test my ignition with an old-fashioned timing light, which has no external power supply; it has a red discharge light and it connects with 2 leads directly into a plug supply. If it flashes brightly, I have a good spark. Its leads are long enough to place it in front of the windscreen so I can see it when I am turning the ignition key to start.
Turning the engine on starter with timing light on no 2 plug - no flash
Then tested with one lead on a spare plug fastened with a cable tie to the front lifting eye, and one end in different places. First at the coil king lead socket - good flash. Then on the other end of the king lead - nothing. So, fitted an old spare king lead, car started instantly, ran smoothly, great. Plug lead set was 'green leads' from JP in 2014 - done about 11,000 miles.
Left it running to warm up and went in the house. Came out a few minutes later - it had stopped and would not re-start.
Went through a load of tests again, got to the point where the light showed a strong flash when connected between no 2 plug lead and the spare plug on the lifting eye, but only a weak flash when connected to no 2 plug. Swapped the plugs just to check, but still good on external, not on the one in the engine.
Now running out of ideas - tried a spare Accuspark - no different. Tried a spare distributor with points - no different.
Tried a spare coil (an old Lumenition one - previously discarded because it seemed to misfire when hot) - strong flash from the timing light on no 2 plug and the engine starts and runs OK. Hooray again, till the next problem turns up!!
I have had a history of coils appearing to give a light misfire under load when hot - proven by swapping quickly for a spare cold one from the boot.
Now, I have had a king lead fail, and within five minutes of replacing it, a Bosch coil fail (but only a 'marginal' failure because it will still generate a spark if the plug is not in the engine).
I have had similar light misfire problems with a Lumenition system (that was not the classic total cut-out from the 3 pin plug problem).

Any ideas what is behind all these ignition component failures?

By the way, I have a collection of different distributor caps and rotor arms - none of those behave differently. Once before when trying to chase down the problem I swapped the points and Accuspark between the 2 distributors - again no difference. I have recently fitted new plugs, but the old one behaved exactly the same in tests this weekend. All plugs gapped at 25 thou.
I will also post on Facebook Triumph Stag Fan Club, so those of you on there don’t need to reply twice.

[Lingen]

David.
There are regular reports on here of various ignition/electrical components failing early in their life. You seem to have had them all at once! Of all the components that come from "You know where" these days, the electrical ones seem to be the most troublesome (=useless). The problem is trying to separate the good from the bad, as the maker's name rarely means anything these days. Perhaps the best we can do is to let people know when it happens, as you have.
Mike.

[Mark S]

Same story, thought I had cured it with a new rotor arm and cap but its back. Different coils, pertronics, new leads, I've just bought a "genuine" Lucas distributor cap from a motor factor so will see...

[trunt]

When I was initially setting up my timing I could get it correct at 12 deg BTDC but it was at the extreme of the dizzy adjustment. One other thing that was bothering me was that initially when the engine was at TDC or even at 12 degrees BTDC the rotor did not point directly to the #2 contact in the rotor cap, it was pointing somewhere in between the two. Not sure how the engine ran but it did. (In the end I slipped the dizzy gear a tooth and it came in perfectly)
When I hear of such issues as yours I wonder if the rotor is pointing directly at the contact? Maybe it’s worth a check?

[davidf]

Yes, checked that, the rotor arm points to the no 2 lead.

[Lingen]

Nothing to do with component quality, but I have seen instances of where the bonding of the rubber between the two parts of the crankshaft damper/pulley has failed, so the timing mark is no longer in the right place for TDC.
The simple way to check this is to remove No2 plug, put a long screwdriver down on to the piston, and then turn the crankshaft till it reaches its highest point, and check the line against the vernier.
Mike.

[davidf]

Sure, but what I am after is some explanation for the HT components failing in sequence. I think if the timing was out, I would feel that when the engine is running (and by the way, I took off one cam cover to confirm the cam is still aligned with the crank). I don't think that an error in timing, small enough to allow normal running, would be a cause of HT component failure?

[NeilR]

With electronic ignition, IMHO, you don't need a ballasted coil.
Just fit a 3 OHM coil and dispense with the ballast resistor / wire.

I've been running like that for 15 years now & only had 1 failure - a Powerspark module that gave a misfire at revs.

[Wheelz]

With electronic ignition, IMHO, you don't need a ballasted coil.
Just fit a 3 OHM coil and dispense with the ballast resistor / wire.

I've been running like that for 15 years now & only had 1 failure - a Powerspark module that gave a misfire at revs.

Why dispense with something that degrades rather than improves?

[Wheelz]

Davidf. How sure are you that the problem is not on the LT side of the ignition?

[sujitroy]

Judt Fyi. Pertronix does not recommend their brand of 3 ohm coil for 8 cylinder engines. I have a Pertronx points in one Stag and have used their 1.5 ohm coil. they recommend doing away with the ballast.

[davidf]

Davidf. How sure are you that the problem is not on the LT side of the ignition?

Because changing the Accuspark module, and then changing the complete distributor for one with points, made no difference. Also, one test I did a few months ago was to measure the voltage drop on the ballast +ve when grounding the coil -ve - it was about 1.2V, which is lost with the current passing through the old wiring looms and ignition switch. I have fitted a relay to deliver power directly to the ballast +ve, triggered from the 'normal' ignition feed. It now keeps a constant voltage on the ballast +ve. Also, the coil end of the white/pink connection (from ballast -ve to coil +ve) looked very flaky, so I have installed a new lead for that connection. The ballast itself is quite new, and with the coil -ve grounded, I have a sensible voltage at the coil +ve (can't remember what it was but it was around 6V).

[davidf]

Judt Fyi. Pertronix does not recommend their brand of 3 ohm coil for 8 cylinder engines. I have a Pertronx points in one Stag and have used their 1.5 ohm coil. they recommend doing away with the ballast.

Interesting point about the (now deceased) Bosch red coil - on its label, it states that it must be used with a ballast resistor, or with electronic ignition. I have not got an oscilloscope (although I am thinking of buying one of the hand-helds that are advertised for around £50) so I don't know what the LT waveform looks like, but I always understood that electronic was supposed to give a sharper cut-off of current at the 'break', which induces a higher HT voltage. So it seems odd to have this comment on the coil label. The other concern is that there are so many different types of electronic, one wonders whether the thing in my car matches their idea of electronic ignition. So, I have left the ballast resistor in for fear of frying the coil. How could this cause a failure of the king lead, and then 5 minutes after fitting a spare one, a failure of the coil?

[DJT]

Dave, FYI I have been using a Bosch Red 0221119030 coil for 2 years (>7,000 miles) mounted in the original position. This is coupled to Pertronix ignition fitted by the Distributor Doctor when he overhauled my dizzy. Original ballast wire is still fitted and connected. NGK BP5ES plugs. Dizzy cap, rotor and vacuum unit were also supplied by DD. HT leads were also replaced (LD Parts), but I found that the resistance in some was considerably higher than others. I used most of the new ones, but used some of the older ones to get a matched set.

At the risk of jinxing things, everything is working as it should.

I did have an issue a few years ago when the car died on me. It turned out to be the ballast wire had broken inside its insulation where it is crimped/soldered to the coil connection. I cut the insulation back a few mm and fitted a new connector. I did piggy back the system with a Mk1 type ballast resistor, ready to connect up if it failed again, but that hasn't been necessary.

[Wheelz]

Because changing the Accuspark module, and then changing the complete distributor for one with points, made no difference. Also, one test I did a few months ago was to measure the voltage drop on the ballast +ve when grounding the coil -ve - it was about 1.2V, which is lost with the current passing through the old wiring looms and ignition switch. I have fitted a relay to deliver power directly to the ballast +ve, triggered from the 'normal' ignition feed. It now keeps a constant voltage on the ballast +ve. Also, the coil end of the white/pink connection (from ballast -ve to coil +ve) looked very flaky, so I have installed a new lead for that connection. The ballast itself is quite new, and with the coil -ve grounded, I have a sensible voltage at the coil +ve (can't remember what it was but it was around 6V).

From your original description of the symptoms, all the hallmarks of your problems seem to relate to intermittent operation, which I imagine could be due to intermittent power feed to the LT circuit. Just as an example, a dodgy ignition switch, or relay, or connector in the ignition circuit could cause a temporary loss of power.