ET: Engine (Twin) Old Coil Ignition Points Identification

Monkeypants

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The rear 6 volt coil ends up getting fed with 3 volts when the gap is narrowed on both sets of points.
It's not enough to fire the plug.

Re the worn out parts comment-
The bike can be seen at 1:35 and 4.00 in Gerry's video of the 2007 IOM Vincent Lap.
This is about 20,000 miles after the 1 cylinder problem, but same ignition, same old Lucas points.
The bike had enough speed to pass 31 riders on the lap including five twins all lined up racing WFO, riders flat on the tank and doing over the ton on the Sulby Straight. A lovely Godet restored Black Shadow was leading the charge at about 115 mph by my speedo. Even managed to catch and pass him.
Would that be possible with a "clapped out" ignition?


Glen
 
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Bill Thomas

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It is noticeable that the cam profile on the multi cylinder aero mag is very short and lumpy, thus giving maximum dwell time regardless of point gap.

A typical coil will require 2.5 milliseconds to achieve a reasonable saturation in order to give a decent spark. At 4,000 RPM that equates to 60 degrees of crankshaft movement. With an unknown cam / points setup it is worth checking that this figure is attained, something that I suspect Stu, above, already knows.
A small point gap will increase dwell and, as Simon mentions, will waste electrical power and could overheat the coil. Charging past the saturation point has no advantage.
Talking of charging the condenser in the same context as dwell is not really correct. Dwell is when the points are closed. As one side of the condenser is connected to earth and the other is connected to the points the condenser is discharged during the dwell time. Its main function is to quench the voltage rise as the points open in order to prevent arcing and provide a clean break. The points must be open wide enough by the time that the condenser is charged so that they are then unable to arc. Too small a gap can lead to arcing and will give similar symptoms to a failed condenser.

I agree with Vic that if a reduced points gap, when measured static, is cutting one cylinder out then it is likely to be wear in a component causing the gap to be further reduced when under running conditions.

But hey, if decent points and a 25 thou gap fixes it then who cares?View attachment 28230
Hello Pete, Just fitted a "D" Distributor to Ron's Comet, With a very Pointy single cam, Don't know where it came from, 12 v, Starts well and goes well, Should I be worried about Coil failure. Cheers Bill.
 

Simon Dinsdale

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If I recall on Glen's bike when it had the small gap and running two sets of points on a 50 deg engine (as it was designed for a parallel twin) something about one set of points grounding thru the other when the one of the sets was supposed to be trying to deal with the coil, and that was why it went onto one cyl and why opening the gap to 25 thou let it function as god (and Lucas) intended. Certainly it was nothing to do with worn components!
That now explains what is occurring on Glen's bike. As it was originally a parallel twin unit I suspect one set of points has being moved to alter to 50 deg configuration. This could bring in the problem that Peter has described where the both points can be closed at the same time or more likely very close to that situation so the coil doesn't have enough time to fully saturate and so no spark on one cylinder. What is really required is a new cam profile, but by altering the gap to 25 thou gap it has altered the dwell angle enough to allow both cylinders to fire and overcome the problem.

Simon
 

erik

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On my early Commando I had nearly the same construction with atd unit behind the Points .It never worked properly and the atd unit never worked as it should.I converted to boyer electronic ignition and the Troubles were gone.enginine running smoother ,lower consumption of gasoline and no more Timing Troubles.It is in the bike for more than 25 years!!To my mind it is a part for a mummie in a Museum.Regards Erik
 

Monkeypants

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The ATD on this arrangement is different than the Commando.
I agree electronic ignitions can be excellent. Most important for any ignition is that doesn't leave you stranded roadside.
In 57,000 miles this ignition has only given me trouble once, self induced after fitting the expensive but low quality points, for the reason discussed. Even then I was not stranded, I just had to figure it out.
So I don't see this setup as something that is made wrong , should have a different cam profile, needs an " alterred gap" to overcome it's problems or has clapped out parts.
Most everything has a spec and the spec for the system is 25 thou gap. Then it works very well, you couldn't really ask for more from it.
The Electronic ignitions all seem to have their issues, Boyer quite often had the broken pick up wire problem. Boyer has lots of haters although I have had good luck with Boyer on Nortons.
Other Electronic ignitions will fry the black box now and then. Trispark is particularly well known for this.
Pazon might be the best of the bunch, but even those have the occasional failure.
With the points bike I now carry a complete spare ignition ( just 1 coil tho) and it's all pretty simple to work on roadside if it ever gives trouble.
My main goal was to help Rob ( the original poster) and maybe save him some grief, given that I have used that same ignition for so long now with only that one early issue.




Glen
 
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erik

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@ Glen : I agree with you that on the Norton twins there is boyer a satisfying solution.On my Comet I have the original magneto fitted with a nos atd unit.No Problems.When I started to restore my rapide there was only the half of a Pazon ignition with the bike and so I diceded to go the BTH way.I hope the bike is next week with TÜV and on the road, then I will see if this decision was a good idea. Erik
 

Nigel Spaxman

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I am trying to understand why Glens ignition doesn't work with .015 gap. The same ignition works with .015 gap on Triumphs, Nortons, and also the BSA and Triumph Triples. It guess the triple is like a vee twin with a 120 degree angle between the cylinders and a third cylinder added. You would almost think that you could add as many of these circuits as you wanted and it would still work.
I guess it must have to do with the dwell. When either set of points open that should cause a spark if the coil is charged. It may be though that the dwell is such with the .15" gap that just before the points open on the rear cylinder, or more or less simultaneously, the points close for the front one. When the front points close the condenser for the front cylinder is suddenly connected to the circuit, maybe that right at the worst possible time causes a drop in voltage to the other coil and condenser, and it discharges the other coil just before it needs to fire?
 

Monkeypants

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Nigel, its the voltage drop that occurs when both sets of points are closed while the rear 6 voltcoil is getting charged. With narrow gaps the voltage available is 3 volts.
With the proper gap the voltage is 6 v, as it needs to be.
John McDougall told me this early on, it took a few minutes of looking at it quietly to figure out why.
The prospect of riding a 1 cylinder Rapide for 400 miles through the mountains tends to focus the mind!

Glen
 

Peter Holmes

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For those of you that know how to use a slide rule, or even one of those new fangled electronic calculator things, I think Sinclair might make them, if I change my current points gap on my single Lucas distributer fitted to my D Comet from 12 thou to 15 thou, how much will it advance or retard my ignition timing, I have only had it set on 12 thou for the past 10 years because that was the figure in KTB.
 

Nigel Spaxman

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Peter I doubt you can figure out how much difference to the timing .003" of gap would make without knowing the shape of the cam that lifts the points. My guess would be that it the timing difference would be less than 5 degrees.

Glen, I had forgotten about the 6 volts and the voltage drop. On most of the other bikes with this system it is 12 volts so maybe there is less voltage drop. I think on the vertical twins the firing points being 360 degrees apart instead of 310 and 410 on the Vincent might help, maybe on those bikes there is never a time when both points are closed at once.
 
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