Dual points for R69S (or any twin with magneto ignition)

[101-Scout]

I'm trying to obtain information and advice on setting-up dual point ignition to replace the single point standard ignition timing. One benefit, as I understand, is to eliminate the "differential timing" experience that can be evident for various reasons with these early model BMW twins.
Please see pic below.

I have seen this picture of a very tidy dual point layout and configuration. I am unaware of the author. Perhaps someone previously posted this on this forum?
Any help or contact with original designs much appreciated.
Also I welcome any feedback on dual points to rectify timing discrepancies between L & R cylinders.

Doug

[schrader7032]

Looks like an adaption of the Pentacomm plate. The Pentacomm had only one set of points, but the gap was adjustable with the running engine.

[niall4473]

Surely you would need two discrete coils, and therefore the original magneto would be no use except as a points carrier, the one in that blokes hand has the original double ended coil still on, I cannot see how it could work.

[schrader7032]

Why would you need separate coils? 8-cylinder engines run on just one coil. Whenever both points are closed, power is running through coil to saturate the field. The issue could be that the points aren't closed long enough to full saturate the coil.

Then there's the issue with the magneto and how it works. The magneto only provides maximum output at the "abrisz" point. I wonder how that timing works in this situation.

[101-Scout]

If someone knows of the designer/owner of this dual point setup image or any feedback on its actual running, especially to eliminate spark "timing differences" between the two cylinders that would of great benefit.
My understanding, is that with standard magneto ignition setup the single point open and spark fires to both plugs every revolution of camshaft. Please correct me if not the case.

The design benefit of this setup, is with two sets of points one designated for each cylinder, therefore timing of spark could be set precisely and independently for each cylinder.

I would like to contact this person who has made this with intention to communicate his/her experience.
Anybody used or know of such?

[101-Scout]

Correction: standard setup fires twice (once on each of those two timing lobes) to both cylinders simultaneously per rev of camshaft.

So, after further discussion:
with dual points, I would need modification to cater for extra set of points firing only at the correct phase of 4 stroke
Perhaps - single timing cam or ???
Any thoughts appreciated.

[niall4473]

Schrader,
the 8-cylinder engines you refer to have a single set of points and a distributor, this set-up would be the other way around almost, two sets of points in series, on the primary winding of a single coil, if we were talking about a 180 degree twin, it might just work, but on a boxer or a 360 parallel twin, (Triumph, Norton, BSA, etc.) both sets of points would be opening almost, or actually, simultaneously, it would run, given that the coil would spark both plugs when the leading set of points open, but there would be no differential timing (which is the object), and therefore no point to it, the lagging set of points would do nothing, except wear out.
However, if two separate coils were used, it could be achieved.

[Daves79x]

Differential timing is not that hard to overcome - just sayin'.

Dave

[wa1nca]

Schrader,
the 8-cylinder engines you refer to have a single set of points and a distributor, this set-up would be the other way around almost, two sets of points in series, on the primary winding of a single coil, if we were talking about a 180 degree twin, it might just work, but on a boxer or a 360 parallel twin, (Triumph, Norton, BSA, etc.) both sets of points would be opening almost, or actually, simultaneously, it would run, given that the coil would spark both plugs when the leading set of points open, but there would be no differential timing (which is the object), and therefore no point to it, the lagging set of points would do nothing, except wear out.
However, if two separate coils were used, it could be achieved.

Yes 2 coils would be needed
When the 1st set of points open 1st coil would fire off of one lobe of the advance
Then when the 2nd set of points open 2nd coil would fire off the other lobe of the advance

Any differential timing could now be offset by changing the gap slightly on one set of points

[johnlacko]

I’ve never been good at dimensional analysis, so pardon the dumb (if sincere) question, but wouldn’t the 2nd set of points be in the wrong position to fire the spark of the 2nd cylinder? Seems like having a cam lobe opening a valve 180 degrees too soon/late. To my mind, the only way I see this working is if there were two stacked cam lobes, each only engaging one set of points. For that matter, I can understand why you might use a dial indicator to find TDC verses trusting the flywheel timing mark, but once found, what problem is the second set of points really fixing? Both pistons are always in the same place relative to each other.

Inquiring minds want to know.