Misc: Ignition Lucas KVF Rebuild - UK Recommendations?

[oexing]

Last year I found a Bosch type quite similar to the SR , only manual a/r but for two plugs , by having a slip ring and brushes for distributor. They were planned for industrial engines, not motorbikes in postwar times. Tonight I change the old capacitor for the WIMA impulse cap just to look and see, no plan for a motorbike with it yet.
Wonder how a single mag can have two different flux positions , the rotor would need asymmetric iron cores - I doubt this. Sure, you could have an ATD on them - on the drive gear certainly, which I´d hate. The smaller Marelli in photo right side got automatic ATD on breaker end but only for singles like Guzzis or Gileras. But none would fit under the mag cowl on a Vincent.
Anyway, manual a/r or automatic, in all cases you want best flux position at fully retarded for kickstarts. So this is what I would look into for tricking it out somehow, don´t just know yet how to do this best, depending on the type of magneto you got.
Another photo shows the camshaft mounted Bosch mag on an Earles BMW, with a/r behind breaker. It is set up with best flux at fully retarded of course and a twin with 180 degrees ignition on the flat twin, no wider space between any TDCs on them for sure - and no valve lifter as well. You can see the best flux timing mark on the mag rotor and a vee on the brass case, set at fully retarded, automatic ATD in front for breaker only.

Vic

 

[stu spalding]

The SR1 only has one spark plug lead.

but it should accept the twin cylinder cap and cam, suitably modified. Cheers, Stu.

 

[Chris Launders]

The SR2 uses a single lead coil and distributor arrangement but you could have the coil wound for twin leads, or fit a hunt coil and just bring two leads out running a wasted spark system.
I have seen asymmetrical SRs, I have several in pieces so will have a look later, you used to be able to pick the 4 cylinder ones up very cheaply and pillage them.

 

[oexing]

Chris, when you can find the time, I´d be interested to see some photos of these asymmetric SR mags and some info about twin coil mods. Just I am not so positive that twin coils can be made to fit in there reasonably, the space is very limited. Bosch went the slip ring distributor way to have them suitable for twins. But then post war the time was over for magnetos and only on industrial engines they were used for a while when no battery was a matter for limiting the weight of the device like in fire fighting equipment or generators. In my country only the Earles BMW twins had serious magneto ignition postwar ending with the /5 series that got coil ignition and electro starter in 1969. So it is surprising that Lucas had still worked on the SR types deep into the 50ies obviously .

Vic

 

[Chris Launders]

Hi Vic
From the looks of it I have bits of one asymmetrical SR and 3 symmetrical ones, here are pictures showing the types with their rotors.
As for twin coil mods I don't know how they are done but Hunt and Morris mags have a twin output coil in place of the single output one in the top of the magneto (I can dig my Hunt magneto out and take pictures if you want as it's not fitted at the moment)

 

[Chris Launders]

Vic, if you want to play with the asymmetrical one I don't mind trying to sort out enough bits to complete it and send it to you, you would have to make a cam and get a twin spark coil but I think Hunt ones fit.

 

[oexing]

Thank you very much, Chris, never seen these asymmetric mags , both rotor plus case concerned to be asymmetric. I wonder what engines were meant to have them, some v-twins ? Or industrial as well ? To be open, just by looking at your photos I am unable to come to grips about the workings with these uneven gaps between rotor segments and then same applies to the gaps in the case . Well, not a big problem , I don´t have projects that would fit to that type of mag, just trying to learn a bit still - at 70 plus - same as you .
Last night I changed the capacitor in the Bosch twin spark type with slip rings for a new cap for playing a bit with the manual a/r for watching sparks at all positions. Actually the difference was not so obvious in both ends of range. Basically it should matter as maximum flux is set at defined gaps between rotor and iron segments in the case. I did not see big difference in sparks so maybe in your case with no or very poor sparks at full retarded there might be some fault by shorts somewhere at retarded ? I don´t remember, did you check for sparks at retarded - poor spark or nothing at all in that position ? But then, once the engine was started it was allright even with full retard you said ? So then it seems more likely that the spark at retarded is just very poor when kicking. So that might point to a shifted internal timing up to a position with poor flux way off best. Next question is then - how to correct. When it comes to this I am not qualified for Lucas types, got only a profoundly wrecked one from Argentina.
For Vincents the rotating magnet types will not fit under the mag cowl , so for many not an option. I´d go for coil ignition and distributor in those cases. The Vertex I found will basically not fit there and the engine case had some time on the mill for clearing the place to have the Vertex there. But then, that is me as most here know by now . . . .
Anyway, a good friend each time starts talking about electronic ignitions with selectable timing curves. But my standard comment is no, thanks, but no. I would not want to do the trip Paris to Bejing with electronics on board, same arguments why certified aircraft with piston engines all got two magnetos for twin spark cylinders - no electronics legal yet . I can fix most troubles in a magneto but am hopeless with electronics. But then, nobody can do, blackboxes are typically sealed for good.

Vic

 

[Chris Launders]

Hi Vic, I bought the asymmetrical magneto off Ebay, it was listed as an AJS/Matchless, but it obviously wasn't as it has an oval two hole flange mounting, probably industrial.
As for my "missing sparks" with the Brough it is a 60 degree Vee so the 2nd spark is 30 degrees late and then with manual retard is probably another 10+ so something over 40 degrees behind the maximum flux point by which time the charge in the windings will have decayed considerably, I don't think there's a magneto problem other than the actual physics of a V-twin mag.

I have before built a points set up with manual adv/ret by taking all the windings out of a magneto, fitting a single slip ring with a wire from this to the back of the magneto points, this provided the contact breaker for a twin spark coil feeding both cylinders, two wires from the coil going via a condenser and a copper core HT leads into the pickups.
Worked really well and of course looked exactly like a magneto fitted bike, the coil being hidden under the tank.

 

[Steve Marks]

Having the internal magneto timing at maximum strength only at full advance is a stupid idea: At poor kickstart speeds you need all voltage you can get from the mag so the internal timing shall be set for retarded position for maximum voltage. Once the engine has started the magneto is run at a lot higher speed , so it will produce healthy sparks anyway . So then the internal timing can be moved away from best position as it no longer matters so much. At least that is what we on the continent did for decades for having an engine capable for kicking it into life from a mag.
That idea with ATD in the drive gear may have its roots in the idea that it will not compromise the internal timing of the mag when the rotor and magnets will keep their timing no matter if advanced or retarded. But I have never come across magnetos on continental machines that got the ATD in the drive gear but instead got nice small ATDs on the breaker end, no troubles from this ever for long times. Just that you set best mag internal timing for max. voltage at full retarded as shown above.

Vic

Sounds a good idea but in practise, it cannot be done. The best spark in a magneto comes when the points open just after the magnetic break occurs and the magnetic field starts to collapse. That is arranged to happen when he ignition timing is fully advanced. When you manually retard the timing, the magnetic field has already collapsed for a while before the points open - hence the weaker spark when retarded. Now, you suggest setting the manual lever in the fully retarded position when the spark is at it's best. That will work but as soon as you manually advance the timing, the points will open earlier - before the magnetic field starts to collapse and as a result you won't get any spark at all!

 

[oexing]

No , Steve, it ain´t so. You want the very best position / timing in the magneto for retarded when the rotation speed is minimum. Otherwise you would not be able to produce a spark from kicking for starting the thing. Once the engine is live and the rotation speed a lot higher it will have nice sparks anyway, even with less than optimum positions of poles. Just try with a good magneto and change its internal timing when it can be done in some way.

Vic