Misc: Ignition Lucas KVF Rebuild - UK Recommendations?

[Chris Launders]

From my point of view the windings will be charging up all the time the pole is under the magnet and will stop charging virtually the instant the pole emerges from underneath, the spark is caused by the rapid collapse of the field when the secondary circuit is open circuited by the points.
This is when you will get maximum spark, any further and the voltage in the winding will start decaying and therefore the back EMF produced will be less.
In a dynamo or alternator if the armature has been skimmed the resultant larger air gap considerably lessens the units effectiveness so I would assume a similar thing applies to when the armature pole comes from under the magnet in a magneto, ie more than a few thou past and voltage decay sets in

 

[Cyborg]

Very nice setup. Now you need to add a pressurized container around the spark plugs, to simulate the combustion chamber.

Maybe I could use an old lawn mower engine with a Colortune stuffed into it?

 

[Cyborg]

So would the optimum setting be the same at 200 ( or less) rpm vs 2500 rpm? If so, maybe the lower rpm would allow someone with an oscilloscope to decipher what’s going on.

 

[oexing]

Chris, look at my 3 photos in the previous page. The first got the Bosch markings on rotor plus the vee on the brass plate for aligning when assembling the lot on the camshaft. This is the retarded position and internal timing of the magneto. So when you look at the second photo you can see same position from behind and the "stretch" of field lines by up to 11mm for retarded when the magnet pole piece has passed the iron block by a big amount. As there is an A/R device on the breaker end with advanced logically that 11 mm gap will become less by 15 degrees (30 degrees on crank), so only around 5mm remain at advanced.
When the atd is on the drive gear you´d have same retarded position as in photo no. 2 , speeds don´t matter, the internal timing in the mag remains fixed. Only with atd on breaker end the gap reduces with speed by centrifugal weights in the atd.
You can do tests with pressurized spark plugs, for plug testing or coil testing, does not deal with timing.
The big thing with magnetos in racing was always the higher the speeds the higher the voltage produced. Not so with battery coil ignition.

Vic

 

[Cyborg]

So would the optimum setting be the same at 200 ( or less) rpm vs 2500 rpm? If so, maybe the lower rpm would allow someone with an oscilloscope to decipher what’s going on.

The answer to that question would be no.