Just thought I should repeat this and
I should add that the proof of this occured on the BT-H test rig at 7000 (14000 engine) rpm
revs and at the minimum spark speed as well (Eddie can say what that is) bright it was not. but effective it sure is
Poor starting on new Amal and BTH Magneto
- Thread starter minivin
- Start date
I should add that the proof of this occured on the BT-H test rig at 7000 (14000 engine) rpm
revs and at the minimum spark speed as well (Eddie can say what that is) bright it was not. but effective it sure is
No. The process is identical at the wider gap. A wider gap requires a higher voltage, but the important thing is the electric field. That's Voltage/gap, so is about the same in both cases. The difference is a wider gap allows a larger initial flame channel to form (called the "kernel" in the combustion literature), which not only is more robust but also helps ensure complete combustion. Both are essential for meeting emissions standards. The reason a magneto needs a gap of only 0.018" is because the generated voltage increases directly with rotation speed, and the kickover speed is sufficiently low that not enough voltage is generated to jump a wider gap. If once underway you could reach into your engine and increase the gap to, say, 0.030", that would be better.
Any spark that will jump a a gap will burn holes in paper, so this "test" doesn't indicate anything.
p.s. take a look at the following "paper test" I did with a magneto I rebuilt. It didn't just put a tiny hole in the paper, it set fire to it:
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=462761#Post462761
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So to put this into a context which most of us can use; can I assume that if I test a spark system with my variable gap tester and the spark will jump an inch then that will be 'better' than a spark which will only jump a tenth of an inch, both at atmospheric pressure?
The answer is an definitive "sort of, but..." If a system is designed to provide sufficient voltage to jump the gap within a cylinder under compression (plus a bit more, just to be safe), more voltage than that is essentially wasted. What is needed at that point is current, since the energy dumped into the spark to create the shock wave is current x voltage integrated over the length of the spark.
A mistake some people who wind coils make is to use even finer wire for the secondary than is normally used, and to cram as many turns into the space available as possible. Such a coil might be capable of generating 60,000 Volts, except as soon as the voltage across the plug exceeds ~4000 Volts it sparks which effectively shorts the output of the coil and keeps it from rising further. At that point the quality needed from the coil is to provide as much current as possible over the next ~10 microseconds, since that's what maximizes the energy into the shock wave.
Wow ! Magnetoman is a real craftsman and details his craft marvelously . Superb writing , must be a teacher of some similar
technique .
Back to the Hamon system . If only jumping a normal plug gap it does not seem unusual , but if the distance is increased the spark becomes a lightning bolt searching for a ground in a hungry fashion . In a word fearsome . Have you seen Herves device ? Sid .
technique .
Back to the Hamon system . If only jumping a normal plug gap it does not seem unusual , but if the distance is increased the spark becomes a lightning bolt searching for a ground in a hungry fashion . In a word fearsome . Have you seen Herves device ? Sid .
This is all over my head as some of the equipment came about long after my experience with Vincents. They make repro side floats now? Were they not upgraded for a reason? Personally I would never use one for a serious road machine back when originals were easily available.
I know nothing of this twin plug magneto spoken about.... but that "good ground" posting made a lot of sense. I have used coil fired dual plugs on a twin.... but the optimum full advance has to be found according to the efficiency of your combustion chamber and how it is fed. As I remember 25 degrees full advance comes to mind. But what baffles me is the use of 1930's carb technology.
I know nothing of this twin plug magneto spoken about.... but that "good ground" posting made a lot of sense. I have used coil fired dual plugs on a twin.... but the optimum full advance has to be found according to the efficiency of your combustion chamber and how it is fed. As I remember 25 degrees full advance comes to mind. But what baffles me is the use of 1930's carb technology.
First, thanks for the compliment.
No, I haven't studied Herve's device. A properly rebuilt magneto is quite reliable and does a fine job sparking an old bike, so I prefer to stick with them. I have modern bikes that give me electronic ignition, fuel injection, and electric starting, all of which are great, but I like the old bike ridiing experience on an old bike.
Sidney,
You are quite welcome for the complement.... I said it because it is true.
As you know, I rebuilt Lucas magnetos usually finding the main problem with the old condensers, which, believe it or not, would go bad unused N.O.S still in the original box and packing. I replaced them with modern ones. Sometimes you would run into a bad winding and have
the armature rewound using wire with modern insulation. The Lucas Mag works fine. People bad mouth it but give no credit to the fact that is wonderfully compact and can fit about anything of the age. Poor Joe gets a bad name because he built exactly what the motorcycle
companies demanded: cheap. Oh name the day when a buyer from any Brit bike company came and asked for the best dimmer switch Lucas could provide? So, you are right again! A Lucas mag worked fine.... and if it didn't you could fix it.
You are quite welcome for the complement.... I said it because it is true.
As you know, I rebuilt Lucas magnetos usually finding the main problem with the old condensers, which, believe it or not, would go bad unused N.O.S still in the original box and packing. I replaced them with modern ones. Sometimes you would run into a bad winding and have
the armature rewound using wire with modern insulation. The Lucas Mag works fine. People bad mouth it but give no credit to the fact that is wonderfully compact and can fit about anything of the age. Poor Joe gets a bad name because he built exactly what the motorcycle
companies demanded: cheap. Oh name the day when a buyer from any Brit bike company came and asked for the best dimmer switch Lucas could provide? So, you are right again! A Lucas mag worked fine.... and if it didn't you could fix it.
See the following for the reason why this is the case:
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=466579#Post466579