Magneto Trouble

[Mike Etson]

Hi,
My left cyl ignition just cut off today while riding and didnt come back. Tried another plug wire, and still no spark on the left side. Do magnetos fail like that? This one was replaced about 4 months ago with one of the plastic housed reproductions. I got it locally, I dont know if it originally came from Mark or not. Has anyone had similar problems? Are the original type better? I sure would appreciate any imput on this - thanks

[Allan Atherton]

I don't know much about this, but both spark plug wires go the single coil, and the magneto is on the other side of the coil electrically. Therefore I would think that neither the magneto nor the coil would make one side fire and not the other. I think the spark is not distributed to the plugs; rather both plugs get the same spark. (There must be twice as many sparks as one plug can use.)

Since you replaced the spark plug wire, try replacing the spark plug. One day my bike would not run on one side. There was no spark there, so I replaced the plug and that made it run. Then I remembered I had dropped that plug on the concrete floor once. The gap was not affected, but the fragile internal carbon conductor must have snapped. The spark plug worked OK for many days, then one day it stopped passing the current.

[Mike Etson]

Thanks for your input. I tried another plug too. There isn't any spark there at all. With the bike running on one cyl, I put a screw driver in the end of the wire, and held it close to the head to check for spark - none.
I wonder if half of the coil windings could short, so that only one pole sparks?
Mike

[rolf]

hallo,
I don"t know how these new coil work,but if it has the same wiring inside as the original the only fault can be the "Sicherheitsfunkenstrecke".You have between the srews for the ignitionwire and the magnetobody for each srew a metaltongue(?)on the body.This tongue should "catch" the spark if it is impossible for the spark to go over the plug to ground.Otherwise the isolation of the coil would be destroyed.
the gap between screw and "tongue" should be 11mm,if it is shorter(less 8mm), it is easier for the spark to go over the tongue as over the sparkplug.That could be the only reason for your trouble.Normaly, it is impossible that only one pole sparks,because of the inner building of the coil.I hope my silly english is good enough for explaining the "tongue" and so on.
Otherwise ,ask again and I will ask my dictionary.
rolf

[Mike Etson]

Hello Rolf,
I understand what you mean. I did check the safety pathway "tongues" for the coil, and no spark was jumping there. I set the gap at 10mm, and nothing is jumping. I too find it hard to understand how the coil could work on one pole but not another, but I cant think of any other possibility either. Does anybody else have any ideas?
Thanks,
Mike

[Mark Huggett]

Hi Mike, you are another victim to join thousands of others who have bought Taiwanese ignition coils. The black and the reddish brown plastic ignition coils are rubbish. The best ignition coils on the market are the rewound coils that we sell in exchange for the old carcasses. The second best coil is also a plastic cast coil which is grey in colour. We carry these in stock for the budget conscience client. They are, like all plastic repros, incorrectly wound for battery ignition instead of Magneto ignition, but they are robust and work just fine.

Best regards,

Mark
Mark Huggett GmbH

[Tom Hagan]

Mike,

A simple test would be to switch the spark plug wires at the coil. If the spark switches sides, then it is a bad coil. If not, then it is bad wire/cap/plug.

Tom

[Michele Varcasia]

Mark, which is the price of the rewound one, with an armature back ?
Michele

[JON KENT]

I fitted one of the plastic housed coils, covered in black plastic. I was told by the English dealer that these were high quality, and that the bad Taiwanese ones were covered in white plastic. Anyway, having fitted this new coil my starting is no better than with the old coil. Could it be that the magneto rotor has lost some of it's magnetism, and needs remagnetising?

[John Stanley]

I assume you fixed the problem by now. First of all I have no experience with BMW's, I am restoring my first one right now. since this is a "Wasted Spark" ignition system, I would assume that there is a single coil, and that each end of the secondary (high tension) runs to a plug. This type of system is how a twin lead harley coil is wired. The secondary circuit is completed by both plugs firing in series. that is the circuit runs from ground on one plug, jumps the gap, up the wire to coil, through the coil and down to fire the other plug to ground. This is different than having 2 coils in which each coil has one side of its secondary winding grounded to the metal case of the coil. To me I would suspect a short to ground on the end of the coil nearest the tap that does not work. Also when trying to fire one side of the coil for spark, be sure the other side is either on a plug, or better yet ground it. PS: if anyone is interested I have a site with my collection, including the R-50 I am currently restoring.