Bosch Magneto

[Mark N]

Hello,

 

I would appreciate any advice to help me understand how I can ground this Bosch DU 4 magneto. I have the wire connected from the ground terminal on the magneto to a kill switch and then to the car frame. When I go to crank the car I can't get it to ground out the spark plugs. I cleaned up the ground connection on the car frame down to the metal for good contact and I cleaned the other connections as well, but no luck.

 

What am I doing wrong?

 

Any thoughts would be appreciated.

 

All the best,

 

Mark N

[F&J]

"When I go to crank the car I can't get it to ground out the spark plugs."

 

Do you mean that there is no spark to the plugs?

 

The yellow wire can be disconnected from the Mag and the Mag should produce spark, in case the switch or the yellow wire was being shorted out.   That yellow wire is to shut the engine off.

 

I'd clean the points really well, check the point gap, and disconnect the kill wire at the mag, then try the spark.  Pull all the plugs out, and lay them on the engine with wires on them, to test.  You can spin it faster that way.

 

The magnets could be weak, but I'd think you'd feel some zap if you held a bare wire

 

One more thing is that the bearings in the Mag are isolated from ground, with thin paper material around the bearings.  If someone had the mag apart and left that material off, it will be shorted out.

Edited March 13, 2016 by F&J (see edit history)

[Mark Shaw]

Clean the cap & spring clip to make sure it is also electrically connected to the Mag body.

[JV Puleo]

As F&J says, the connection from the points (the yellow wire) is to shut it off. It will never work if it is connected to ground.

I would check the point gap. They can close up (a problem I once had on the road). The high tension spark travels along the spring loaded rod that connects the little porcelain cover to the inside center of the cap.

 

That said, if this is an old mag, the condenser may well have failed, in which case it has to come completely apart. This isn't an easy job and it takes some special tools to do it without damaging some small parts. They work just fine until they fail and all original mags will fail eventually.

[Guest j.Illeney]

so it sounds like your car runs - could it be the kill switch ? does it ground out when it is touched to the frame direct ? 

[Mark N]

Thank you for the suggestions. Just to clarify, the magneto works and I get current and spark to the spark plugs. I just can't shut it off, it will not ground out. The yellow wire is connected to the kill switch and then to the car chassis. I will try and connect it directly to the chassis and bypass the kill switch to see if that is the problem. I was just wondering if I should be looking at something else as well.

 

Thanks again.

 

All the best,

 

Mark N.

[Dandy Dave]

Just under the cap the wire is hooked to there should be a flat spring with a "Button" on the end. It goes to the center and grounds out the points. Is it still there? Or has it been broken off at some point? Without a ground-able connection in the mag it will not shut off. Dandy Dave! 

Edited March 14, 2016 by Dandy Dave (see edit history)

[cahartley]

^ I was going to post the same thing.......