Magneto help - Donny & Bigdog

Fri Jul 30, 2004 9:40 am

I finally received the parts yesterday. I tried to reassemble the J4 Mag. last night but got confused. I think that I am missing some parts. The coil had been removed so I have nothing for reference.

I order a new cap and coil but it looks like I also need a coil core, clips, srews & wedges. Is that correct? I see the hole that the coli lead feeds throuhg but what does it connect to? The terminal screw along with the condenser?

Sorry about so many dump question but it makes me mad when I can't seem to understand something so simple. Could someone start at the beggining and tell me the flow of the current? How does it get from the spinning rotor to the spark plugs?

I would love to get a handle on this before my head explodes!

Fri Jul 30, 2004 10:24 am

Ken, Your magneto coil is actually a transformer. The magneto generates electricity by spinning a rotor within a magnetic field. The magnetic field induces a current into the primary side of the coil (low voltage) Since the primary and secondary coils are wrapped together, this produces a current flow in the secondary. The primary coil is a few turns of heavier guage wire, the secondary winding is many turns of fine wire. This magnifies the voltage created. Controlling the primary side, contols the secondary side. There are 2 separate circuits to consider. First, on the primary side, the winding is connected to the points. The making and breaking of the points turns the current flow off & on within the primary side of the coil. Like turning a switch off & on. The energy created by doing this is induced into the secondary side of the coil where the windings are many turns of fine wire. The result here is an increase in voltage because the number of windings is higher, but it is a lower current flow (high voltage, low current) Try to think of it as a doorbell transformer in reverse. Now, to get all that energy to the sparkplugs:

The high voltage from the coil secondary is taken off the output lug. This is done though the coil wire that goes to the center of the distributor cap. From there, it connects to the flat springy contact on top of the rotor. The other end of that conductor is the wiper part of the rotor. As the rotor turns inside the distributor, it passes each one of the 4 contacts where the sparkplug wires are connected.
If everything is working and the timing is correct, energy is delivered to each sparkplug during the power stroke of that cylinder.
So the distrubutor has a dual function. It controls the primary current through the points and delivers the energy from the secondary side through the rotor to the sparkplugs.

You will need the core, clips etc. The primary wire connects to the points via the terminal screw.

Fri Jul 30, 2004 11:12 am

that's one for the FAQ's page, well said BD.

Now as a post script.

Battery ignition simply replaces the spinning rotor in the magneto with 6 volts of battery voltage through the primary of the coil. everything else remains essentially the same.

Fri Jul 30, 2004 1:22 pm

Thanks BD, I'll try to digest all of that.

The core, clips & wedges were not listed on that's why I didn't know to order them. Should have checked the parts manual better. Are these parts still available?

Fri Jul 30, 2004 1:52 pm

Well said Bigdog :!:

Some of the mag parts are hard to find. The core, the screws and the clips come to mind. I have an extra core if you need it but I'm still having trouble finding the screws and the clips. I have thought about using coupling nuts to make my own screws but haven't had the time. You can use threaded rod through the cap. The only problem with this fix is that the nuts don't fit it the cap very well. As for the wedges you mention. I don't know what you mean. :?

Fri Jul 30, 2004 2:16 pm

Thanks Donny, I would be glad to take the core off your hands - PM me.

For the screws and clips, I can get creative and rig something.

The wedge is part # 251552R1 - don't know what they are for. ????

Fri Jul 30, 2004 2:26 pm

try [url][/url] Mark's magneto's. i'm certain he has the parts you need.

Fri Jul 30, 2004 3:09 pm

Thanks Artc, I've sent him an email.

Fri Jul 30, 2004 6:17 pm

Ken (48 Cub)
Where do you live in Louisville area? I work downtown, Live in Indiana... Ihave a 49 cub with a mag, if you get stuck maybe you could take a look at mine. Send me a pm