Coil Resister

[BeaverIslander]

Today my 49' 8N did not want to start. When I initially turned the key it didn't feel just right so I thought maybe it was not turned all the way off and possibly burnt the points, but that was just guessing on my part. My neighbor worked on these as a kid and soon determined that the coil was the issue. There is a copper or brass spring that had gotten hot and almost burnt through, and in fact part of it broke off as we were looking at it. The previous owner had converted it to a 12V system. So do I get a 12 volt or the 6V coil? He also thought that there should be a 12v to 6v resister in it, which it doesn't have. Could someone please tell me what I need to get me back up and running?
Thanks.

 

[Bruce (VA)]

First, check out tip # 38. Leaving the key on caused the problem.

Then, to answer your question, see tip # 30.

Get a 12v coil & use ONLY the OEM ballast resistor, as in the picture.

Technology & materials being what they were in the 30's, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm's Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance.

75 Tips

 

[Royse]

Bruce gave you the right answers here.
I would add if the switch didn't "feel" right, test it and/or change it.
No sense putting a new coil and points in it if they're just going to burn up again.
Switch is about $9. Cheaper than the points or coil.

 

[BeaverIslander]

I think this guy put some aftermarket key switch
on it. There are 3 wires, if you turn the key to
the left, just the ignition is on, in the middle
is off, and to the right the ignition and lights
are on. It looks like the one on this site has 2
wires...is that what I need?
Also, could someone double check me to be sure
these are the correct parts numbers that Bruce
referred to?

12 Volt Coil - 12VOLTCOIL (replaces 9N12024-12V)
Resistor Assembly A8NN12250A
Distributor Gasket Kit 9N12104
Key Switch 8N3679C

 

[Royse]

Yes, those part numbers look right to me.
The two wire switch was only to run the ignition.
The lights would be wired so that they can be used any time.
Hot wire to the common voltage post on the resistor.
Many of us would like to have them turn off with the key, but
the key switch cannot handle the current required for the lights
and burns up faster if wired that way.

 

[Hobo,NC]

Resistor Assembly A8NN12250A

There are two of'em A8NN12250 A&B the difference is the size of screw used to mount them the resistor is the same... A should get'er done fer ya...

Distributor Gasket Kit 9N12104

Only one kit that I know of

Key Switch 8N3679C

The reproduction switch is a P.O.S. good luck... If you are gonna run one replace the amp meter with a voltmeter then you will know when the switch fails... I would put a voltmeter on it anyways cuzz a amp meter is a useless P.O.S. also...

Amp-meter lubbers have a hard time making the switch that's why you will see no crank and no start post go on for weeks and take up pages here...

 

[BeaverIslander]

Thanks for the help, order has been placed.

 

[souNdguy]

Now hobo.. look at what you wrote.

If the poster takes your advice verbatum and'replaces his ammeter with a voltmeter' do you think his tractor will start?

it's not a direct drop in replacement!

 

[BeaverIslander]

A quick thank you to the folks that helped me with this latest project. I put in the new points, coil and resistor today and it came roaring back to life. Have a new ignition switch ready to go, maybe tomorrow.

 

[Bruce (VA)]

You're welcome. Glad to help.

And thanks for the follow-up; we all like to hear success stories!
75 Tips