HOT COIL

Bonnie Tallman · Aug 20, 2009

I am trying to get an old farmall M running. There are problems with the ignition and/or the starter switches - so for now I am by-passing those switches and hot wiring from the pos battery cable to the starter to just get the tractor to start.

However - I have had two coils get so hot they cracked and oil leaked out. What would cause this to happen? I am using a 12 V battery and a 12 volt coil. I have the ignition wire running from the pos battery terminal to the pos coil terminal - the condenser is connected to this same pos coil terminal. A short 14 gauge copper wire is connected from the negative coil terminal to the distributor. I have new plugs and plug wires. The tractor will start and run for maybe 5 -10 seconds and then stops - acts like it is not getting enough gas - however after about three attempts at starting the coil then gets extremely hot. Any ideas? Thanks

Bob Kerr · Aug 20, 2009

If you are wiring it up with straight 12v then you may need a ballast resistor in line with the 12v input to the coil. Also if you leave the coil hooked up while tinkering and the points are closed, it will get hot for sure. One more question, was the tractor converted to 12 or did you just put a 12v batt and coil in and call it good?

John T · Aug 20, 2009

On that 12 volt tractor you claim youre using a 12 volt coil, and thats all fine n dandy IFFFFFFFFFFFF its really a full true 12 volt coil.

I say that because if a coil is labeled: "12 volts for use with (or requires) external ballast resistor" its in reality a 6 volt coil and indeed requires the external ballast (just like it says DUH) otherwise it overheats badly.

A full true 12 volt (some call internally ballasted) coil may be labeled "12 volts" or "12 volts NOT for use with ballast resistor" and thats the kind you need on a 12 volt system with no external ballast. Its internal primary winding resistance between its lil + and - terminals will be in the 2.5 to 3.5 or so ohms range if its a full true 12 volt coil no ballast required.

Theres a condensor inside the distributor thats in paralell with the points, Im not sure whats going on with one at the coil unless its there to reduce radio interference.

Even the right coil (or coil + ballast) gets fairly hot if the ignition is left on a good while n shes NOT running.

John T

ScottyHOMeY · Aug 20, 2009

You need to check out Bob's idea about the resistor and whether or not your coil needs one.

More to the point, if your condenser is hooked up as you say, it's wrong. If you are set up for negative ground (battery - to chassis) the + terminal on your coil should be connected only to the hot lead from the battery/switch. The wire connected to the - terminal on the coil should run down to the distributor body and connect to an insulated stud on the outside of the distributor body that conducts the juice to the points and condenser, which are connected together inside the body to the inside of the stud.

You've either got the condenser in the wrong place, or what you're looking at is not a condenser.

Bonnie Tallman · Aug 20, 2009

Hum - the condenser was connected to the + terminal on the coil - and has been for years...so I figured it belonged there. THere is a condenser in the distributor also. (I bet you knew that). The 12 volt coil says internal resister on the outside. Perhaps I allow too much time to elapse between attempts to keep it running. Switiching topics - what would cause it to start quickly - run nice and smooth for a few seconds - -then stop? I will remove that condenser from the + coil terminal.

Nick Lenarz · Aug 20, 2009

Ditto on the ballast resistor. I got mine from an auto parts store, ask for a "Ford ballast resistor" and most places will know what you mean. They"re 5-ohm, 50 watt ceramic resistors, and are made to mount right to that little "ear" on the coil strap. I had similar trouble with my M"s coil overheating, and after I installed the resistor, no more problems.

6-volt and 9-volt coils were in use in cars even up to the mid 80s- both our "82 Jeeps had them, and used dozens of feet of resistor wire instead of ballast resistors.

If you want to do away with the resistor issue altogether, look into converting to an "e-frame" coil such as out of a 90"s Ford or Jeep. They"re true 12v, smaller than a can-style coil, and give a hotter spark for better combustion. Takes away coolness points as it"s obviously not factory original, though.

JMOR · Aug 20, 2009

(quoted from post at 22:25:23 08/20/09) Ditto on the ballast resistor. I got mine from an auto parts store, ask for a "Ford ballast resistor" and most places will know what you mean. They"re 5-ohm, 50 watt ceramic resistors, and are made to mount right to that little "ear" on the coil strap. I had similar trouble with my M"s coil overheating, and after I installed the resistor, no more problems.

6-volt and 9-volt coils were in use in cars even up to the mid 80s- both our "82 Jeeps had them, and used dozens of feet of resistor wire instead of ballast resistors.

If you want to do away with the resistor issue altogether, look into converting to an "e-frame" coil such as out of a 90"s Ford or Jeep. They"re true 12v, smaller than a can-style coil, and give a hotter spark for better combustion. Takes away coolness points as it"s obviously not factory original, though.

Sorry, Nick, but 5 ohm ballast is out of the question for anything...can't possibly be what you mean.

Brownie 450 · Aug 21, 2009

Wondering if the condenser in the distributor is getting weak [shorting] after a short time of running. You could try a new condenser & see what happens.

SDE · Aug 21, 2009

Starting and running good and then running rough could be a fuel restriction.

Janicholson · Aug 21, 2009

I believe the condenser on the coil will do no harm (it may have been put there to reduce radio noise), but it is effectively not an issue.
The ignition must be shut off between attempts to start it. The fuel system needs to be checked for supply to the carb, and then float level etc. The correct coil will have 12v no external resistor required. Or it will say external resistor required. If it needs one, use a chrysler or GM resistor, ford primarily used resistor wire in the loom. JimN

300farmall · Aug 21, 2009

You need a resistor have had this problem and it was the fix.

Bonnie Tallman · Aug 23, 2009

Thanks - Can you give me some hints on what would cause fuel restriction, other than the obvious - -no gas in the tank, or a plugged fuel line from the tank to the carburator.

HOT COIL

Bonnie Tallman

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Bob Kerr

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John T

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ScottyHOMeY

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Bonnie Tallman

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Nick Lenarz

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JMOR

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Brownie 450

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300farmall

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