Ignition Coil

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wfmdfm
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Ignition Coil

Postby wfmdfm » Sun May 31, 2015 8:57 am

After trouble shooting I determine that my coil was not producing a spark. After removing the coil and getting ready to head out I had it in my hand and realized it was full of water. Looks like my trouble shooting was correct. After replacing the coil with a Tractor Supply coil it still would not start. Points were cleaned and reset but still not spark. Now I have run down my 6 volt battery. I jump it with a 12volt and it starts right up. Charge up the 6 volt and give it a try the next day and same thing wont start but it cranks fine. Try the 12 volts and it starts right up. So my question now is 6 volt coil vs 12 volt coil. The one I purchased claims to be 6 volt with or without external resistor. Where would this resistor be on the tractor if I had one?
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Re: Ignition Coil

Postby drice » Sun May 31, 2015 9:23 am

u can add one to it its not that hard. but I would make sure I had a six volt coil first the coil just heats up with out it.

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Re: Ignition Coil

Postby Eugene » Sun May 31, 2015 10:20 am

Resistors are used on 12 volt systems to drop the voltage to the points to 6 volts. 6 volt generator system- no need for a resistor.

The resistor on a 12 volt system commonly uses a Chrysler ballast resistor. The resistor is commonly located in the vicinity of the coil. Google Chrysler ballast resistor. Up will pop photos of several configurations of the resistor.
I have an excuse. CRS.

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Re: Ignition Coil

Postby Eugene » Sun May 31, 2015 3:45 pm

Multimeter, 20 volt DC setting. One lead to terminal on side of distributor or terminal on top of coil leading to distributor. Other lead to ground.

Tractor out of gear. 6 volt battery. Ignition on. Roll engine by hand - rotate fan until you get a voltage reading. You should get battery voltage at either terminal, 6 volts.

Take your 6 volt battery to the auto parts store and have it tested. Battery could show 6 volts when tested with a multimeter, but not have sufficient amps to crank over the tractor.
I have an excuse. CRS.

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bob in CT
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Re: Ignition Coil

Postby bob in CT » Sun May 31, 2015 5:30 pm

Eugene wrote:Multimeter, 20 volt DC setting. One lead to terminal on side of distributor or terminal on top of coil leading to distributor. Other lead to ground.

Tractor out of gear. 6 volt battery. Ignition on. Roll engine by hand - rotate fan until you get a voltage reading. You should get battery voltage at either terminal, 6 volts.

Take your 6 volt battery to the auto parts store and have it tested. Battery could show 6 volts when tested with a multimeter, but not have sufficient amps to crank over the tractor.


He said a charged battery cranks over the engine. Sure seems like it is the coil.

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Re: Ignition Coil

Postby Larry B » Sun May 31, 2015 10:16 pm

You should be using a 1.5 ohm coil, commonly called a 6 volt coil and not a 3 ohm coil commonly called a 12 volt coil and you do NOT need a ballast resistor. If you have a multimeter disconnect the wires from the 2 screw terminals and measure the the resistance. Should be approx 1.5 ohms. If it is approx 3 ohms you have a coil for a 12 volt system.

You can easily test the ignition system with no special tools.
1. remove the distributor cap and turn crankshaft till the points are closed (I turn the engine with the front pulley).
2. Connect one end of a spark plug wire from the coil tower and place a 1/4 x 20 bolt in the other end.
3. Turn on the ignition switch and hold the end of the spark plug wire about 1/4" from ground and use something non-conductive to open the points. If you get a blue white spark that will jump a 1/4" air gap it will run your cub. If you don't get a good spark could be a low battery, pitted points. wrong coil, poor electrical connection, etc.

Never let an engine with a point ignition set for a long time with the key on and the engine not runing. If the points are open there is no problem but if the points are closed the coil has a constant 4 amps of current flowing in it and can shorten the coils life from overheating. I have found the Pertronics coils much more durable than the onse from Tractor supply. It is also not very healthy for the point spring either.


Larry B

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Re: Ignition Coil

Postby bythepond88 » Mon Jun 01, 2015 4:37 pm

Does it keep running after you remove the jumper cables? It could be a bad ignition switch. I had that problem, the switch wasn't passing enough voltage to the coil. With 12 volts, the switch could be passing enough voltage to fire the plugs.
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Re: Ignition Coil

Postby Larry B » Tue Jun 02, 2015 5:01 pm

Knda sounds like he may have a 3 ohm (12 volt) coil on a 6 volt system. If the voltage drops to about 5 volts during cranking and he has a 3 ohm coil he will have 5 (volts) / 3 (ohms) = 1.67 (amps) then 1.67 (amps) X 5 (volts) = a whoping 8.3 (watts) of power at the coil. Not enought to make it fire the plugs. But if he uses 12 volts to start the tractor and the charging system is charging at 7 volts then 7 (volts) / 3 (ohms) = 2.3 (amps) then 2.3 (amps) X 7 (volts) = 16.1 (watts) which will probably be enough to fire the plugs. A 6 volt tractor charging at about 7 volts with a 1.5 ohm coil runs at about 32 watts normally. A multi meter could probably solve the mystery.

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wfmdfm
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Tractors Owned: .
1947 Circle Cub #1110
1947 Circle Cub #1316
1948 Cub #43915
1966 Power King
189 two way Plow
54A Blade
144 Cultivator
26 ft Welcraft
1967 Case 530ck Backhoe
Location: Middleboro Massachusetts

Re: Ignition Coil

Postby wfmdfm » Wed Jun 03, 2015 1:25 pm

Well issue is solved. Picked up a coil at NAPA and installed it. It fired right up. The Tractor Supply coil is clearly marked 6 volts and measures 1.9 ohms. With all my troubleshooting (1.9 ohms thru me off) I figured it must be a issue with the coil. Thanks for all the feed back. I am not sure its solved but its fixed.
Wally
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