No spark

[huntsabunch]

Looking for some help on a 1968 Farmall 140. I have tried everything and can't get a spark from my ignition. It's a 12 volt, generator style with a starter button (no solenoid). It has new points, condenser, rotor, coil and the plugs/wires are almost new. Points were set to .020 and i have power to the high voltage side of the coil which is internally rectified. Not sure which side of the coil should be connected to the distributor since i've seen 12 volt diagrams showing both pos and neg. I have traced all wires from regulator, generator, voltmeter, etc. for proper location and checked each for breaks with a continuity tester. Still can't get a spark out of the distributor. Could someone please guide me through the steps to locating the problem? I also checked the specs on the coil, even though it was new. It reads 3 on the high side and 10 on the low.

 

[staninlowerAL]

1.Test the coil output by connecting a 12v power directly to the + side of the coil and insure that the power is passing through the coil from the - side of the coil to ground. Pass or Fail test
2. Connect the coil - to the input side of the distributor and with the engine turning the points should arc as they open and close. Pass or fail test.
3. After the points are breaking the path to ground as they arc check the high voltage output (tower) of the coil to ground. It should be about 18-20k volts. Pass or fail test.
4 Test the spark from the tower to the center of the dist. cap, if good then on to plugs. Pass or fail test.
5. When you have spark at the plugs if the engine does not try to start check the timing.
This is assuming that the system is neg ground. JMHO Stan

 

[DJ54]

If your battery is set up for a negative ground, hot wire from switch should go to the + side of coil, wire to distributor to the - side of coil.

Check to make sure your points didn't slip, and set them to the .020 on a high lobe in the distributor.

You can check voltage out of the coil with a simple test light, turning the engine over with the starter with the switch on. Test light should flash when turning the engine over. Also check for voltage inside the distributor on the stud coming through the side. Those Bakelite insulators have been known to crack and cause a short. There are replacements. IF you have voltage to the inside, with points closed you should be able to manually break/spread the points, and you should see a spark.

Are you not getting spark, or is it just not firing..?? With new plug wires, were they replaced in correct rotation..??

 

[Gary Dotson]

First, where did your ignition parts come from, there are lots of cheap poor quality ones out there. Next, did you burnish the contact surfaces of the points, they often have a protective coating on them, polish with a piece of brown paper. Look at you new points and compare them to the original, we’ve encountered several with the plastic rub block attached backward. A simple test light will go a long way to diagnosing the problem, no meter needed. Also, in recent times there have been a number of shorted condensers turn up. That kills the spark dead. Follow DJ tests above, you should find the problem in pretty short order.

 

[huntsabunch]

1.Test the coil output by connecting a 12v power directly to the + side of the coil and insure that the power is passing through the coil from the - side of the coil to ground. Pass or Fail test
2. Connect the coil - to the input side of the distributor and with the engine turning the points should arc as they open and close. Pass or fail test.
3. After the points are breaking the path to ground as they arc check the high voltage output (tower) of the coil to ground. It should be about 18-20k volts. Pass or fail test.
4 Test the spark from the tower to the center of the dist. cap, if good then on to plugs. Pass or fail test.
5. When you have spark at the plugs if the engine does not try to start check the timing.
This is assuming that the system is neg ground. JMHO Stan

Thanks so much for the info. I got as far as testing for voltage out of the tower. my meter doesn't go that high and won't read anything if voltage is exceeded. I have a spark at the points. Rain here today so I'll see what i can do tomorrow. Stay tuned and thanks again.

 

[huntsabunch]

1.Test the coil output by connecting a 12v power directly to the + side of the coil and insure that the power is passing through the coil from the - side of the coil to ground. Pass or Fail test
2. Connect the coil - to the input side of the distributor and with the engine turning the points should arc as they open and close. Pass or fail test.
3. After the points are breaking the path to ground as they arc check the high voltage output (tower) of the coil to ground. It should be about 18-20k volts. Pass or fail test.
4 Test the spark from the tower to the center of the dist. cap, if good then on to plugs. Pass or fail test.
5. When you have spark at the plugs if the engine does not try to start check the timing.
This is assuming that the system is neg ground. JMHO Stan

If your battery is set up for a negative ground, hot wire from switch should go to the + side of coil, wire to distributor to the - side of coil.

Check to make sure your points didn't slip, and set them to the .020 on a high lobe in the distributor.

You can check voltage out of the coil with a simple test light, turning the engine over with the starter with the switch on. Test light should flash when turning the engine over. Also check for voltage inside the distributor on the stud coming through the side. Those Bakelite insulators have been known to crack and cause a short. There are replacements. IF you have voltage to the inside, with points closed you should be able to manually break/spread the points, and you should see a spark.

Are you not getting spark, or is it just not firing..?? With new plug wires, were they replaced in correct rotation..??

I could not get a spark at the plug using the usual method of taking it out and grounding against the block. The tractor had been sitting for some time (couple years) so I went ahead and replaced the ignition parts hoping that would do it. It didn't, so i went looking for a wiring diagram, That's when it got confusing. There's a bit of contradiction out there, not to mention the 6 volt positive ground, 12 volt negative ground stuff. I know you guys will get me straightened out sooner or later. I got my parts from Steiner so I don't think they are the problem. Thank you for your response.

 

[staninlowerAL]

I could not get a spark at the plug using the usual method of taking it out and grounding against the block. The tractor had been sitting for some time (couple years) so I went ahead and replaced the ignition parts hoping that would do it. It didn't, so i went looking for a wiring diagram, That's when it got confusing. There's a bit of contradiction out there, not to mention the 6 volt positive ground, 12 volt negative ground stuff. I know you guys will get me straightened out sooner or later. I got my parts from Steiner so I don't think they are the problem. Thank you for your response.

You can check for spark from the coil tower (high voltage) by removing the wire from the dist cap and see if it will arc to ground as you try to crank the engine. If this works, and you can't get a spark from the plug wire to ground then suspect a problem with the dist cap or rotor. 6v. 12v. pos or neg ground does not matter. Also you could substitute a known good coil for a test and see if it makes any difference. Sometimes new. out of the box parts are faulty. Take a look at Board Shortener Tom's post from the Farmall Cub Forum about new parts: https://farmallcub.com/community/threads/buyer-beware.118255/ Sad to say but it's true. I had one about 2 years ago that would arc at the points on every revolution of the engine but would not arc to ground from the coil tower. Turned out to be a faulty coil. I substituted a known good coil and it started immediately. Stan