Stumped - no spark

[DD in WA]

The back story is I've a '42 H, 12 volt I got from my late uncle. It was running fine, then not so good, then dead. Determined it had no spark and upon further investigation noticed the distributor wasn't rotating. I pulled it and not having been greased in who knows how long it stripped teeth off the dist. and bent the shaft. So I bought another from JP Salvage in MO. Cleaned it up, added new points, condenser and rotor (cap was new) and put it on. No spark. Tested the coil with a multimeter and the + to - was 3 ohms and + to center was 9 something, both within spec. I then checked voltage with the ignition on to the + on the coil and it was 12.3 and the - was the same (this with the points closed). I cranked the engine by hand to where the points were open and checked the voltage at the - terminal (small wire going to the distributor) and it was still 12.3 volts. If I understand correctly with the points open it should be 0. So I figured the coil was bad. Bought a new one and installed it and still nothing (tested and same 12.3 volts on the - terminal with the points open). I had checked earlier if the post in the distributor was touching the side of it and it wasn't. So where do I go from here??? Is there a short somewhere perhaps or have I reinstalled something wrong?? Appreciate your thoughts.

 

[300guy]

When the points are closed you should have 0 on the negative side. You have a open circuit someplace from the coil to the points. When the circuit is open like when the points open, the meter completes the circuit thus the 121.3 volt reading.

 

[Janicholson]

The back story is I've a '42 H, 12 volt I got from my late uncle. It was running fine, then not so good, then dead. Determined it had no spark and upon further investigation noticed the distributor wasn't rotating. I pulled it and not having been greased in who knows how long it stripped teeth off the dist. and bent the shaft. So I bought another from JP Salvage in MO. Cleaned it up, added new points, condenser and rotor (cap was new) and put it on. No spark. Tested the coil with a multimeter and the + to - was 3 ohms and + to center was 9 something, both within spec. I then checked voltage with the ignition on to the + on the coil and it was 12.3 and the - was the same (this with the points closed). I cranked the engine by hand to where the points were open and checked the voltage at the - terminal (small wire going to the distributor) and it was still 12.3 volts. If I understand correctly with the points open it should be 0. So I figured the coil was bad. Bought a new one and installed it and still nothing (tested and same 12.3 volts on the - terminal with the points open). I had checked earlier if the post in the distributor was touching the side of it and it wasn't. So where do I go from here??? Is there a short somewhere perhaps or have I reinstalled something wrong?? Appreciate your thoughts.

300 guy has it. The points make a complete circuit to ground when closed. This turns on the coil and in milliseconds builds a magnetic field in the coil. when the points open, this field collapses and the collapsing field creates the high voltage in the plug wires. The condenser absorbs some of the energy that would burn the points, and helps make the spark jump the plug gap more than once. Look up Kettering ignition if you want more.
One more issue is that new points are often coated with corrosion inhibitor and need cleaned with lacquer thinner, or fingernail polish remover and a q-tip slightly dampened in it, to remove the insulating goo. Jim

 

[used red MN]

When the points are working properly your meter should continually bounce back and forth between reading 12 volts and zero to ground while cranking the engine. Actually a test light is best to use, it will flash on and off as the points open and close.

 

[Brownie450]

Is there a resistor in the circuit leading from the ign.
switch to the dist? This Voltage dropping resistor
could be a problem not giving full voltage to the
dist. while still letting your meter show 12 Volts at
the dist./ coil terminals.
Jim

 

[DD in WA]

300 guy has it. The points make a complete circuit to ground when closed. This turns on the coil and in milliseconds builds a magnetic field in the coil. when the points open, this field collapses and the collapsing field creates the high voltage in the plug wires. The condenser absorbs some of the energy that would burn the points, and helps make the spark jump the plug gap more than once. Look up Kettering ignition if you want more.
One more issue is that new points are often coated with corrosion inhibitor and need cleaned with lacquer thinner, or fingernail polish remover and a q-tip slightly dampened in it, to remove the insulating goo. Jim

Good info. I looked up Kettering like you suggested which was helpful. I'll clean off the points as you suggest. Could my problem perhaps be that I'm not getting a good ground through the distributor body itself? I did paint the "new" dist. before installing it...

 

[DD in WA]

Is there a resistor in the circuit leading from the ign.
switch to the dist? This Voltage dropping resistor
could be a problem not giving full voltage to the
dist. while still letting your meter show 12 Volts at
the dist./ coil terminals.
Jim

No resistor.

 

[used red MN]

Good info. I looked up Kettering like you suggested which was helpful. I'll clean off the points as you suggest. Could my problem perhaps be that I'm not getting a good ground through the distributor body itself? I did paint the "new" dist. before installing it...

Yes, the paint could be your problem but it is fairly rare to encounter this. After cleaning the points as Jim suggested if you still read voltage on the distributor lead with the points closed do this test. Ground your negative meter lead to a good chassis ground maybe even back to the negative battery post, when the points are closed the base of the distributor should show no voltage difference between it and the chassis. If it does show voltage clean the paint off under one of the distributor hold down clamps this should eliminate that problem. Make sure by repeating the test. I am assuming that it has been set up negative ground when converted to 12 volts. In you explanation above about the coil you mention (+) and (-) are you referring to the actual markings on the coil? If so it sounds correct, originally your tractor would have been positive ground. For a 12 volt conversion the negative ground is good. If you install an alternator it will need to be negative ground.

 

[300guy]

When the points are closed you should have 0 on the negative side. You have a open circuit someplace from the coil to the points. When the circuit is open like when the points open, the meter completes the circuit thus the 121.3 volt reading.

OPPS that should have been 12.3 volts not 121.3.

 

[DD in WA]

Yes, the paint could be your problem but it is fairly rare to encounter this. After cleaning the points as Jim suggested if you still read voltage on the distributor lead with the points closed do this test. Ground your negative meter lead to a good chassis ground maybe even back to the negative battery post, when the points are closed the base of the distributor should show no voltage difference between it and the chassis. If it does show voltage clean the paint off under one of the distributor hold down clamps this should eliminate that problem. Make sure by repeating the test. I am assuming that it has been set up negative ground when converted to 12 volts. In you explanation above about the coil you mention (+) and (-) are you referring to the actual markings on the coil? If so it sounds correct, originally your tractor would have been positive ground. For a 12 volt conversion the negative ground is good. If you install an alternator it will need to be negative ground.

Will do. Yes, it is now negative ground and the +/- are the actual markings on the coil.

 

[DD in WA]

Yes, the paint could be your problem but it is fairly rare to encounter this. After cleaning the points as Jim suggested if you still read voltage on the distributor lead with the points closed do this test. Ground your negative meter lead to a good chassis ground maybe even back to the negative battery post, when the points are closed the base of the distributor should show no voltage difference between it and the chassis. If it does show voltage clean the paint off under one of the distributor hold down clamps this should eliminate that problem. Make sure by repeating the test. I am assuming that it has been set up negative ground when converted to 12 volts. In you explanation above about the coil you mention (+) and (-) are you referring to the actual markings on the coil? If so it sounds correct, originally your tractor would have been positive ground. For a 12 volt conversion the negative ground is good. If you install an alternator it will need to be negative ground.

Cleaned off the points and with the points closed I'm getting about 60 mV on the neg coil terminal. Closer but not zero. At least this is progress. I'll keep at it and see if I can get it to zero, it's just too darn cold in the barn to work out there for any length of time.

 

[used red MN]

Cleaned off the points and with the points closed I'm getting about 60 mV on the neg coil terminal. Closer but not zero. At least this is progress. I'll keep at it and see if I can get it to zero, it's just too darn cold in the barn to work out there for any length of time.

Holy moly, 60mv is close enough! Do you have a 12 volt test light? If it will not light that, which I am sure it won’t you are good to go! Zero in this context is a relative term.

 

[DD in WA]

Holy moly, 60mv is close enough! Do you have a 12 volt test light? If it will not light that, which I am sure it won’t you are good to go! Zero in this context is a relative term.

Correct, the test light didn't light. Opened the points and it does. Tested for spark and it's there!!! Thanks a million!