Farmall IH 1947 B or C--loses spark after rebuilidng dist?

Hi Folks---We have a Farmall B or C that the student rebuilt his distributer with new parts and now--we get spark for 6 to 8 revolutions at the points--then we lose spark? Have checked a lot of things with multie meter. Coild has power going in and out 6.2 volts and 6.2 to dist --and 6.2 when points are open. But we lose spark. The coild warms up a little which tells me there must be a ground problem somewhere in the dist. Looking for ideas. Yes--We tried different dcondesnros too--but same result. Is the Coil maybe shutting dowon on me after a few revolutions?--has origiranl coil??

What voltage do you have with the points closed? You should have 6 volts going in and 0 volts coming out.

Put a test lamp on the distributors lil side input terminal or else the coil terminal that wires to the distributor, turn the ignition on and crank the engine over (could remove high voltage coil lead so it dont start) and the lamp should flash ON when points are open but then dead OFF when they are closed.

If the light fails to go off the points arent closing fully,,,,,,,, or the distributor dont have a good ground. If it fails to light up the points arent opening,,,,,,,or theres a short like maybe the distributors lil side stud is shorted to case (broken plastic insulator etc),,,,,,,,or the coils primary winding is bad/open..

On a 6 volt coil the primary between the 2 lil terminals ought to read around 1.25 to 2 ohms.

Id make sure the side input stud isnt shorted,,,,,,the dist has a good ground,,,,,,,the points open n close as they should,,,,,,,,the condensor isnt shorted out. If you remove the condensor n she always fires (even tho a weak spark) try yet another condensor.

Its possible when a partly bad coil or condensor warms up they can fail but it takes more then a few minutes before that normally happens. If theres no shorts n the ground is good and its NOT a condensor problem it could be a bad coil.

To be sure its NOT a cap or rotor problem remove the coil wire where it connects to dist cap (leave coil end intact) and place that wire 1/8 away from tractor iron n crnak ehr over n see if she keeps firing????? If so there but NOT with the wire replaced and youre looking for sparks at plug wires n they stop, suspect a cap or rotor problem.....

If you need my entire Troubleshooting Procedure for non sparking post back

John T

Had one one time that had been (rebuilt?) that was all purtyed up with paint. The fellow could not get the engine to run. He had painted the plate the points mount on. I took it back apart and buffed the paint off the plate and it worked fine. The points did not ground out thru the paint. Was easy to find with an ohm meter.

Check the plastic insulator where the coil wire goes through the distributor wall. I had one shorting out there once.

" Quoting John "
Put a test lamp on the distributors lil side input terminal or else the coil terminal that wires to the distributor, turn the ignition on and crank the engine over (could remove high voltage coil lead so it dont start) and the lamp should flash ON when points are open but then dead OFF when they are closed.

If the light fails to go off the points arent closing fully,,,,,,,, or the distributor dont have a good ground. If it fails to light up the points arent opening,,,,,,,or theres a short like maybe the distributors lil side stud is shorted to case (broken plastic insulator etc),,,,,,,,or the coils primary winding is bad/open..
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John ---
I read this three times and I can't understand your meaning.

IF you take the neg. wire off the [-] side of coil and then use test light between that wire and the terminal with ignition on when points Close would act as a switch turning the light on.

The points may be set too tight and swelling/expanding , and staying closed thus causing the coil to feel extra warm, and shutting down the engine.

The wire isn't removed. The test light is between one stud or the other and ground, with the wire connected. With it disconnected, the points wouldn't even come into play as a switch.

The layman's explanation -- that is the best I could offer -- There is always juice on the ground side of the coil or at the stud on the distributor. When the points are open without a test light, there is no circuit to ground and nothing's happening. When the points are open with a test light, the juice runs through the light to ground, lighting up the bulb. When the points close, they make a ground (very like a dead short but not exactly). Without a test light, they complete the circuit that lets the coil build a charge. When a test light is connected, they do the same thing because the current will take the path of least resistance (direct ground vs. the resistance of a bulb filament on the way to a ground), and flow through the points rather than through the bulb in the test light.

Yes Scotty I understand , but if you take the wire off and then touch it with the test probe, with other end to [-] side of coil, if there is a short in the distributor with ign. on it will show up immediately, or if points operating properly should flash test light on and off when making contact during the rotation of the rotor.

it's just that it needs two people to do it this way.