1947 Farmall B no spark

Tractor is on 12v. After getting it running and letting her warm up a good 20 minutes. I shut it down. It ran great. After dinner I go to pull it out of the shop and put it away and I am back to no spark. It has new points, plugs, condenser. I have good voltage on both sides of the coil with the side distributor wire disconnected. Snapping the points open does not cause the coil to fire with center lead near ground. I am thinking maybe "old" was right about the insulated stud on the side of the distributor being bad. Anything else I should check? I am chasing phantoms and that tends to end up being weak insulation someplace that shorts randomly. Any thoughts?

Seems like yours or a similar question was posted a few days back??????

IFFFFFFFFFF the distributors insulated pass through stu/terminal is indeed shorted out as you mentioned, she will never fire and a test lamp on the coils output (to distributor) terminal when wired up to distributor WILL NEVER LIGHT UP SEE BELOW!!!!!!!!!!!!!!!!!


Here are the tips I posted then, which of course, includes info about the distributors insulated side pass through insulated bushing possibly being shorted as a possible (along with several other) cause.

1) With the ignition on there should ALWAYS be voltage (with respect to frame ground) on the hot INPUT (NOT to distributor) side of the coil.....

2) Over on the coils other OUTPUT terminal:

Hot battery voltage when points are open
ZERO volts when points are closed

Therefore, if the engine is cranked over slowly a test lamp on the coils output (to distributor) should flash ON (points open) and OFF (points closed)

If the lamp never goes off (should when points are closed) the points arent fully closing or,,,,,,,,,,,,,, are burned/carboned severely and not conducting or,,,,,,,,,, the points or distributor isnt well grounded

If the lamp never comes on (and all else is okay), condensor is shorted,,,,,,, or points are shorted out or remain closed,,,,,,, or points or condensor wires are shorted or,,,,,,,,,,, the distributors insulated side pass through stud/terminal is shorted or else the coils LV primary is bad/open

Work through this for more tips and diagnosis


http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition Troubleshooting

As I said the other day move the crank so the points are open. Take one of the 2 small wires off the coil does not matter which one be it distributor side or ignition side and if you get a spark when you hook and unhook that wire you have a short in the distributor be it the insulator or you have one of the wires from the condenser etc shorting out. No test light needed but you do need to be where the sun light is not so bright as to hide the small spark that you should not see

Thanks Rich, I think I was pretty clear that I have it narrowed down to a short in the distributor. I don't really see a lot of places other than the stud for there to be a short. The points/condensor are new. I'll have to have a look around in there and see if there is something making contact that should not be. I suppose that jumper from the coil to points could be shorting to the distributor housing too. That would be a good source since it it is an on again off again problem I am thinking the wire could be a likely culprit. Appreciate your thoughts.

sometimes the spring on the points will touch a screw head or something. that will kill your spark.

If you have that spark as I said when you unhook and hook the wire to the coil then remove the wire from the points and make sure it is not touching any thing. If you still get that spark then it is a bad insulator going in the side of the distributor. If that is so what I do is remove the insulator then run a wire in the side of the distributor and seal that wire off with silicone then it is a fixed problem unless your wanting it to look like it was new. I have a ford 841 that has been set up that way for well over 25 years now

The short you suspect ought to be easy to find.

An ohm mter or simple continuity tester on the side terminal with other lead to case ground ought to register:

CLOSED CIRCUIT SHORT (Low resistance) WHEN POINTS ARE CLOSED

AN OPEN CIRCUIT (High approaching infinity resistance) WHEN POINTS ARE OPEN

If its ALWAYS is a short to case ground, the problems either:

Points are staying closed,,,,,,,,,,Condensor is bad and shorted out (Ive seen new ones out of the box bad and shorted out, try unhooking it n see if that fixes the short) ,,,,,,,,,,,Wires to condensor or points are shorted out to case ground,,,,,,,,,,,,,Points have a short (I have seen the springs shorted),,,,,,,,,,,,Side pass through insulated bushing terminal (where coil wire attaches) is shorted out.

Once more,,,,,,,,,,, a simple cheap DC test lamp placed on the distributors terminal or on the coils output with ignition on and if all else is wired correct and working SHOULD LIGHT UP WHEN POINTS ARE OPEN AND GO OFF WHEN THEY ARE CLOSED and if not re read my post below to see why and the possible problems

HOPE THIS HELPS, LET US KNOW WHAT YOU FIND

God Bless n best wishes

John T
John Ts Ignition troubleshooting

Sure enough, Ive seen that happen

John T

I have seen new points shorted on the pivot pin so be sure to look at everything, stumper

And mayhap you have again. I was out there looking at all the possibilities inside the distributor and, just because he mentioned it, I gave the spring for the points a once over and it looked like it may be too close to the back of the distributor. I pried it forward a bit and reassembled and it fired up...reluctantly because the plugs were fouled again. Just went out this evening and it started right up and backed into the shop for the night. Now it stopped dead while I was closing the overhead door leading me to believe that I will be looking at it again on Friday. But for tonight I decided not to go looking for trouble.

I have all your posts and notes copied into my archives for future reference. Many thanks to all for the help!