Farmall Cub

I have a 1950 cub, 6 volt system, battery ignition. Yesterday, I was pulling a wagon with this tractor and had been doing so for about 30 minutes with no problems whatsoever. With no warning, while parked and idling, the tractor stalled. It would not re-start. It just turned over and over with no sign of firing. It had plenty of gas in the tank.

I have not had time to do much investigating, but I did notice one interesting thing: Normally, when I pull the ignition switch out before starting the tractor, the ammeter shows a slight deflection towards the "discharge" side. If I push the switch back in, the ammeter returns to zero. But after the tractor stalled yesterday, the ammeter did not respond at all to the switch. Pushing the switch in or pulling it out had no effect on the ammeter. I know the ammeter is working, because I turned the headlights on and saw a large deflection (approx. 15 amps) towards "discharge". I tried starting the tractor several times, and each time I watched what happened to the ammeter while it was turning over. The ammeter actually showed a very slight deflection towards the "charge" side while the engine was turning over (maybe 2 amps). Normally, the ammeter would show a large discharge while the engine is turning over.

Would I be correct in assuming the switch has gone bad? Is there some easy way to find out if it is bad? The funny thing is, I replaced this switch about 2 years ago, so I would be surprised if it went bad this soon. Maybe I just got a bad switch.

Any help you can give me would be much appreciated, as I am no electrical expert. Thanks.

Probably ingition coil or distributor condenser failure. Ed

Very simple to trouble shoot your ignition switch on a coil sparked tractor.

Obtain a jumper wire of the appropriate length to reach the coil from the battery.

Attach one end of the wire to the power terminal of the battery, (the ungrounded terminal) the other to the coil. The coil has 2 primary wire posts, connect to the post OPPOSITE of the post connected to the distributor.

If it starts and runs, start isolating sections of the system. For instance, with a test light or multi meter, look for power feeding the switch. If the switch has power, test the opposite side of the switch for power when it is switched on. If that checks out, suspect the wire running from the switch to the terminal of the coil you had your hot wire on.

From the factory, this wire runs in a bundle through the hood clips towards the front to the coil. I have recently experience the rockshaft on my 51 rubbing through the bundle of wires shorting the wire running to the coil stopping the tractor dead in its tracks.

Remember with the tractor hot wired the switch will no longer turn it off. You must remove the jumper wire.

Good luck with your search.

I neglected to address your ammeter question.

Current drawn directly from the battery by the starter is not registered on the ammeter. The only amperage draw reflected on the meter is what is drawn through the main feed wire connected to the battery by way of the starter which would include the ignition system and all the lighting accessories connected to the light switch.

If you have any accessories connected directly to the battery, their current draw would not be registered either.

Additionally, if the engine stops with the points open, there may be little or no current draw reflected on the ammeter when the ignition switch is operated as the coil only charges up for the spark when the points are closed.

EDITED 10/17/2012, 19:37 Missing words: when the ignition switch is operated

I'd pull the center coil wire off the distributor cap and hold it 1/4" from the frame while cranking the engine with the ignition switch on. If you don't see a blue spark and hear a "tick tick tick" noise, you lost spark for some reason.

What you're seeing on the ammeter is normal. Lights will discharge. Generator spinning (even with the starter only) will charge.

lazyuniondriver wrote:Obtain a jumper wire of the appropriate length to reach the coil from the battery.

Actually, you can run the jumper from the post where the battery cable connects to the starter up to the coil. Much shorter. That's currently the way mine is hooked up (bad ignition switch, and I haven't had the time to pull the dash to replace it yet). I have a male/female quick disconnect in the middle of the jumper, to make switching on and off easier (put the male on the end going to the coil to eliminate the possibility of sparking when disconnected).

bythepond88 wrote: Actually, you can run the jumper from the post where the battery cable connects to the starter up to the coil. Much shorter.

That is a true statement however I highly discourage people from starting equipment from standing on the ground. There are way too many safety issues invoved from cranking or starting motor equipment from anyplace other than the operators seat.

You have your male/female disconnect system which works for you. I would have a lanyard on it to break the circuit from the operators platform if an emergency arose, myself never being able to lean forward enough to unclip a wire at the starter.

I try to never give dangerous trouble shooting advice (not that yours was dangerous by any stretch of the imagination) however I figure you have a better chance of pulling the wire off the battery than the starter if something goes bad and you need to shut it down immediately.

lazyuniondriver wrote:I highly discourage people from starting equipment from standing on the ground. There are way too many safety issues invoved from cranking or starting motor equipment from anyplace other than the operators seat

That is why we encourage folks to always shake the stick before you pull that starter. Ensuring that the tranny is in neutral is the safest way to ensure the tractor does not move on you when you start it. Starting early Cubs from the operator's platform may not always be possible.

lazyuniondriver wrote:I would have a lanyard on it to break the circuit from the operators platform if an emergency arose

Thank you, I didn't think about that. It doesn't, but it will before I use her again.

I do "shake hands with the shifter" before starting. Learned to do that at the age of 10, whether sitting in the seat or not.

Good news. I got the tractor started. Thank you to all who offered suggestions as to what might be the problem.

In case anyone is interested, I will describe briefly what I did.

1) Put a jumper wire across the two terminals on the back side of the ignition switch, to by-pass the switch, just in case the switch was defective. Result: tractor would not start. Conclusion: switch is not the problem.
2) Ran a jumper wire from the negative terminal of the battery (tractor is positive ground) to the ignition coil (the coil terminal that is not connected to the distributor). Result: tractor would not start. Conclusion: wiring between switch and coil is probably not the problem.
3) With the jumper wire from the battery still in place, I pulled the wire out of the tower on the ignition coil and stuck another piece of wire into the tower. I held the other end of this wire near the frame and turned the engine over. Result: no spark visible.
Conclusion: maybe the ignition coil is bad?
4) I tested the ignition coil for resistance 3 ways: Resistance of primary circuit (from + to - terminal) was 0.9 ohm. Not bad.
Resistance between tower terminal and either + or - terminal was about 8800 ohms. Not bad either. Resistance between case and + or - terminals was too high to measure, as it should be. Conclusion: ignition coil is not the problem.
5) At this point, I was beginning to think the distributor was the problem (points, condenser, rotor, etc.). But before opening up the distributor, I decided to clean up the connections at both ends of the little wire connecting the side of the distributor to the terminal on the ignition coil. When I re-connected the wire, I checked for spark coming out of the tower on the ignition coil, and voila! Beautiful hot sparks! I put the wire back into the tower on the ignition coil that connects it to the distributor and tried to start the tractor. It started right up and ran perfectly.
6) I did notice that the stud on the side of the distributor that the little wire connects to was a little bit wobbly. Is this normal? Is it likely to cause me further problems at some time in the future?

Now I have another question: if the connections between the side of the distributor and the terminal on the ignition coil are dirty (and they were), will that result in a "no spark" situation? I don't know enough about ignition systems to know the answer. Does "no spark" make sense in a situation like that?

Thanks again for all of your help.

Dave50cub wrote:The stud on the side of the distributor that the little wire connects to was a little bit wobbly. Is this normal?

Should be snug/tight.

If the connections between the side of the distributor and the terminal on the ignition coil are dirty (and they were), will that result in a "no spark" situation?

Dirty no problem. Corrosion a problem.

Excellent job of troubleshooting. You can see not following through each component system before moving to the next is a recipe for multiple failures when only one failure caused the breakdown.

Always remember on a battery ignition system, the distributor contains the parts of two separate systems which must be examined separately one before the other.

First, check the spark generation system and related components. When you are satisfied a good spark is being produced, move to the spark distribution system and its related components, rotor, cap, wires, and plugs.

If you break a breakdown into small pieces, you will have your tractor up and running in no time at all.

Dave50cub wrote:6) I did notice that the stud on the side of the distributor that the little wire connects to was a little bit wobbly. Is this normal? Is it likely to cause me further problems at some time in the future?

Sometimes the insulator for that stud can break causing a short from the coil resulting in a no spark situation. Make sure the stud is tight and the insulator is in one piece.