8N Electrical Issue

jdschwass

Member
Hey all,

I have an electrical issue and I am looking for some thoughts on a potential cure. Any ideas would be much appreciated.
I have a 1948 8N with front mount dizzy. Mid-summer it began to have intermittent periods of hard chugging, sputter sputter, dead.
Then the next time I would go to use it, it would be fine. It runs my mott mower, so it needs to run well to drive it properly. I cleaned out carb, cleaned plugs, etc, and it seemed to be okay until now. I proceeded to replace the points, condenser, and rotor. I could get it to spark, but seemed intermittent and weak.
As my battery got tired of cranking, I decided to boost with 12 volts, and the tractor started right up. As soon as I take the lead off the 12 volts, the tractor starts to sputter. I can get it to idle on 6 volts, but wont let me rev up. Im thinking there must be some sort of a short somewhere or drain somewhere, but I cant figure out where to look. Rebuilding the distributor didn?t help, plugs are clean, electrical system I redid last year. I swapped coils with my other 8N and no change. I sanded the points in the voltage regulator, and it is charging. I have tried disconnecting the genny, regulator, etc, still nothing. Everything checks out fine, but spark is still weak, and im running out of ideas. 6 volt battery cranks the engine fine, so connection is good. This week I will probably replace plugs just to be safe, and try swapping dist. Cap. Other than that? I have no ideas.
Thanks to any and all words of wisdom.
 
Sounds like what I just went through with my front mount. Try a jumper across the resistor. If it's happy with the jumper, replace the resistor. Don't run it too long that way to save the coil. But it's a cheap test to eliminate the resistor as the source.
 
assuming a 6v square coil?

What resistor are you running?

What's the wiring and connections look like?

Key switch good?
 
Thanks for the replies. It is indeed a square coil. The ballast resistor is OEM from 1948. I have tested across the resistor and it is functioning as a resistor, so I know for certain that there is power going through it. I should check the voltage drop across it again just to be sure it isn't overly resistive.
I rebuilt/repainted this tractor last year. At the time I redid the wiring, and cleaned up every connection to a shine. It ran perfectly after that. There is no signs of corrosion or anything in the connections.
My ignition switch is good, it is a high load aftermarket switch with fuse. I have tested it and confirmed it to be good.

I will try the resistor bypass tonight and see what happens.

Thanks guys.
 
OK, did some troubleshooting: First off, tested resistor, and I am getting 4.6 ohms across it cold, which is in spec. I tried starting it, not luck. I jumpered across the resistor, and she fired up. That being said, I believe I am just treating the symptoms and there is nothing wrong with the resistor. My genny is throwing 7.2 volts at low-mid throttle. The tractor runs without a battery, but doesn't seem to have enough power to rev up. So im thinking the problem has to be after the resistor somewhere? Also when it was running, I am intermittently getting a pretty solid negative charge... which is odd. Any chance there is intermittent loss through the genny? Or possibly back to the starter? Im not really sure where to look now.
Thanks for any ideas.

Jake
 
" I am getting 4.6 ohms across it cold, which is in spec"

No way! Where did you get that spec?

Spec on the OEM ballast resistor is .03 ohms cold & 1.7 ohms red hot.

You do have the OEM ballast resistor & no others, right?
IMG_20140929_102542_438_zpsc6a740eb.jpg

75 Tips
 
The ignition circuit, the charging circuit, and the starting circuit are all separate and independent of each other.
In other words, you tractor will run without a functioning generator (as long as the battery has a charge) or without a working starter. So forget the generator issue for now. There is a problem in your ignition circuit. As Bruce says the resistance of the OEM resistor is less than one ohm. If you tractor runs when the resistor is bypassed, then there is a problem with that resistor.
 
Yes, like mine. All the tests passed, had a spare parts tractor and having tried everything else I could think of, I swapped out the resistor and hasn't had an issue since. Especially since it ran fine with the jumper. For me, that is my new definitive test for a resistor problem. Pretty cheap too.
 
(quoted from post at 20:15:56 09/26/16) Yes, like mine. All the tests passed, had a spare parts tractor and having tried everything else I could think of, I swapped out the resistor and hasn't had an issue since. Especially since it ran fine with the jumper. For me, that is my new definitive test for a resistor problem. Pretty cheap too.
here is iron involved the resistor assy, so rust & corrosion can get you.
 
"that is my new definitive test for a resistor problem. Pretty cheap too."

It's a good test, cheap too. As long as you don't run it too long.
If you run it with no resistor you may burn up the coil and/or points.
 
Ya, just the one resistor on the 6 volt system. I had a very tired night yesterday, and will use that as an excuse for my resistor being "in spec". I agree, that is too high. Not sure where I pulled that number from, but I had been surfing through the web trying to find the correct value...

I will swap the resistor from my other 8N onto this one and see if that solves the problem.

Your help is appreciated. You think you know everything about something until something you don't think you know about breaks... then you have a learning opportunity.

Jake
 
Just to amend to that, my concern is that the resistor is fine, but that by bypassing it, it is compensating for another voltage drain or deficiency in the electrical system. For example, if my plugs were fouled, or points were burnt, then it is possible that bypassing the resistor could mitigate the effects, and make it appear that the resistor is truly bad.... anyways Im just thinking out loud... I will swap it out with a known good one and report back.

Cheers.
 
".. my concern is that the resistor is fine, but that by bypassing it, it is compensating for another voltage drain or deficiency in the electrical system."

While technically possible, I'd say the chances of that are pretty remote given the reading you got at the resistor.

" I will swap it out with a known good one and report back."

I'm guessing that you've never broken a 60+ year old terminal block trying to get it off the tractor.
75 Tips
 
"Does the starter pull so much voltage that the points do not get enough volts?"

Yes, that can happen. Especially on a 6V system. Make sure the
battery is fully charged and all the connections are clean and
tight. Also make sure you're using good cables, 0 gauge if possible.
The normal 12V car type battery cables can cause issues.
 
(quoted from post at 19:12:50 09/27/16) My 8N will only start after I release the starter button. Does the starter pull so much voltage that the points do not get enough volts?
hange "voltage" to "current" and I'll go along with that.
 
6v or 12v?

What you've described is a classic case of low current to the ignition system.

Put your battery on a charger. (see tip # 60)

You need a strong battery to:

1. Close the solenoid

2. Spin the starter

3. Engage the bendix

4. Provide voltage to the coil.

As the battery gets weaker, the first thing to fail is your spark. If the battery is almost totally dead, all you will hear is the solenoid clicking. In addition to charging the battery, chances are you need new cables as well (tip # 41). And, don't forget to clean all the grounds, to include the mating area between the starter & the block. (tip # 36)

The more current you use to spin the starter, the less you have for the ignition.

If none of the above works, do a voltage drop test on the starter; may be time for a rebuild.
75 Tips
 
I have actually built several 8N's, 600's jubilees, 5000's, that's just the Ford's... never had an issue. (I have too many tractors. :)
I bit the bullet, and I purchased a replacement ballast resistor. It is just a generic 0.8 ohm, ceramic, etc.
I installed it via jumpers just to test it out, and the tractor started up. It also allowed me to rev up, which it couldn't do before without 12 volts applied.
So it seems that my problem is solved, I am going to clean all the plugs and finish the wiring tomorrow, then maybe I can bail the hay in my front yard. (it used to be my lawn).
Thanks all for your help. Until next time!

Jake.
 
(quoted from post at 04:17:28 09/30/16) I have actually built several 8N's, 600's jubilees, 5000's, that's just the Ford's... never had an issue. (I have too many tractors. :)
I bit the bullet, and I purchased a replacement ballast resistor. It is just a generic 0.8 ohm, ceramic, etc.
I installed it via jumpers just to test it out, and the tractor started up. It also allowed me to rev up, which it couldn't do before without 12 volts applied.
So it seems that my problem is solved, I am going to clean all the plugs and finish the wiring tomorrow, then maybe I can bail the hay in my front yard. (it used to be my lawn).
Thanks all for your help. Until next time!

Jake.

I must be unlucky. All three 8N's I've restored either had broken terminal blocks or I broke them in removal.

Glad you got it running.

But, you do know that the .8 ohm ceramic resistor is a fixed resistor, right? The OEM ballast resistor is .3 ohms cold and 1.7 ohms hot, meaning you get higher current at start up which is reduced as the resistor heats up. You don't get that with a fixed resistor.
 

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