Resistance of Ballast Resistor on old Points ignition

Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).

 

[Rheilly Phoull]

On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:

Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).

Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

 

On Wednesday, 27 March 2019 22:20:05 UTC, tub...@myshop.com wrote:

Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).

A few ohms is about right. It would never work with 1k.


NT

 

[Rheilly Phoull]

On 28/03/2019 8:23 am, Rheilly Phoull wrote:

On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:
Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).


Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

I also assume you know that the ballast resistor is used to apply a
higher voltage to the coil by bridging it on start then opening the
bridge when running.

 

[Dave M]

Rheilly Phoull wrote:

On 28/03/2019 8:23 am, Rheilly Phoull wrote:
On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:
Does anyone know the correct resistance of the ballast Resistor on
old Points ignition? I have an old Farmall M tractor. That resistor
(which is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I
got about this tractor says the voltage should be about 8 volts
after the resistor. I dont know how much tolerance is allowed, but
I'd rather see a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have
been a bad condensor (capacitor). But it runs rough after replacing
the points, condensor, plugs, dist cap and rotor. The spark on a
test sparkplug seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they
should be fine, since I dont use the tractor all that much).


Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

I also assume you know that the ballast resistor is used to apply a
higher voltage to the coil by bridging it on start then opening the
bridge when running.

That is correct. The resistor is removed from the circuit while cranking so
the engine gets a hotter spark. The reason? Because while cranking, the
starter takes a huge amount of current from the battery, lowering the
available voltage to the coil. Removing the resistor from the circuit gives
more voltage (and current) to the coil, helping the engine start.
After the engine starts running, the starter is no longer activated,
removing the huge current drain on the battery, raising its available
voltage. Then the resistor is inserted into the circuit in order to reduce
the current through the points, thereby reducing arcing, which can eat up
the contacts rather quickly with high current. That's also the purpose of
the condenser... to help reduce arcing across the points.

Cheers!!
Dave M

 

[John-Del]

On Wednesday, March 27, 2019 at 9:33:46 PM UTC-4, Rheilly Phoull wrote:

On 28/03/2019 8:23 am, Rheilly Phoull wrote:
On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:
Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).


Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

I also assume you know that the ballast resistor is used to apply a
higher voltage to the coil by bridging it on start then opening the
bridge when running.

Back in the 70s, I wired a momentary switch across the ballast resistor of my car and mounted it on the throttle shaft of my carb. At full throttle the switch bypassed the resistor.

Between that and turning the air cleaner cover over, the car broke the sound barrier...

Seriously, it did seem to help at high rpm though.

 

[pfjw@aol.com]

This is NOT complicated.

a) The value is about 1.4 ohms for a 12-volt (nominal) system.
b) 1.6 ohms is usually suggested for a 6-volt system (some older VWs and tractors). But that same 1.4 ohm device will work fine.
c) They carry A LOT of current, and so are usually ceramic devices with substantial connectors.
d) They may be purchased for as little as ~$5 + tax for a generic device that may fit to as much as $20 + tax for a name-brand device that will actually fit.
e) They are still stock items in most auto-supply stores and dealerships.

Peter Wieck
Melrose Park, PA

 

[Rheilly Phoull]

On 28/03/2019 8:07 pm, John-Del wrote:

On Wednesday, March 27, 2019 at 9:33:46 PM UTC-4, Rheilly Phoull wrote:
On 28/03/2019 8:23 am, Rheilly Phoull wrote:
On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:
Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).


Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

I also assume you know that the ballast resistor is used to apply a
higher voltage to the coil by bridging it on start then opening the
bridge when running.

Back in the 70s, I wired a momentary switch across the ballast resistor of my car and mounted it on the throttle shaft of my carb. At full throttle the switch bypassed the resistor.

Between that and turning the air cleaner cover over, the car broke the sound barrier...

Seriously, it did seem to help at high rpm though.

Hmm, the thought of Mr Tubeguy doing rooster tails on the tractor would
be a sight you dont see every day.

 

On Wednesday, March 27, 2019 at 6:20:05 PM UTC-4, tub...@myshop.com wrote:

Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).

Sounds like a question for yesterdays tractor forum
https://www.yesterdaystractors.com/cgi-bin/boards.cgi

George H.

 

One thing people didn't seem to notice about points is that you can't just set the gap. The proper gap changes with wear. What you want is for the points to be closed one third of the time.

The number of cylinders matters not. Look at an old time dwell meter, for an 8 cylinder it says so many degrees, but that is at a certain percent of the scale on the meter. For a 6 cylinder the dwell in degrees also hits the same spot on the meter. For a 4 cylinder, with double the degrees of dwell specified STILL needs to be at two thirds, also the same place on the meter scale.

There are a few ways to measure it accurately. The best is with a scope. Sync it to any frequency that lines up with graticule lines and make the bottom part twice as long as the top part.

Another way is to use a resistor and Zener and first take a DVM reading with the points open, just roll the engine to a spot where they are. Read that voltage, should be that of the Zener. Now start the engine and you should read ONE third of that voltage.

You will have to trial and error it to get them really right. Actually GMs had an Allen screw and a window to allow you to set the points with the engine running. The rest you have to try it over a few times. If the "on time" is too short make the gap smaller, if longer make it bigger.

In MOST cases, over the years the lobes wear down on the distributor shaft. What this means is that a smaller gap will be necessary to achieve the correct dwell (closed) time. (duty cycle actually if you want it that way) When this gets too bad, the points are not opening as far and the arcs will wear them out faster. In the old days I noticed people who had to change their points like every couple of months. The coil wasn't shorted, the ballast was fine, there weren't any fouled plugs. It was that the lobes were work down and every time those points opened and made the spark the arc was worse because the contacts wee not pulling back fast enough.

If you have that problem, say if you find the gap is only 0.008" or something and can't get a new distributor shaft then it can be machined. It takes a pretty good machine to do it, but it is not worth programming a CNC for a one off. You can get a guy to do it with NC, OR find an old timer who really knows what he is doing. I am not good enough with that to do it even when I had the machines that might. I am simply not a machinist. you cold maybe find an auto parts place that does their own machine work, they might be able to do it. Some of them though, their machine shop consists of a big belt sander. Remember how they used to mill cylinder heads ?

Not no more. The aluminum heads these days they just blue it up and lay it on a horizontal belt sander and keep on sanding it until all the bluing is gone. A place like that won't be able to do it. You need a GOOD auto machine shop for this. Racing people. Even though they don't use points anymore they should have the skill to do it. you walk in and say "I want to talk to the oldest guy in the place" and then when you get to him "Id you ever redo a distributor shaft, I just can't get one and this thing is eating points, everything else has been checked, the gap is only 0.0XX at 66% dwell.

Something like that. And don't forget, the manufacturer might surprise you and have the shaft in stock for ten bucks.

 

>"Presumably you know ohms law, just calculate the value to give the 8 volts after starting. "

That will vary with RPM. It does not only because of more sparks per second, but with cam overlap the effective compression ratio changes. More atmosphere in there means a higher dielectric strength so it needs more firing voltage. That will change the current load on the primary and thus if not a solid voltage of course it will vary. the values they chose for the ballast kinda split the difference. That's why when you put a hot cam in a car you also beef up the ignition system to supply a higher voltage. You usually do the cam for more high end and it will still need enough firing voltage up there.

Yes, I am car people and from the old days. At my Uncle's funeral the picture of his car was bigger than the picture of him.

And that is the way he would have wanted it.

We never looked at any book to setup an engine. There was a 1957 Chevy that would pull the front wheels up in second gear, up to 110 MPH, and there was my cousin's 442 that was made into a 642 with three deuces and Edelbrock which ripped the front bolts out of the seat. Can you imagine that ? Your car is rolling down the road and you are laying down and kinda stuck... I would have liked to have a video of that but not actually be there... He lived though, it took a motorcycle to kill him. Well it was his fault I have to admit. And then there was my 1970 Toronado that ripped the asphalt up off the street, and this other car I forgot what it was exactly but I remember I bought it off of a guy named Dwayne but the title was made out to Dawne. I never got the title in my name, I had spare plates all over the place. Why bother ? When I bought it I told him "OK, just sign the title Dawne". LOL My other Uncle was a notary public and he flipped cars, alot of them. If you have more that like 12 in a year you are supposed to have a dealer's license in this state, but they didn't go in his name. People sold him a car and just signed the title, when someone bought it he just put their name on it and notarized it. Everything he touched turned to gold. And that is only a small tip of the iceberg.

So when it comes to old cars, well...

 

OOPS ! You want the points closed TWO thirds of the time.

 

>" I bought it off of a guy named Dwayne but the title was made out to Dawne. I never got the title in my name, I had spare plates all over the place. Why bother ? When I bought it I told him "OK, just sign the title Dawne". "

Sorry, I forgot to mention why I mentioned that. It was the car in which I got a ticket in Lakewood, Ohio for flying. Apparently they frown on that.

 

On Thu, 28 Mar 2019 09:33:40 +0800, Rheilly Phoull
<rheilly@bigslong.com> wrote:

On 28/03/2019 8:23 am, Rheilly Phoull wrote:
On 28/03/2019 6:20 am, tubeguy@myshop.com wrote:
Does anyone know the correct resistance of the ballast Resistor on old
Points ignition? I have an old Farmall M tractor. That resistor (which
is a large ceramic power resistor), only measures 3 or 4 ohms

I was expecting it to be at least 100 ohms, if not 500 or 1k.
I measured this with nothing connected to it, using an analog
multimeter.

This resistor is between ignition switch and the ignition coil and
points. It drops the 12volts to about 6 volts. Some information I got
about this tractor says the voltage should be about 8 volts after the
resistor. I dont know how much tolerance is allowed, but I'd rather see
a higher spark plug voltage than a lower one.

The tractor now runs, after it failed due to what appears to have been a
bad condensor (capacitor). But it runs rough after replacing the points,
condensor, plugs, dist cap and rotor. The spark on a test sparkplug
seems kind of weak to me.....

Kind of makes me wonder if this resistor needs replacement?

(The sparkplug wires were replaced about 2 years ago, so they should be
fine, since I dont use the tractor all that much).


Presumably you know ohms law, just calculate the value to give the 8
volts after starting.

I also assume you know that the ballast resistor is used to apply a
higher voltage to the coil by bridging it on start then opening the
bridge when running.

This one is NOT wired that way. The resistor is in line with the coil
all the time. The tractor is a Farmall Super M. I just replaced all the
low voltage wires because the old ones were cracking (dry insulation).
Anyhow, it goes from battery to a simple two terminal ignition switch
(push pull type). On to the resistor and to the coil/points. Thats it...

I just replaced everything in the ignition system except the switch. New
low voltage wiring, the resistor, coil, points/condensor, plugs and plug
wires. The stock coil that I bought says "For 6 or 12 volt systems".
"Resistor must be used on 12 volt systems". These tractors were
originally 6 volt. Most are converted to 12 (including mine) these days.

I assume these stock coils are 6v but work on 12v with the ballast
resistor. Without it, I would think the coil would be damaged. But I
like the idea of full voltage at starting. So I may try it. I'd just
need to run another wire from the push type starter switch to the coil.
I may give that a try. (the starter switch is a separate switch from the
ign switch. It's a push buttom spring loaded contacter).

I also have to add a light to the "dash" to remind me the ignition
switch is on. I know that I am supposed to turn off the ignition when
the tractor is off, but if I run out of gas, by the time I get more gas,
the battery is drained because I never remember to shut off that darn
switch. And I imagine that is hard on the coil and points. Possibly why
the old coil was weak and the old resistor was not allowing enough
voltage to the coil.

After changing all these ign parts, it really runs better, but now I
have to rebuild the carburetor. That thing tends to get flakey every so
often. But the tractor is over 60 years old, so it was due for all new
ignition parts, and a carb rebuild. Plus new fan belts are in order
next. They look bad....