Voltage to points

[40cpe]

I have a converted chevy distributor in my 8BA. After 3-4 thousand miles the contacts look rough. I filed/reset them and it's running good again. Wondering why they didn't last, I went to looking for the reason. I have a 1.8 ohm ballast feeding a flame Thrower 1.5 ohm coil. On a 12V system I have 5V at the coil, key on, points closed. Running I have 11 volts on the input to the coil and 8.2V on the distributor terminal of the coil with the alternator charging at 14.4 volts. Reading comments on this forum directed at 6v systems, I see 4v is recommended. I've Googled a good bit and can't find any info on voltage to the points. I'm looking for help to determine if I need more resistance, or if I just have crappy points. The ones in the distributor are Delco. Thanks for your guidance.

[JSeery]

Originally Posted by 40cpe

I have a converted chevy distributor in my 8BA. After 3-4 thousand miles the contacts look rough. I filed/reset them and it's running good again. Wondering why they didn't last, I went to looking for the reason. I have a 1.8 ohm ballast feeding a flame Thrower 1.5 ohm coil. On a 12V system I have 5V at the coil, key on, points closed. Running I have 11 volts on the input to the coil and 8.2V on the distributor terminal of the coil with the alternator charging at 14.4 volts. Reading comments on this forum directed at 6v systems, I see 4v is recommended. I've Googled a good bit and can't find any info on voltage to the points. I'm looking for help to determine if I need more resistance, or if I just have crappy points. The ones in the distributor are Delco. Thanks for your guidance.

Maybe a capacitor issue? You should have plenty of resistance with a 1.5 ohm coil and 1.8 ballast resistor! Are you sure on the coil resistance? Did you measure it?

[40cpe]

I did measure it, with a Fluke meter. It read 1.4 ohms.

How do the voltages at the coil and points look?

[Jack E/NJ]

Agreed on a potential capacitor issue. Sounds like the ballast is about right for a 1.5 ohm coil. With the points closed, there should be 1.5/3.3 x 12.8v = ~6v at the coil input with points closed not running. So 5v sounds about right if the battery was a bit low and some resistance thru the ign switch. When it's running, who knows what you'll get especially with a slow responding digital meter. Jack E/NJ

[40cpe]

Resting battery voltage was 12.3v. With key on, points closed battery read 12.1V. The 5v at the coil was taken using a cheap analog meter and a digital meter. So the capacitor could be responsible for the 11V reading at the distributor terminal? What would be the desirable reading?

[tubman]

Sponsored Links (Register now to hide all advertisements)

Rapid deterioration of the points can be caused by a condenser that is waaay over or under capacitance. Unless you have a proper tester, the easiest thing to do would be to swap in a good condenser. Unfortunately, that is easier said than done with the quality of condensers available today, you might just get another bad one. If it runs well with one, keep it and check the point life. You might get lucky.

[koates]

The test that you really need to do is the current draw (in amps) of the coil with the engine running. That reading should be around 3 amps or less. If its higher than that then there is the answer to why your points are not lasting. The condenser is very important and could be the problem. Most people have no means to test a condenser correctly so just fit a new one. You talk about voltage to the points but that is not something that can be tested normally. Only test voltage on the ignition supply to the coil. The 4 volt recommendation coil input is suggested only for 6 volt original Ford bakelite coils . I would suggest that the input voltage on your coil with engine running should be around 7 or 8 volts and not 11 volts that you are reading. Check the coil amps draw running and report back. Dont forget a small amount of high temp lube on the dist cam. Regards, Kevin.

[40cpe]

I have another capacitor I'll try and see if it changes the voltage to the points.

Thanks for the direction, I hadn't suspected a capacitor issue.

[40cpe]

Thanks Koates, I'll get that reading tomorrow before changing the capacitor.

[JSeery]

We often talk in voltages, maybe because it is easy to check, but current (amps) is what is important here and your looking for about 3 to 4 amps. The capacitor is not going to change any voltage, resistance or amperage readings you take, but a proper capacitor is going to have a big impact on points wear.

[40cpe]

I tried to check the running amps at the coil with an older Craftsman clamp type digital DC amp meter and it just jumped around between 1 and 3 amps. I then used a harbor freight digital meter in series with the coil feed wire and it varied between 5.8-6.25 amps. I don't know if I should trust either of the readings. If someone can recommend a meter we can trust that won't break the bank I'll order it.

[Jack E/NJ]

I'd trust ohm's law in the total 1.8 + 1.4 = 3.2 ohm resistance measurement. So max possible current = 14.4/3.2 = 4.5 amps running. Jack E/NJ

[40cpe]

Jack, thank you for that perspective and it certainly makes sense. Those readings were close to the advertised values for the ballast and the coil and what I got from checking with a Fluke meter. This Fluke just doesn't have a provision for measuring DC amps.

If 4.5 amps is acceptable, then I'm back to just replacing the points and condenser hoping to get a better quality?

[tubman]

It seems these days that it's always a "crap-shoot".

[Jack E/NJ]

tubman>>>it's always a "crap-shoot".>>>


Always? Even your trash cans? 8^) Jack E/NJ

[koates]

Use an older analog ammeter and see what you get. Cheap digital meters do not always work very well on old cars unless it is a higher quality Fluke or such. I think 4.5 amps is on the high side and would be good at around 3 amps. Many cars I have tested are down towards 2 amps with the engine running. Engine running with the points rapidly closing and opening the circuit regulates the current to that lower figure. The higher the current draw the quicker the contacts burn out. Why do you need a FLAME THROWER coil? Half of its potential output would never be used on your engine. Use a standard ignition coil. Regards, Kevin.

[tubman]

Originally Posted by Jack E/NJ

tubman>>>it's always a "crap-shoot".>>>


Always? Even your trash cans? 8^) Jack E/NJ

I was referring to buying parts at your "FLAPS". Although one of mine would be a solution to the OP's problem, they are a specialty item, and therefore a little expensive. Plus, there is the added complication of mounting it externally on the SBC distributor (depending on the type used).

That being said, look at the date on the picture; several hundred out there since then with no reported problems. I'd do it, but that's just me.

Thanks for the recommendation, Jack.

[rotorwrench]

I remember the aftermarket stuff for the GM window type distributors were an integral point & condenser set and they were crap back then. I generally suggest purchasing Echlin brand stuff from Napa but they are now under the Standard Motor Parts banner and may suffer quality issues due to that. I always buy at least two at a time and check to see if I get any arcing on the points when I turn the car over with the cap off and a test plug plugged into the coil tower. If it's bad it will arc a lot. A good one should arc very little or not at all. The spark from the test plug should be consistent too.

[Jack E/NJ]

tubman>>> Plus, there is the added complication of mounting it externally>>>


I've always considered them an extra added attraction. The only complication is they occasionally need a maintenance buff to show off their hidden beauty . 8^) Jack E/NJ

[40cpe]

Originally Posted by koates

Why do you need a FLAME THROWER coil? Half of its potential output would never be used on your engine. Use a standard ignition coil. Regards, Kevin.

I had a Pertronix unit in the distributor at one time using this coil. The name doesn't mean anything, just the ohms. I have a few more coils on the shelf, one being an old Ford yellow top coil, and none have any more resistance. I don't understand why I'm getting such high amps using the often recommended resistance. It seems like any change I make will take a good while to show the results in points life.

[JSeery]

Originally Posted by 40cpe

It seems like any change I make will take a good while to show the results in points life.

Yep, but it doesn't affect much but the rate of wear on the points.

[tubman]

Originally Posted by Jack E/NJ

tubman>>> Plus, there is the added complication of mounting it externally>>>


I've always considered them an extra added attraction. The only complication is they occasionally need a maintenance buff to show off their hidden beauty . 8^) Jack E/NJ

Yeah, it's a good "fake-out". When we were high school kids, we used to buy the originals at "The Big Wheel" speed shop on Lake Street in Minneapolis, mount them on the outside of the stock distributors in our cars, and tell everyone we had a "Mallory Racing Ignition".

I think they were $3.85 back then.

While we were at it, we'd strip the paint off of the top tank of the radiator and hit it with that same "Brasso". That brass sure took a good shine, but became another maintenance item.

[koates]

Originally Posted by 40cpe

I had a Pertronix unit in the distributor at one time using this coil. The name doesn't mean anything, just the ohms. I have a few more coils on the shelf, one being an old Ford yellow top coil, and none have any more resistance. I don't understand why I'm getting such high amps using the often recommended resistance. It seems like any change I make will take a good while to show the results in points life.

Swap the Flamethrower coil for your yellow top Ford coil. Those yellow top coils are excellent coils and long lasting as well. My 1970 Ford Falcon 302 V8 still has its original yellow top fitted and never a problem. The original resistor with these was a special wire built into the wiring loom. Regards, Kevin

[40cpe]

Originally Posted by koates

Swap the Flamethrower coil for your yellow top Ford coil. Those yellow top coils are excellent coils and long lasting as well. My 1970 Ford Falcon 302 V8 still has its original yellow top fitted and never a problem. The original resistor with these was a special wire built into the wiring loom. Regards, Kevin

I don't mind swapping to the Ford coil, but the resistance measures the same. Do you have the resistance value of the wire feeding your Falcon coil?

[koates]

Originally Posted by 40cpe

I don't mind swapping to the Ford coil, but the resistance measures the same. Do you have the resistance value of the wire feeding your Falcon coil?

I knew you would ask me that. I grabbed my 1970 Falcon factory shop manual genuine one and here are some useful specs for you. Coil primary resistance is 1.40 to 1.54 ohms. Secondary resistance is 8000 to 8800 ohms. Current draw engine stopped is 4.5 amps. Engine at idle speed is 2.5 amps. Primary circuit resistance wire resistance is 1.30 to 1.40 ohms. All tests were at 75 deg F. So therefore your total primary circuit resistance should be approx 3 ohms. Condenser is .15 to .20 mfd. All official FORD MOTOR Co Specs. Hope this will help you. Regards, Kevin.

[40cpe]

Sponsored Links (Register now to hide all advertisements)

Thank you for the very helpful information. We all seem to be on the same page as far as the amount of resistance. I'm going to order a Fluke multimeter that will measure up to 10 amps and try to reconcile ohm's law and the reading I get. Thanks to everyone who has contributed.

[koates]

Most work I do on older cars (pre 1975) I use an old automotive test set which consists of two meters. A voltmeter analog type with 3 scales and a pointer which measures DC volts from 0 to 50 volts. An ammeter analog type which measures 0 to 60 amps. It also measures minus 10 amps. The set also has a variable rheostat which can simulate various battery conditions. It was made for testing and adjusting generators, alternators and voltage regulators. It is more suitable than many digital meters which tend to jump around on their readings because of the radio frequencys that old cars tend to transmit into the atmosphere. El-cheapo digital multimeters are useless on old cars. Regards, Kevin.

[1948F-1Pickup]

An original Ford yellow top coil would be ok. The offshore-manufactured reproduction item is pretty much junk though.....

Ignition Points in 2020 are perplexing to me. Seven vehicles here and nothing has points in it. On the truck, I couldn't even get to that window on the distributor cap anyway. Literally anything inside the distributor is better than points in my opinion.

[Scotty's 52 F3]

I converted a chev Accel dual point to replace my Load o Matic a few years ago. Used a Bosch blue coil as suggested here on the barn, recurved it as suggested and haven't touched it since.

I should probably hit Tubman up for his condenser so I have it when I need it.

[koates]

Originally Posted by 1948F-1Pickup

An original Ford yellow top coil would be ok. The offshore-manufactured reproduction item is pretty much junk though.....

And what brings you to the conclusion that the repop ford yellow top coils are pretty much junk ? Just heresay or actual experience. Not a good idea to spread unconfirmed rumors. I have one of those repop yellow tops on my 66 mustang and it has been fine for eight years and with plenty of driving too. Regards, Kevin.

[Tinker]

makes sense a yellow top would work on a 12volt system with just a ceramic 6v resistor. As they kept the points and dizzies 6v on early yblocks and used a yellowtop coil.

[BUBBAS IGNITION]

Been reading this post and trying to stay away.......

After training techs for over 30 years i have a lot to say :

There are some good comments in the thread
1=ford yellow top is a great coil and very stable with resistance values

2=pertronix coils are off shore and the cheapest coil money can buy , dont maintain resistance very well .......

3= 12 volt current is between 3-4 amps and that will work very well

4= a 1.5 ohm coil and a 1.5 ohm resistor is good , so 3 ohms divided in to 12 volts gives a current flow of 4 amps

5=no one has discussed voltage drop , so lets say battery is exactly (it isnt) 12 volts then the ressitor should drop the voltage 1.5 ohms x 4 amps = voltage drop of 6 volts then the coil is 1.5 x 4 amps = 6 volt drop so i theory the coil and resistor drops the entire 12 volts with very little going across the contacts. (perfect world ) but the battery is more than likely 12.2 volts which would leave .2 at the points .
PERFECT !!!

Now start the car and the battery goes to 13-14 volts , the excess volts or lets say 14 volts then the increase has got to be asorbed by the resistor and the coil .

The most important wire in the system is the calibrated wire going from the coil to the distributor (usually a finely stranded lead wire designed to drop the excess voltage from the coil negative )

[40cpe]

Following up on this thread: I have gotten a good education on ignition resistance theory from all you good folk's comments and facts. In looking for an amp meter I could depend on, on ebay I found a Weston 10 amp meter from what appears to be an industrial panel. I got it for cheap, so I bought it as a special purpose tool. So using a 1.8 ohm ballast resistor and the 1.4 ohm coil on a 12.3V battery, the meter shows ~ 3.6 amps engine stopped and 2.1 amps engine idling. From what you are telling me, it is about perfect. I will now buy a better set of points (I hope) and get on with life. By the way, I found the resistor increases to ~ 3.2 ohms after running a little while. Thank you all for your very helpful information.

[koates]

40cpe, YEP, you seem to have it all correct now. The current draw in the coil primary circuit is most important ,but most guys just overlook doing those tests. When the resistor is cold and its ohms resistance is low that allows for a higher voltage at the coil for cold starting and when the resistor warms up (ohms increases) the voltage is reduced at the coil for hot starting and also allows a longer point life because of reduced current draw. Make sure you align your contacts perfectly parallel to each other so they have a long working life. You are good to go. Regards, Kevin.

[G.M.]

Almost all condensers will read good cold. You need to heat
them to 250 degrees and test them. When Skip rebuilds a
coil he asks the customer to send a few condensers so he
can hot test them. ALL stock new or used old Ford coils get
real weak when they get hot and come back to life when
they cool down. I have mounted small fans blowing cool air
on the coil which helped. Skips rebuilt coils run good when
hot. Skip puts a full 6 volts or higher on a coil to heat them
up until you can't pick them up and after his rebuild still work.
He has been rebuilding coils for well over 20 years and NEVER
charged to repair one that failed, except ones that left the
ignition switch on. If the points are open this is not a problem.
But if the points are closed the windings are like a resister and
get very hot. This melts varnish off the wire in the coil and shorts
the winding you will even have the potting material melt, xpand
and crack the case. Skips coils are insulated with an epoxy on
the wires and can take higher temps. Maybe installing a small
pilot light that is on when the ignition switch is on will save a lot
of coils. A small LED will work. You don't want much over 4.0 volts
to the coil on 6 or 12 volt systems or you will arc the points. G.M.