Burning points

MSD

Well-known Member
What is causing the points to burn so quickly in a G JD distributer? It has an MSD coil (but no box) and a new set of points and condenser. After running for less than 5 minutes it started missing and the points contacts were smoky white looking. Would to hot of coil cause it, or a bad condenser maybe? It has new plugs, cap and rotor, good wire spark plug wires also.
 
Usually if contacts are burning and pitting it is a bad condenser, or at least that has been my problems.
 
"Would to hot of coil cause it"

What matters is the coil's internal primary resistance and the resulting primary ignition current.

Can you measure the primary current, points closed, ignition "ON", engine NOT running?

Current in the 3-4 Amp range is desirable, some say up to 5 Amps, in my experience when you get over 4 Amps point life decreases literally exponentially.

If the condenser is out of range, one point will pit and the other get a buildup of material... is this happening on your tractor?
 
Bad condensor, to much grease on rubbing felt, loose connection, incorrect point gap, worn shaft bushings, engine not grounded.Mismatch of condensor value.Check point aligment to each other .Breaker arm must be free on pivot pin and not binding.If the pivot pin itself is worn it causes the points to break slowly instead of cleanly and points will burn.
 
Too much voltage to the points when running. 12 volts is fine for starting,but should drop back to no more than 6 volts running. Internal resistor coil?,or auxiliary resistor ahead of coil?
 
Sorry (not a flame) there is no such modern coil with a resistor inside. They are just wound vor the correct voltage, like a 12 volt electric drill is great on 12v, but heats and draws too much amperage when using 24volts. Jim
 
Some, not all, after market high energy ignition coils have less then the typical stock 3 ohms (yields 4 amps coil current on a 12 volt system) of LV Primary winding resistance. If that's the case the points are switching excess current and they will burn up prematurely. Often an elec switch box ignition is used which is designed to handle more then the typical 4 amps and they use a high energy coil and get a higher energy spark. A bad condenser also contributes to premature points failure. Id check the coils LV primary (+ to -) resistance. If its way less then 3 ohms thats why points fail prematurely.

John T
 
new china points will burn in a heart beat.. cheap contact material. The good ones have tungstun coating on them. A he coil will also burn it. as others have said.
 
JohnT,
How can anyone with today's cheap EVOMs measure resistance accurately, you can't zero them? Short the leads together and they always show a few ohms, not zero. I remember you could zero the old analog ohmmeters, but ohm scale was the least accurate of all the scales. As a student working at USNAD crane, I used to calibrate them. Not sure, been a long time ago, but weren't thay only 5% of the full scale reading? Or something like that.


You and Guido may have the last two with working simpson 260 in existence, well I'm sure some one else will tell me I'm wrong. BYW, wasn't Columbus the first to bring 260s to this country?

That said, why not just measure the primary current? Even my cheapo, FREE HF meters, are more accurate measuring current vs ohms.
 
Question - did you clean them before installation?
An obvious question, but people have been caught before with that issue after fitting the points with the protective film still on them.
Just a question
Rx
 
"JohnT,
How can anyone with today's cheap EVOMs measure resistance accurately, you can't zero them? Short the leads together and they always show a few ohms, not zero. I remember you could zero the old analog ohmmeters, but ohm scale was the least accurate of all the scales. As a student working at USNAD crane, I used to calibrate them. Not sure, been a long time ago, but weren't thay only 5% of the full scale reading? Or something like that.


You and Guido may have the last two with working simpson 260 in existence, well I'm sure some one else will tell me I'm wrong. BYW, wasn't Columbus the first to bring 260s to this country?

That said, why not just measure the primary current? Even my cheapo, FREE HF meters, are more accurate measuring current vs ohms. "

The currently popular digital multimeters like the HF yellow or red that cost $5 for most folks, do not zero like the old analog meters nor do they have 10k ohms/volt of source impedance. The lead resistance is like 4 tenths of an ohm. Big deal on anything but a ballast resistor on a tractor ignition system. But if you know what it is, it's still no big deal and you can read them down to 2 decimal places.....try that with a Simpson or Fluke......depends on which side of the meter your eyeball is located.....so they put a mirror behind the needle and turn it sideways to take out some of the guess work. Must have weighed 5 lbs too; the HF you don't even know it's in your tool bag. HF meters also have megohms worth of impedance in the front end so the meter doesn't load sensitive circuits like the volt-ohm Simpson or whatever and you don't wrap the needle around the stop peg if you screw up and select the wrong scale or wrong function. You don't have to find a Vacuum Tube Voltmeter to measure them...which does have a zero for the voltage.

Yeah times past were really great......right along with convergence circuits on color tvs and points and condensers for spark generating circuits, and coughing, raw gas belching Quadrajet carburetors and exhaust manifold heat risers that always stick closed and carbon steel exhaust systems, and body panels with no protection from salt and on and on. Yeah life was great back then.
 
I am a retired electronic technician, and from my personal observation over the last 45+ years, the cheapest meter made to day is as good or better for accuracy than the best one made 45 years ago. They may not be as durable, but for the price who cares. By the way, I also have a Simpson 260 I still use on a regular basis.
 
Texasmark1
So am I right about EVOM's are not very accurate when measuring resistance, you can't adjust the zero? So why not just measure the current and adjust the ballast to get 4 amps?

Some day I plan to measure the current and the voltage used on my Jubilee's coil. When I do, I'll post back.

As far as the ohms per volt, is that really an issue when working on cars and tractors?

The old school analogs were around 20K/volt, 50 ma meters. They worked just fine as long as you didn't try to measure 220v on the ohm scale. Or get the polarity reversed when measuring DCV.
 

Had similar problem on a 2010 and it was a bad switch. I can't tell how to check that, and yes, I know the 2010 was at least 10 years newer.

KEH
 
Just measure the amp draw :idea:

Are pay's yer money..


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(quoted from post at 11:46:09 07/25/15) What is causing the points to burn so quickly in a G JD distributer? It has an MSD coil (but no box) and a new set of points and condenser. After running for less than 5 minutes it started missing and the points contacts were smoky white looking. Would to hot of coil cause it, or a bad condenser maybe? It has new plugs, cap and rotor, good wire spark plug wires also.

Some of those super duper whiz bang unltra turbo mega blaster coils have a 0.7 or even 0.5ohm primary. To spark a 9000rpm, 20psi boost V8 operating on methanol.
There is nothing that you can do to a 975-1500rpm two cylinder spark ignition system that a boring every day Napa 12V, 3.5phm coil can't ignite.
At most it needs is a Pertronix or pertronix II module and a stock coil..
 
(quoted from post at 22:07:10 07/26/15)
(quoted from post at 11:46:09 07/25/15) What is causing the points to burn so quickly in a G JD distributer? It has an MSD coil (but no box) and a new set of points and condenser. After running for less than 5 minutes it started missing and the points contacts were smoky white looking. Would to hot of coil cause it, or a bad condenser maybe? It has new plugs, cap and rotor, good wire spark plug wires also.

Some of those super duper whiz bang unltra turbo mega blaster coils have a 0.7 or even 0.5ohm primary. To spark a 9000rpm, 20psi boost V8 operating on methanol.
There is nothing that you can do to a 975-1500rpm two cylinder spark ignition system that a boring every day Napa 12V, 3.5phm coil can't ignite.
At most it needs is a Pertronix or pertronix II module and a stock coil..
hat is right! Put that bad a$* MSD 0.7 Ohm coil on there & it will eat points faster than a stump grinder!
 
I wouldn't call the lead resistance a measurement error as it's common practice to "zero the meter" prior to measuring as zero was highly dependent on the voltage of the internal battery to operate that 50 ma meter. Since current technology is digital, unless the battery has just crapped out, you have no measurement error as such. Since there is no knob to turn, you just record the "offset" in your brain when making resistance measurements and besides, once you get over 100 ohms, what's .4?

They were 20k on the DC scale but 10 on the AC scale. Course AC was usually used for power line measurements with zero source impedance, so to speak, so it didn't matter. Other thing was the measurement accuracy was like +/- 5 to 10%, probably due to the resistor types used in the internal voltage dividers or the D'Arsonval meter movement itself. The HF uses 1% or better Metal Oxide resistors which are resistant to moisture intrusion which the old Carbon Composition weren't and changed value with age due to absorption.

No! On the issue with input impedance of the meter and your tractor.

I do recall mentioning errors in measurement methodology as a problem in the Simpson and other Scalar instruments.
 
(quoted from post at 03:33:11 07/27/15) I wouldn't call the lead resistance a measurement error as it's common practice to "zero the meter" prior to measuring as zero was highly dependent on the voltage of the internal battery to operate that 50 ma meter. Since current technology is digital, unless the battery has just crapped out, you have no measurement error as such. Since there is no knob to turn, you just record the "offset" in your brain when making resistance measurements and besides, once you get over 100 ohms, what's .4?

They were 20k on the DC scale but 10 on the AC scale. Course AC was usually used for power line measurements with zero source impedance, so to speak, so it didn't matter. Other thing was the measurement accuracy was like +/- 5 to 10%, probably due to the resistor types used in the internal voltage dividers or the D'Arsonval meter movement itself. The HF uses 1% or better Metal Oxide resistors which are resistant to moisture intrusion which the old Carbon Composition weren't and changed value with age due to absorption.

No! On the issue with input impedance of the meter and your tractor.

I do recall mentioning errors in measurement methodology as a problem in the Simpson and other Scalar instruments.
ome on!!!! This thread is about burning points! If you want to jawbone forever about your old time meter BS, go to a meter forum! :roll:
 

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