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whats burning my points?

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430
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PostPosted: Thu Dec 27, 2012 1:50 pm    Post subject: whats burning my points? Reply to specific post Reply with quote

I bought this 430 that has been converted to 12 volt not running. We rebuilt the carb, put new plugs, wires, cap rotor,condenser, and points on it and it fired right up. Ran good. Ran it around for about 20 minutes and it started to spitt and sputter and run like crap. Checked the points and they were burnt again. So, bought more points, another resister, thinking that might be it, and burnt them again. Bought another set and a coil with the resister in it and it is running longer, but starting to do it again. Is there something I'm missing? Could it be something to do with the alternator? That's the only thing I haven't messed with.(ammeture doesn't work.
 
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buickanddeere
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PostPosted: Thu Dec 27, 2012 2:12 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

No 12V coil has a resistor in it.
There are either wound with a 1.5 to 1.8 ohm primary for 6V or a 3 to 4 ohm primary for 12v.
The burned points are due to high current from running a 6V coil on a 12V system.
Measure your coil's primary resistance.
 
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430
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PostPosted: Thu Dec 27, 2012 2:42 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

It 3.2-3.3. I've never messed with this 6 to 12 volt stuff. What do i need to do to make it run? I do have the other coil that reads 1.5 in a box.
 
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John T
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PostPosted: Thu Dec 27, 2012 2:53 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

A couple things (among others I can post if needed) that can cause premature points burning up are:

1) Weak or Open or not connected or way wrong sized Condensor

2) Excess (too much over 4 amps) coil current caused by:

a) Wrong coil (like a 6 volt coil on a 12 volt system with no external series voltage dropping (12 to 6) ballast resistor)

b) If its a 12 volt tractor and you have a 6 volt coil buttttttttttttt theres too low ohms of ballast. Ballast ohms is near what the coil LV primary ohms is i.e. maybe in the range of 1.25 to 2 ohms.

On a 12 volt tractor you need EITHER

A) A 12 volt coil which may be labeled "12 volts" or "12 volts NO ballast required"

ORRRRRRRRRR

B) A 6 volt coil PLUS an external series voltage dropping (12 to 6) Ballast Resistor

NOTE if the points are having to switch too much over 4 amps of coil current they WILL BURN UP TOO FAST. In order to limit points current to 4 amps on a 12 volt tractor the TOTAL (coil PLUS any Ballast) primary ignition resistance needs to be around 3 ohms as 12/3 = 4 amps

SOOOOOOOOOO insure coil is a "12 volt" or "12 volts NOT for use with ballast" (around 2.5 to 3+ ohms) or if its a 6 volt coil (around 1.25 to 2 ohms) theres sufficient ballast resistance.

NOTE Im talking typical old tractor stock coils here NOT high voltage or high energy or after market or super coils or Accell or Mallory types etc OLD STOCK FARM TRACTOR COILS FOR POINTS IGNITIONS

NOTE if coil is labeled "12 volts for use with or requires ballast" its in reality more like a 6 volt coil and it means what it says BALLAST REQUIRED or esle it will overheat and points burn up fast

Got it??? If I missed anything the other fine gents can add to this

PS Contrary to what most lay persons believe you likely will NOT find a typical old 40's 60's vintage tractor coil that has a stand alone discrete "RESISTOR" tucked away somewhere inside the can.....X Ray or disect one if you like, I bet theres no compartment or seperate area with a "Resistor" hidden inside. NOTE for those in Rio Linda or no electrical expertise whatsoever or are unfamilair with electronics terms and components, A ResisTOR has ResistANCE and wire has some slight ResistANCE butttttttttt a wire is wire and resistORS are resisTORS, if you go to Radio Shack and ask for resistors they wont show you wire and if you ask for wire they wont show you resistors lol

John T
 
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MSD
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PostPosted: Thu Dec 27, 2012 3:21 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Did I read once if you have the polarity wrong on the coil it will cause points to burn also?
 
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cole in mo.
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PostPosted: Thu Dec 27, 2012 4:25 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Is the exciter wire to the alt hooked to one of the small posts on the coil, if so which one. It should be hooked to the same one comeing from the switch. But the alt may have a short in it feeding 12 volts back to the coil, and into the points. You may need to put a one way diode in the exciter wire.
 
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John T
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PostPosted: Thu Dec 27, 2012 4:49 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

If coil polarity is reversed it will still spark but the spark is weaker and the ignition system isnt as efficient with more heat losses, and the coil has to work a bit more as the voltage has to ramp up slightly higher. It doesnt affect coil current or points life to any major extent, however.

John T
 
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Ben.So.Tex
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PostPosted: Thu Dec 27, 2012 6:29 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Put a resistor in line before coil. Had this happen to me on a ford I converted and the points would burn up in about 2 min of starting engine. Good Luck
Ben
 
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MSD
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PostPosted: Thu Dec 27, 2012 8:35 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Thanks John, wasn't sure if that is what I had read or remembered.
 
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MrJDMan80
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PostPosted: Thu Dec 27, 2012 9:48 pm    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Had one cone through the shop a few years back that had the alt wire hooked to the coil. It did this as well but would cook the points even with the tractor off. Found the trigger wire on the coil was hooked to the correct side for power, but that was after the resister. Took it off and put it on the powered side of the resister and added the missing diode. Problem solved. Thinking back, I don"t know how the tractor ever shut off being hooked up like that.
Tim
 
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John T
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PostPosted: Fri Dec 28, 2012 5:15 am    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

So theres two of us with that problem lol lol

The DC LV Primary winding resistance (like 3 ohms) is the same regardless in which direction current flows through the coil....and the coil current is the current the points have to switch on and off and on and off,,,,,,,,,,

John T
 
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buickanddeere
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PostPosted: Fri Dec 28, 2012 6:05 am    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

It should work fine. The problem must be with the point gap. Cam lobe, oil, grease or dirt.
 
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Machinery-Man
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PostPosted: Fri Dec 28, 2012 8:27 am    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

Most everything has been covered in one form or another but your problem is excess voltage. I ran a 430 on 12 volts but used a 12volt generator. Those mismatched systems have to be properly switched and regulated with an alternator but you have excess voltage to the points. A resistor block is needed and I would put it at the coil.
 
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buickanddeere
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PostPosted: Fri Dec 28, 2012 8:43 am    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

A 3.0 to 3.5 ohm coil on 12V should limit primary current to 4 amp which is about max for points.
An ammeter needs to be used to verify primary current. Or this guy is just going to continue ramdonly swapping connection and components.
Is the distributed bushing work and affecting point gap?
I'm also suspicious that the condensor/capacitor is open or under sized.
Next question. Why convert a 40/420/430/440 gas to 12V ? They always started well if in tune.
 
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M-MAN
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PostPosted: Fri Dec 28, 2012 9:45 am    Post subject: Re: whats burning my points? Reply to specific post Reply with quote

The alternator is wired wrong & possibly bad as well.

The wrong coil, ballast resistor, etc won't kill the points in 20 minutes of run time. 12 volts will kill them but it takes a lot longer than that to kill them & it's starting and stopping that does the damage.

My guess is your alt is being fed straight from the coil with no diode to prevent backfeeding. It's either burning them at shutdown because of that or you're backfeeding the coil way more than 12 volts from that alt.
 
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