1972 IH 140 Keeps burning up coils - HELP


Another mowing season is upon me but my 140 only runs about 30 minutes then it just cuts off. The coil is too hot to hold my hand on, and it won't crank back up. If I let sit for about 30 minutes the coil will cool off some and then it will crank and run for a while until the same thing happens again. This has been going on for several years and I need to fix this.

I have changed the alternator, plugs, and coil to no avail. The alternator is putting out a little over 14 V. I can't figure out what's causing this and need some help / ideas.

Is it possible the electronic ignition is crapping out after running for 30 minutes? I have a spare I could install but those things aren't cheap.
 
If it was converted form 6 to 12 volts and you still have the 6 volt coil (but no external series voltage dropping 12 to 6 ballast resistor) THE COIL WILL GET VERY HOT and can eventually fail totally plus the elec switch switch (or old points when used) can go bad.

Do you have a 6 or 12 volt coil????????

If a 6 on a 12 volt tractor, add a series voltage dropping (12 to 6) external Ballast Resistor or else toss the coil and get a new full true 12 volt rated (NO ballast required) coil

Its best to match the coil polarity to your ground. For Neg ground the coils POS wires to ign switch output and its NEG wires to distributor

Questions???

John T
 
HMMMMMMMM some original 12 volt tractors still used a 6 volt coil but somewhere was a ballast resistor or ballast resistive wire or a thermistor wire which still dropped 6 volts leaving 6 on a 6 volt coil. Do you know if the coil is a 6 or a 12 volt???????? If its LV primary resistance between its little + and - terminals is around 1.25 to 2+ ohms its a 6 volt coil, but if more like 2.5 to 3 or 4 ohms its a 12 volt. Perhaps when it was converted from 6 to 12 and ifffffffff indeed it has a 6 volt coil the ballast or ballast resistive wire or thermistor wire may have somehow got by passed???

John T
 
(quoted from post at 15:44:33 03/23/15)
It's a 1972 140 which were factory 12 volt.

The only thing I can think of is whether the coil is mounted horizontally, or vertically. Some coils were made to be mounted one way or the other. Another thing is you might just have a defective coil. Have you tried a different coil?
 
Look at the coil closely. If it says it needs an external resister and you do not have that resister in the system that can cause you problems. Many 12 volt machines still have a ballast resister in the system and if your does not there is where the problem is
 
When the tractor is running how many volts are going to the battery side of the coli maybe your alt is putting too many volts to the coil.
 
Until we know the resistance of the primary winding of the coil we cannot really help you. No such thing as coil with internal resistor anymore. With electronic ignition you need a minimum of 4 ohms resistance weather it is all in the coil windings or in combination of external ballast resistor and coil primary windings.
 
Old is the one that is on track. Look closely at the coil you're using and see what kind of coil you have. I'm assuming you're using a 12 volt coil, but it's either a 12 volt coil that requires a ballast resistor or it is a non ballast coil that takes a straight volts.

The purpose of a ballast coil is to boost the output of the coil during cranking. Cranking pulls the battery down and therefore lowers the output of the coil. To compensate for this on cars and trucks, The ballast coil was introduced. The coil is wound so it gives full output at a lower input voltage. It's fed via the ballast resister which reduces the voltage into the coil which would end up being around 7 volts. During cranking, the ignition switch would short out the resistor to increase the input voltage to a full 12 volts and therefore the output of the coil for better starting.

Now, if you have a ballast coil and you run 12 volts to it continuously without a ballast resister to reduce the input voltage, the coil will over heat and eventually burn up.

How do I know this? I made the mistake myself and had to replace a coil as a result.
 
The electronic ignition units used on these tractors do not use the bypass system during starting. The excess voltage applied to the coil during cranking can overload the electronic unit according to the information I have gathered. So, we still need to know what coil he is using and some coils do not show on them if they require a resistor or not so therefore, get out the ohm meter and test it then you know.
 
87 Blue, you're on the right track, but to clarify a few loose ends let me add these comments to your post with all due respect:


1) "The purpose of a ballast coil is to boost the output of the coil during cranking."

That's indeed true in that it boosts the coil output while cranking, but its the coil in conjunction with THE BALLAST BY PASS SYSTEM that does the job.

The way I would explain it is: The purpose of an externally ballasted coil coupled with a BALLAST BY PASS (while cranking) SYSTEM, is so the ballast can be by passed while cranking (when battery voltage is reduced) so the entire unballasted battery voltage (be it 12 or reduced to 10 due to cranking voltage drop) is applied to the coil momentarily which increases spark energy to improve cold weather starting. If you have a 6 volt coil and an external voltage dropping (12 to 6) ballast resistor, what happens is while cranking you remove the ballast so the 6 volt coil sees the unballasted 12 down to 10 or so volts (NOTTTTTTT the normal 6) to increase spark energy. Without the ballast and by pass system that's not possible.

2) "Cranking pulls the battery down and therefore lowers the output of the coil. To compensate for this on cars and trucks, The ballast coil was introduced."

Id say to compensate a coil coupled with an external ballast resistor and a ballast by pass (while cranking) system was introduced.

3) "The coil is wound so it gives full output at a lower input voltage."

SORRY I CANT AGREE WITH THAT

The coil DOES NOT gives its full output at a LOWER input voltage, actually its output is less if voltage is reduced.

4) "It's fed via the ballast resister which reduces the voltage into the coil which would end up being around 7 volts. During cranking, the ignition switch would short out the resistor to increase the input voltage to a full 12 volts and therefore the output of the coil for better starting."

You got that part basically correct

Hope this helps clarify things a bit

Best wishes n God Bless

John T
 
I was buisy in a Manufacturing lab and was going to do what you have done. 20 students working on CNC mills , lathes, and welding was pulling my attention. Jim
 

Wife had a colonoscopy today and we just got back and missed the posts. Here are some data points.

a) The coil is a NAPA ic14sb and there is no external ballast resistor. I'm on the 3rd one.
b) with the engine running, the alternator is putting out 14.3 volts (measured with a Fluke 117 multi-meter). I'm on the second one.
c) With a cold coil and tractor not running the resistance across the coil is 3.4 ohm using the same fluke meter.
d) When the tractor cuts out I notice the amp meter is 2/3 of the way between zero and 'D'. Something seems to be pulling mucho amps at that time.

I need a path forward, this is driving me nuts. Will swapping out the electronic ignition provide any logical / conceivable benefit? New coils don't seem to help.
 
What does it say on the coil??? Most will in dead have writing on them saying something like no external resister needed or it will say resister needed. That is about the only way you are sure if you need a resister or not
 
Well, it appears that coil does not require a ballast resister according to NAPA. I pull this from their website.

PRT840101 Printed in U.S.A. Form No. -3/144/81
INSTALLATION INSTRUCTIONS
COILS FOR 12-VOLT SYSTEMS
RESISTOR NOT REQUIRED
1. DO NOT INSTALL these coils on 12-volt systems equipped with a resistor or
with resistance built into the wiring harness.
2. SELECT THE RIGHT COIL by referring to the application guide in the
Catalog.
3. COIL POLARITY MUST BE CORRECT. If the negative battery post is
grounded, the coil terminal marked (-) must be connected to the distributor. If
the positive post is grounded, connect the coil marked (+) to the distributor.
4. All connection must be clean and tight. Make sure the coil high tension wire is
firmly seated in the coil tower and the spark plug wires are firmly seated in the
distributor cap towers.
 
The picture on NAPA on line store clearly shows "use with External Resistor " in the image.
I would use a cheverole ballast resistor from a 1966 impala 6 cylinder. Jim
 

The NAPA catalog clearly states the ic14sb coil DOES NOT require an external resistor. That is also stamped on the coil itself. The ic10sb coil DOES require an external ballast resistor and that appears to be the picture they used on the NAPA website.
 
(quoted from post at 17:35:20 03/23/15) The picture on NAPA on line store clearly shows "use with External Resistor " in the image.
I would use a cheverole ballast resistor from a 1966 impala 6 cylinder. Jim

I think the picture is generic. That coil is NAPA lower cost option. The spec sheet for the Echlin version of the same number coil lists it as not using any external resistance.
 
I've used several IC14SB coils. Definitely direct 12 volt no resistor required.

I've assumed the napaonline picture is illustration only, not actual photo
 
If you have a "hold against" ammeter, use it to read current draw going to the coil---or going to the electronic ignition. If your ammeter is indeed reading around a 15 amp discharge when the ignition fails, that is excessive.
I would guess that the electronic ign. is putting
excessive voltage/ current to the coil.
Your alternator putting out over 14 volts is a bit high, but shouldn't affect the ignition that much.
Alt. should be on the order of 13.6 to 13.8 volts.
Guess I'd lean towards a defective electronic ign.
unit.
 
14.3V is perfectly fine. Actually a little low. An alternator normally puts out 14.8V.

Also alternators are notoriously hit-and-miss from the auto parts store. We went through three Delco 10SI rebuilts before we got a good one recently. They would run decently for a few minutes, then the voltage regulators would fail.

The coil you are using is not the coil you think it is. I suspect they are giving you mislabeled 6V coils. Try something other than a NAPA coil.
 
a) The coil is a NAPA ic14sb and there is no external ballast resistor. I'm on the 3rd one.

b) with the engine running, the alternator is putting out 14.3 volts (measured with a Fluke 117 multi-meter). I'm on the second one.

THAT VOLTAGE SEEMS FINE AND AROUND NORMAL

c) With a cold coil and tractor not running the resistance across the coil is 3.4 ohm using the same fluke meter.

SOUNDS LIKE ITS A 12 VOLT COIL IE NO BAllAST SHOULD BE NEEDED

d) When the tractor cuts out I notice the amp meter is 2/3 of the way between zero and 'D'. Something seems to be pulling mucho amps at that time.

COULD BE A SHORT SOMEWHERE OR A FAULTY VOLTAGE REGULATOR/ALTERNATOR IS DRAWING EXCESS CURRENT AND DROPPING BATTERY VOLTAGE SO LOW A WEAK SPARK MIGHT RESULT

Will swapping out the electronic ignition provide any logical / conceivable benefit?


I DONT THINK THE ELEC SWITCH IS THE PROBLEM BUT A SHORT SOMEWHERE CAUSING EXCESS CURRENT FLOW AND REDUCED VOLTAGE MAY BE????

Since it appears to be a 12 volt coil I cant explain why its overheating unless the switch is staying closed for such a long duty cycle that's overheating the coil SO PERHAPS THE SWITCH IS THE PROBLEM DESPITE MY THOUGHTS JUST ABOVE. If it stays closed a long time that could explain coil overheat and ignition failure.

BEST GUESSES
1) Alternator or Voltage Regulator is faulty causing a short reducing coil voltage causing weak spark

2) BUT if the coil is overheating and its a 12 volt coil and the Voltage Regulator and Alternator are all okay PERHAPS THE SWITCH IS FAILING AND REMAINING CLOSED WHICH WOULD OVERHEAT THE COIL PLUS CAUSE NO FIRING

John T
 

I will crank it tomorrow and let it run in neutral and measure the alternator voltage and coil resistance every 10 minutes. What I don't get is: if the alt volt regulator is failing high, why would the amp meter go almost full discharge? And yes, this my second 10 SI alternator. Thanks for your feedback!
 

The elec ignition is about the only thing I haven't changed. Is it possible for it to cause the coil to heat up after running awhile? I am considering replacing it, but they are about $90. Thanks for your comments.
 

Thanks John T. I'm confused however. With the switch in the run position there is 12V to the input of the coil. The start position puts 12V to the starter solenoid and the switch then releases to the run position after cranking. If the switch were sticking, wouldn't the starter continue to spin? I'm trying to understand how the starter switch could cause this problem. If I turn the switch to the run position and the coil input reads 12V, isn't that normal? With the switch off, the coil input reads Zero V.
 
I meant the ignitions elec switch (NOT starter) may be hanging closed longer then normal which could account for a warm coil plus ignition failure

John T
 
It means the elec switch closes to conduct coil current (like when points were closed) but then opens (when piston is at TDC and points were open on high cam lobe) to fire the plug. HOWEVER perhaps the elec switch is bad and its staying closed which would make the coil run hot plus kill the spark.

THATS A LONG SHOT (1 of the 2 possible causes I guessed at above) BUT GRASPING AT STRAWS NOT BEING THERE TO SEE WHATS HAPPENING

John T
 
What does the maintenance manual or IT manual say.

Find an old 1948-1950 Motors Manual and it will describe the basic operations of the old ignition and uses for resisters, coils and wiring.

Thanks to my Dad, Gus!
 
Is the alt. a 1 wire or does it have the "sense" wire going back to the battery?
My brother put a 1 wire on his pickup--72 amp. He has been jumping his backhoe with a bad battery, & it is only putting out around 15 amps while jumping.
An alt should charge nearly 2/3 rated amps in this situation. All power to people who get along with the 1-wire units, but from what I've seen, they leave a lot to be desired.
 
A wire that grounds out as the tractor heats up causing the voltage to go low would cause the ignition to fail, but not the coil to get hot. Excess dwell (time "on" would do it however. A failure in the module could cause that. Jim
 

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