1972 IH 140 coil UPDATE w/Data


I posted yesterday about a problem with coils that seem to keep burning up on my '72 140. After 30 or 40 min the tractor just cuts off while mowing (normally at the furthest point from the barn) and the coil is red hot (even with a new coil). After sitting for about 20 or 30 minutes the coil cools off and it cranks back up and runs for awhile then repeats. This makes me suspect the coil but it may be coincidence. I have put new coils on 3 times chasing this problem and replaced the alternator to no avail. (

The alternator (2nd one, it's been on 6 mos)is a 10SI 12V neg ground and the coil is a ic14sb from NAPA. Tractor has an electronic ignition purchased from this site.

Today I cranked it up, set at mowing rpm's, and read voltages with a Fluke 177 multi-meter every 5 or 10 min. I measured voltage from Alt output to frame, and from coil output to frame. I also cupped my hand around the coil to get an idea of how hot it got.

The Alternator put out a steady 14.6 volts for 90 minutes. The coil (3.4 ohms cold resistance)output started at 10.1 volts when first cranked and cold. At 20 min the coil output had risen to 11.4 volts and had warmed but I could keep my hand on it.

The coil output stayed at 11.3 volts and it had warmed up at 40 min such that I could only cup it in the palm of my hand for 5 sec.

At 60 min I heard sputtering and the coil voltage was gyrating between 9.5 & 11.3 V. It smoothed out eventually and didn't repeat. Could the electronic ignition cause this?

At 80 min, coil voltage was 11.1, and I could only hold it for 3 sec.

I then mowed for 10 min and at 90 min coil voltage was 11.2 and I could barely hold it for 3 sec. I then shut down.

For some reason it didn't cut off like it normally does after 30 or 40 min.

The alternator and internal voltage regulator appear to be OK. I'm not sure about the coil and elec ignition. Is this coil output voltage normal. It seems the coil heated to over 140 deg F, but when it cuts while mowing it's much hotter. I need to change something, but just not sure what. Is there a better coil I can buy than ic14sb? Should I swap the elec ignition?
 
im not a big fan of the aftermarket electronic conversions. seems they either work great or make you pull your hair out. if you have the old breaker point set up, i would try switching back to that and see what happens. if the coil settles down and acts normal, you found the problem.
 
A couple comments:

1 - Your voltage readings indicate the alternator is performing within specs. No problem there.

2 - Your coil is running WAY too hot. (It should run only slightly warmer than the ambient air around it.) And a hot coil means it's drawing way over design current. My guess is it's a "6 volt" coil and which is being supplied nearly double the design voltage. (BTW doubling the voltage QUADRUPLES the heat generated inside the coil).

I'm not familiar with your electronic ignition. It sounds however your coil is mismatched to the ignition. Or perhaps it needs an external ballast resistor to work with the coil.
 
I'm with you Glennster!

I own several Farmall, Oliver and M-M tractors all with the OEM (breaker point) ignition. Everyone one of them runs great. And none has given me a lick of ignition trouble.......ever!
 
Excess dwell (time "on") would do it however. If the dwell on the original points is 35 degrees, then in 360 degrees it has the coil on for 120 degrees out of 360. That is much less than 50% of the total time. If the electronic module is allowing the coil to be on 200 degrees of rotation out of 360, the coil is "ON" almost twice as long. If the coil duty cycle is normally on for less than 50% being on longer will overheat it dramatically. A failure in the module could cause that. Jim
 
With the ohm reading you are getting on the primary of the coil it should not need a ballast resistor. I think the idea of excess dwell time has merits. I would be trying to run a test to see just how many degrees that unit is turned on. Or, just put the points back in and run it for a while to see how the coil reacts then. As far as the apparent high discharge reading on the ammeter when the problem showed up, I would just leave the switch on when it dies and quickly disconnect the feed wire to the coil to determine for sure if the coil was drawing the current or some other circuit.
 
Hey Gator,

Could it be
that the electronic ignition is defective in such a way that the dwell time (old timey phrase) has increased so much that the coil is drawing current almost 100% of the time and not getting a chance to cool down. Old time dwell meter or an ignition scope might yield some useful info. Just a thought.
 
Two ideas:

1. Try the Pertronix coil designed to work with the electronic ignition.
2. Try a ballast resistor, even if it doesn't call for one.

The installation instructions for the Pertronix electronic ignitions are VERY specific about the primary resistance of the coil
 
Doing a little math here, if the feed from ign switch is 12.6 from a full charge battery and primary resistance is 3.4 ohms the current draw through coil should be 3.7 amps. When running with full charging voltage of 14.6 the current draw should be 4.29 amps provided primary resistance remained the same. Doesn't seem like too high a current draw to heat the coil unless like previously stated, dwell is too great. Unfortunately, not much you can do about dwell except changing to a different electronic unit. A standard ballast resistor would, in my opinion, increase resistance too much causing weak spark, but if I had one laying around I would sure try it just to see what happens. Easy enough to check to see if you have good hot spark with resistor added and running it to see if coil gets hot and engine performs. One thing for sure, I would not just put on another identical coil.
 
The output side of the coil should be either the same as input voltage or zero. The reading you get is an average of the two conditions.

What you are seeing would be bad if using a points distributor but with an electronic set up the readings may be normal. Contact points need time to physically move but the electronic system only needs to open the circuit went a spark is needed.
 
Bob, I concur about the functioning of the alternator.
However, should one still be worried about the charging system and its potential effect on the ignition system, why not removing the alternator belt for a while and see what happens?
(Assuming the 140 is "belted" similar to a Super A, with a separate generator/alternator belt driven off the fan hub.)
 

Thanks for all the insightful responses. Excess dwell sounds reasonable. This site says their Elec Ign Module won't work with solid plug wires. I checked and mine are stranded.

I'm going to NAPA and get a ECH IC14 coil ($36)and new mounting bracket. What are the chances the current coil has been damaged?

Before installing I will inspect the elec ign mod and see if I can see anything loose or frayed.

If the coil gets hot again I'll swap the EIM. I'd rather spend $90 for an EIM than revert back to points and condensers.
Maybe I should just swap the EIM first.
 

I cannot duplicate your math here. With 35 deg of dwell, and the Elec Ig Module fires 4 times per revolution, 35 deg x 4 per rev = 140.

140 / 360 = 39% of the time. What am I missing?
 
yup and the best thing you can keep a complete tune up kit on the tool box in the tractor. if you have a problem in the field, you can change out everything and get back to work in 20 minutes or so, all for about 50 dollars. saves a walk back to the barn.
 

Would high resistance in the plugs and plug wires contribute to heating the coil?
I notice the elongated nuts on top of the plugs work loose. I tighten them but they still work loose.
That might increase resistance in the coil output. How do the rest of you keep those fitting tight?
 
"I checked and mine are stranded."

What have you got... spark plug wires with a dozen or so individual copper strands would be considered "solid" wires.

What you are looking for is RESISTANCE/suppression wires with a carbon and fabric core OR a fine metal strand wound in a continuous coil over a carbon core.

I'm gonna GUESS you have "solid" wires, which Pertronix cautions against.

That being said, I don't think it has ever been explained EXACTLY why Pertronix doesn't want "solid" wires used, and (if you do actually have "solid" wires) I wouldn't bet that is what's causing the coil heating you are experiencing.
 
I too have lost coils on the electronic ignition. I call the company and they said that I have a match coil to the unit that I am using. Order coil no more problems. Hope this helps
 
I know the dwell is not exactly 35. I know the numbers I was using were not (as a result) accurate, but the idea is that a coil is on less than 50% of the time (an explanation, not math) that lets the coil cool between firings. Remember the advise to never leave the Key on in the car because it will ruin things. That is the reason, the coil builds up heat and fails. Jim
 
Not the issue. Stranded wires (there are no sold wires, only non suppression wires made from real wire from end to end in strands with a slight twist) The use of suppression wires in this case is because with the recommended plug gap, the voltage is higher and produces much more radio static. Neighbors begin to complain and it started when you put on the electronic ignition. The company doesn't need the bad publicity. The use of Magnetic suppression wires (a bit expensive) provide no resistance and no radio noise. They are also less prone to structural failure. They would be found in a Kit for maybe a Datsun B210 or other 4 cylinder car. Jim
 

"non suppression wires made from real wire from end to end in strands with a slight twist"

Thanks Bob and Jani. That's exactly what I have. Looks like I've got solid core ignition wires.
The resistance from the 1 foot long wire from the coil to the distributor input is 0.4 ohms.

Do I need to change these wires? What should I get and from where? As Bob said, this may not fix my hot coil problem.
Other than radio interference, is there any other benefit?
 

I have used their flame thrower coils and they got red hot as well.
So if a coil gets red hot, is it trashed and needs to be replaced?
This one takes about 60 min to get real hot after it cools down (like over night).
 

I understand there are 2 time periods in a coil:

First is when current flows through the primary windings and builds up the magnetic field.
The second is when current stops flowing through the primary windings, the magnetic field collapses, and current is generated in the secondary windings.

When you say when the coil is "on", are you referring to the first time period above?

Does "dwell" refer to the first or second time period?
 
The circuit breaking action (electronic or points) initiates the spark and the spark jumps the gap in the plug several times as the coil magnetic field collapses. Duration probably a millisecond. The coil primary is now not connected to the 12v system and is "off" until the points close again. This "off" time produces no substantive heat and does not contribute to that issue. The only time period that there is thermal buildup is the duration of the closed points/or conducting transistor to ground (electronic) Jim
 

I'm beginning to understand. Found this: "The period of points closure is typically expressed as degrees of distributor rotation. In a four cylinder engine, the angle between each ignition cam lobe is 90° and the period of points closure or "DWELL" is usually a bit over 45° of distributor rotation."

So you're saying coil heating occurs when the points close (ON). Looks like that's about half the time. When the points close, does the current flow through the coil to ground?
 
If there is just one belt driving fan, water pump and alternator you should not remove that belt for longer than say 5 minutes running time, lest the engine will boil and overheat.
Note: on a Super A the fan is driven by a belt from the crankshaft pulley. The generator is driven by a second belt from a second pulley on the fan hub. (No water pump on Super A.) So, the second belt can be removed to disable the charging system, while retaining the cooling.
 
Yes. the system is supplied voltage from the ignition button and the current flows through the coil to ground through the electronics (or points) to ground. Jim
 
I don't have a number, but the "Ignitor" has LOTS of dwell, I'm gonna speculate MORE than a properly set breaker points. Outside of a VERY short period of time when the spark is occuring the electronic switch is "closed", and the coil is heating.

That's why when you leave the ignition switch "ON" with a Pertronix Ignitor, it is VERY likely it will be in "ON" mode, trying to overheat itself and the coil, and killing the battery. The only way it shuts down is if the engine has stopped EXACTLY at a firing point of one of the cylinders.

On the other hand, the Pertronix II and III units (not available for all applications) control dwell to lessen coil heating during operation and allow the use of lower impedance ("hotter") coils, and shut off coil current if the engine is not rotating. You can read about the dwell control features of the II and III on Pertronix's website.

Gator, what I would suggest is to install a low value ballast resistor and see if coil heating is less, yet spark is still "hot" enough for the engine to run properly.
 
That sure sets the stage for changing the coil to one with more resistance, or adding a one Ohm resistor to the coil Checking the value of several ballast resistors (on the shelf) might be reasonable. Or using the coil recommended by Pertronix. Jim
 
I may get chewed out here, but my understanding of the electronic
ignition systems is that they only send coil voltage when the
"magnet"--on the rotor passes the pickup unit sensor.
At this point, the pulse fires the SCR delivering voltage to the
coil.

I was unaware that the coil had voltage applied to it during "dwell
time". Could be wrong.
Jim
 

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