AC D17 Coil overheating

AcHelp12

New User
Very amateur mechanic here. I have been helping a family member with his D17. The tractor runs great, but eventually will start sputtering and backfiring and shutoff. After it cools down for awhile it will fire right back up and run great until it happens again. He thought the issue was the coil overheating, that was replaced and fixed the problem temporarily but the tractor started doing the same thing after a while with the new coil. In addition to the coil failing, the ignition key will not turn the tractor off, he needs to disconnect the wires to the ignition. I would like to think that the faulty ignition switch is causing the issues with the coil, but do not know enough to say that confidently. Any advice?
 
If it has an alternator on it for a charging system the wiring is likely to have been done incorrectly
 

If the ignition switch is the type that feeds 12 volts to the coil on "start" and only 6 volts on "run", it could potentially be a problem with the switch.
I'm guessing feeding the coil 12 volts continually might cause it to overheat.
 
Is the D17 a 4 cylinder or 6? If it is a 6,make sure your coil is for a 6 cylinder. if not it will give too much resistance. What kind of alternator do you have? If you have a 3 wire alternator make sure you have a diode or LED wired into the lead from the alternator to the ignition switch. If it doesn't have an LED or diode that will cause run on after the key is turned off. Been through similar with my D19.
 
(quoted from post at 11:03:46 07/27/20) Is the D17 a 4 cylinder or 6? If it is a 6,make sure your coil is for a 6 cylinder. if not it will give too much resistance. What kind of alternator do you have? If you have a 3 wire alternator make sure you have a diode or LED wired into the lead from the alternator to the ignition switch. If it doesn't have an LED or diode that will cause run on after the key is turned off. Been through similar with my D19.

D17 only had a 4 cylinder gasoline engine or a 6 cylinder diesel. Your D19 was 6 cylinder for both gas and turbo diesel.
 
(quoted from post at 12:03:46 07/27/20) Is the D17 a 4 cylinder or 6? If it is a 6,make sure your coil is for a 6 cylinder. if not it will give too much resistance. What kind of alternator do you have? If you have a 3 wire alternator make sure you have a diode or LED wired into the lead from the alternator to the ignition switch. If it doesn't have an LED or diode that will cause run on after the key is turned off. Been through similar with my D19.

The parts books show the same coils being used in the D17s and D19s. I really think the coils don't care about number of cylinders, they do care about voltage. A coil needs to have internal resistance for the primary voltage of the system, or be used with an appropriate external resistor, to limit current going to the points.

Bypassing the resistor for higher voltage to the coil during starting is normally done through the starter solenoid, not the switch, in systems I'm familiar with.
 
1 cylinder or 2 or 3 r 4 or 5 or 6 or 8 ALL use the same coil. Coils do not care about how many cylinders and engine has a coil cars about how much voltage it has going to it and a 6 volt coil will over heat if used with 12 volts unless there is a correct ballast resister in line
 
Talk to the gentleman at B and B custom circuits. He explained that there is a difference in the internal resistor in a coil for a 4 and 6 cylinder engine. I bought a coil that was 12 volt internally resisted for my D19 and it was too much resistance for it and made it hard to start and it ran rough. Changed back to my 6 volt coil with ballast resistor and haven't had trouble since. Just didn't know whether his D17 was 4 or 6 and passing on what was told to me.
 
#1 no coil any more has an internal resister.
#2 a 6 volt coil will ohm out around 2 ohms and a 12 volt about 4 ohms. I have a coil on my Ford 841S that came off a Chevy pickup that had a 6 cylinder. But if you run the part number for a Chevy be it 4, 6, or V-8 the coils are all the same for say a 1965 Chevy. Newer one use a different coil set up. And yes I have used the same coil on 1,2,3,4,6 and 8 cylinder engines and NEVER had any problems
 
(quoted from post at 09:03:46 07/27/20) Is the D17 a 4 cylinder or 6? If it is a 6,make sure your coil is for a 6 cylinder. if not it will give too much resistance. What kind of alternator do you have? If you have a 3 wire alternator make sure you have a diode or LED wired into the lead from the alternator to the ignition switch. If it doesn't have an LED or diode that will cause run on after the key is turned off. Been through similar with my D19.

I will look into the alternator thank you. I am confident we have the correct coil in place.
 
The system I am most "familiar with" (Ford) does, in most cases use the solenoid to feed 12 volts to the coil during "start".
However, not all systems work that way.
I went out and looked at my D-17 Ser II and there is only one terminal on the solenoid other than the heavy duty ones.
When I looked at the diagram of the ignition switch in the parts manual, it appears it has both S and I terminals which leads me to believe that, in this case, the ign sw is the controller of voltage to the coil in both start and run modes.
It appears that some D-17s use a separate push button starter switch. Not sure how the process works there.
I have no idea whether or not the ign sw is causing the coil to overheat; I just threw it out there as a potential reason.
 
(quoted from post at 08:20:29 07/28/20)
The system I am most "familiar with" (Ford) does, in most cases use the solenoid to feed 12 volts to the coil during "start".
However, not all systems work that way.
I went out and looked at my D-17 Ser II and there is only one terminal on the solenoid other than the heavy duty ones.
When I looked at the diagram of the ignition switch in the parts manual, it appears it has both S and I terminals which leads me to believe that, in this case, the ign sw is the controller of voltage to the coil in both start and run modes.
It appears that some D-17s use a separate push button starter switch. Not sure how the process works there.
I have no idea whether or not the ign sw is causing the coil to overheat; I just threw it out there as a potential reason.

"ignition switch has both S and I terminals"

"S" sends power to starter solenoid during cranking, "I" powers the ignition system during cranking AND normal operation, no provision for a starting bypass there, another terminal sending poser to the coil side of the ballast resistor would be needed.

What you may be overlooking is this... there are two types of ignition ballast resistors, a basic type that has a fairly constant resistance as it warms up, typically used with a "starting bypass" circuit", and the "PTC" (positive temperature coefficient) type. The "PTC" ballast resistors are commonly used in ignition circuits WITHOUT a "starting bypass". When the ignition is first switched "ON" the resistor has a low resistance for good spark during cranking, then it's resistance increases as it heats from current flowing through it to a safe operating level.
 
There are definitely ignition systems that use the ignition switch to by-pass the resistor to provide direct voltage to the coil during starting. I am not a mechanic but I've been around a few years......the new stuff confounds me but I have a little knowledge of the old stuff.
I know, I know....a "little" knowledge can be dangerous. LOL

Here is an example:
mvphoto59296.jpg


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"S" sends power to starter solenoid during cranking, "I" powers the ignition system during cranking AND normal operation, no provision for a starting bypass there, another terminal sending poser to the coil side of the ballast resistor would be needed.

What you may be overlooking is this... there are two types of ignition ballast resistors, a basic type that has a fairly constant resistance as it warms up, typically used with a "starting bypass" circuit", and the "PTC" (positive temperature coefficient) type. The "PTC" ballast resistors are commonly used in ignition circuits WITHOUT a "starting bypass". When the ignition is first switched "ON" the resistor has a low resistance for good spark during cranking, then it's resistance increases as it heats from current flowing through it to a safe operating level.
 
Well, you may have the answer right there.......however, I don't see any reference to a resistor at all in the diagram from the "Operator's Manual"
mvphoto59301.jpg

I went out and looked at my D-17 (Series II) again and I can't find a resistor....if there is one, it must be well hidden.
I didn't even find a thick pink wire like used by Ford for their resistor.
Maybe its built into the coil?
I sure hope a seasoned A-C mechanic chimes in soon to explain all this.
__________________________________

the "PTC" (positive temperature coefficient) type. The "PTC" ballast resistors are commonly used in ignition circuits WITHOUT a "starting bypass". When the ignition is first switched "ON" the resistor has a low resistance for good spark during cranking, then it's resistance increases as it heats from current flowing through it to a safe operating level.
/quote]
 
The D17 parts books make no reference to a resistor, or resistor wire, that I can see. Not all systems that had resistors used a bypass, they just went through the resistor all the time. Some Ford type solenoids had a bypass terminal, some didn't. Some Delco starter mounted solenoids had bypass terminals some didn't, Likewise for other brands. The intent of the bypass within the solenoids was that it only be activated during cranking. My thought is the original coil for the D17 was built correct for the voltage without the need for an external resistor. If a coil it built with the proper resistance in it, it doesn't get a bypass.

Brian,
I agree that things can be wired many ways, to the point it can be hard to say anything is 100% one way.

However, the first drawing you posted showing the ignition switch having one wire to the resistor ("I" terminal I believe you called it) and the wire being used to bypass the resistor from the what you called the "S" terminal (as I understood you); omits a circuit to the starter from the switch. I have to wonder how that was handled. Yes, a separate starter button could be used to engage the starter. However if a wire was run to the starter solenoid from the "S" terminal of the ignition switch in that drawing, the solenoid would receive a back feed whenever the switch is in the run position. The voltage/current loss in a back feed to the solenoid could cause problems in both the start and ignition circuits.

Just some thoughts, for what they are worth.
 
(quoted from post at 09:03:46 07/27/20) Is the D17 a 4 cylinder or 6? If it is a 6,make sure your coil is for a 6 cylinder. if not it will give too much resistance. What kind of alternator do you have? If you have a 3 wire alternator make sure you have a diode or LED wired into the lead from the alternator to the ignition switch. If it doesn't have an LED or diode that will cause run on after the key is turned off. Been through similar with my D19.

Do you have any resources on how to add a led? We are both newbies and electrical systems are not our strong suit. When the tractor sputters it will sputter cyclically. It will sound great for a few seconds, then sputter for a bit, then back to sounding normal. Could this be another cause? Or is it unrelated?

Thanks you everyone for the input
 
It depends on which alternator you have as far as wiring in the LED but this video really helped me when I was learning https://www.youtube.com/watch?v=5l2qro7PLIY
 
Also, are you absolutely sure it's electrical? Have you checked the Carb? It most likely is the electrical but it might not hurt to check just to be sure.
 

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