Coils keep cracking?

erikyater

New User
Working with a Ferguson TO20 that was converted to 12v neg ground system. It has an alternator, 12v coil and seems to be wired correctly according to a diagram for 12v systems. This tractor ran fine for a year or so, but this year, it wouldnt fire right up. After rebuilding the carb, checking fuel flow and spark, still would not run, just backfires and pops. Then at the end of the day, I somehow noticed a crack in the top of the coil, which I knew had to be the problem. After replacing it with another 12v coil, and rechecking wiring, we got about 3 hours on it running really well, then it did the same thing to a brand new coil. Could the alternators regulator be bad and letting too much into the primary, or possibly just overheating although the engine does not overheat. I tried getting it to fire back up tonight after the failure to check the output from the alt, but couldnt get it running long enough to do so.
 
Check the coil polarity is correct - negative side to distributor points: positive side to ignition.

Change the condenser in the distributor.

Are you using the correct 12 volt coil? (Not a coil designed to operate with a resistance?)
 

Neither coil polarity nor a bad condenser should cause a coil to fail

(Bad condenser will just cause weak or no spark)

I'd check your charging voltage, but if the running voltage is high enough to damage the coil, it would probably be boiling acid out of the battery like mad

This sounds to me like improper coil and or resistor

You don't go around (by chance) leaving the ign on with the engine not running do ya?
 
This sounds like a bad ignition switch or bad key switch. It sounds like for some reason the ignition is getting power after the engine is off. When the engine is off and if the points are shut and the ignition gets power it will blow the top of the coil off or split it.
 
Thanks for replies. Polarity is correct on the coil. 440roadrunner, i agree and thought the same if it was juicing the coil too much why hasnt the battery done the same, unless its just enough for the coil, and not enough for the battery. Im pretty sure there is no resistor, but shouldnt need one for a true 12v coil right? The coil i stuck on it was from Tractor Supply(closest store) and marked for IH and said 12v, nothing about its resistance. The first coil that we ran with for almost two years had no markings either, but worked all that time. As for the ignition switch being bad, it shuts down when the key is turned off, but maybe something to look at. Thanks.
 
A high primary current usually causes an internal failure in the insulation that causes the primary winding to short out. Make sure that your high tensionsocket is lean that the lead istotally in the socket tightly, and the boot is clean and snug over the coil tower. This is a new one on me.
 
Today, I actually took a day off work to try and figure this out. I stopped at Napa, got the 12 volt coil that is stamped "For use without external resistor", so that problem is solved. It fired right up. So I checked the voltage at the battery to check the alternator, and it is driving my meter crazy flashing up over 1000 volts, so I quickly disconnected and shut her down in fear of cracking another coil and damaging the meter. I disconnected the alternator wires, started and ran off the battery, and still had wild readings. So thinking the alt could be somehow shorted throwing voltage on the ground, I completely loosened and took the belt off. I know some of you may worry I ran it like that for long, but I didnt even run it for 10 seconds, so I think Im okay without water pump for that long, but STILL had crazy readings at the battery. Decided to throw a meter on the condensor, it wasnt reading what it should, and the points i put in worked, but not quite right. So I headed back to TSC and they must have just got in an ignition tune up set for the to-20. Changed both condensor and points and rotor button. Same thing. Runs perfect, but I get crazy high voltage on either side of the coil, whether its at the dist connection or the keyswitch. I checked for shorting between the dist. body and points connection and it checked out except of course when points are closed. New dist. cap does same thing. I cant find copper plug and coil wires, but tried others I had from the parts cabinet, no change, and the dust cap under the rotor button I tried from the old fergie thats been sleeping for a few years and nothing changed. I know this is a long post but so is the grass. Any ideas you got Id love to hear. Thanks.
 
Find an analogue meter toss that digital one that can't stand ignition noise in the area. Without a meter that works in that environment you can't tell a thing.

Check the coil case temperature after half and hour or more of running. It shouldn't be hot.

Gerald J.
 
get a old fashioned analog meter and try using that. auto parts store should still have those cheap. yes it is tough living with with all this digital stuff. you just cannot eliminate analog testers and controls. thats what i like about my two fergusons no digital nothing on them. i know they do not like that digital stuff. i tried installing a electronic horn on the te20 that plays a bunch of songs thru a p.a. speaker. worked great till i had it running.
 
Thanks again guys, cant believe I overlooked that one, guess only thing on my mind was getting her going. Im only 28, Ive loved any kind of engine from steam to combustion since I was little, and I do have an analog in my own box at home. I fix computers on the side and fix video entertainment equipment as a steady job, should have thought of this. Ill post again tomorrow night possibly. Thats hilarious about the horn John.
 
Checked on it today with the analog, things check out ok. Im going to brushog with it and check temps and voltages as I run. Ill post to close the case. Thanks.
 
Finished cutting the property, ran about 2 hours, checked volts and temps, everything seems good, coil was about 120 degrees F, checked a few times could even keep my hand on it. Hope it stays this way. Thanks.
 
Jerry, if youre reading this, we finished last season just fine. Put it away in the garage under cover for the first time in a while I think. The battery was old and wouldnt take take a charge, threw in a new one, checked fluids, cleaned sediment bowl and added some fresh fuel. Before parking it last year I added some fuel stabilizer. Fired right up in one shot. But out of curiosity for the alternator output, I pulled the ground off of the battery and it shut down. Yeah, this year were checking everything first before getting stuck in the field. Turns out the idiot light bulb in the circuit was corroded at the base and not making contact. Cut for about 30 minutes and did just fine. To end this story, I now have to get a replacement rear caster wheel for the JD 272 finishing mower. As I was backing into the garage, the wheel got caught sideways and snapped the spindle, I dont know what I would do without the excitement except get things done.
 

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