coil question and introduction

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charleswise

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Apr 21, 2021
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coldspring, TX
Hi guys, new to this site. I bought an old International Cub Cadet 122 lawn tractor. It was running good and then when I went to start it, it would not start. It made a sound like the starter was out. I accidently left the key in the 'on' position and as I was looking it over the coil started to hiss and pop and then it exploded. Never had that happen before. I bought a new coil but on closer inspection, when the key is on (the old coil is still on) it's still doing the same thing. I'm hesitant to put the new coil on because I don't want a repeat of the same event. The wires are not grounding out. The battery is new. I followed one of the leads to what appears to be some sort of relay switch; don't know if that might be out and causing the problems. Does anybody have any ideas before I tear into this thing? Thanks
 
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Charles,I've never seen an "exploded coil"Doesn't mean it can't happen.Most electrical issues can be traced to a short somewhere.Did you unhook the wires from coil and turn key on again to observe. I don't understand your terms"sounds like starter going out" Try explaining that differently .....You said the coil exploded and then you said it's still hissing and popping???? We are thinking that an explosion is like a grenade going off ..can you explain better??
 

charleswise

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coldspring, TX
So yes it was like a grenade going off. I can take a picture in the morning if it helps, but the top of the coil blew off. It's like a can lid, separated from the bottom. I've tinkered with mechanics my whole life and never saw the like. When you turn the key you don't get the regular cranking noise, it's more like a whirring noise. And when the key is on, the power is going to what's left of the coil. It's getting hot and I guess there's some kind of oil or lubricant inside the coil because you can hear it getting hot and popping. I've started looking for shorts, tracking down wires; like I said I ran one of the coil wires (there's two on this one) to a switch of some kind. The other wire runs into a harness and into the tractor's firewall or what passes as one. I haven't gotten in there yet.
 

charleswise

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coldspring, TX
I was heading back in the direction of that train of thought. Unless anyone has any other ideas, I'm going to hook up the new coil and see what happens.
 

kashaver

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Kelvin Shaver
The coils (The old ones at least) were filled with an oil. Probably a PCB type of oil. The oil helped conduct the heat from the windings to the canister or case the coil is in so it can cool.

I had a coil 'pop' years ago on a tractor. I had shut the fuel off and was letting the engine run completely out of fuel and forgot to go back and turn the switch off when the engine quit running. About 10 minutes later it 'pop'ed. Oily smoke everywhere. Cracked the cap on the coil.

To answer what I think is your question, when the ignition switch is 'on' there is constant power to the + side of the coil. If the engine is not running and the ignition points are closed and the ignition switch is on, there is a completed circuit through the coil to the points and that is how the coil overheats. It is the points opening that circuit that causes the secondary windings in the coil to make a spark. Its also the points opening on a regular basis when the engine is running that keeps the coil cool enough to function without over heating.

So you don;t want to leave the ignition switch on without the engine running for long periods of time.
 

lhinds

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Luther Ray Hinds
With points closed the coil is shorted to ground. If ignition switch is on and points closed they weld closed and can cause the problem you have.
 

kmcconaughey

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What David is referring to is that the correct coil has to have the resistor inside it. Here's some that would be correct: EDIT: Please see David Kirk's post below regarding coils.

Coils_01.JPG


Coils_02.JPG


The coils shown above are some that CC Specialties has.

David Kirk (Kirk Engines, Inc.) also sells a Bosch coil that works. I have one of these on one of my Cub Cadets.

EDIT: I have a second Bosch coil on a Kohler, K241, that is not yet in a Cub Cadet.

Kirk Engines
 

Beltrack

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Ditto the above. I left the key and an old (1969) Triumph motorcycle. I was camping out in Kansas at the time. I had just refueled and the fuel tank had a slight leak when topped off. Well the fuel dripped onto one of the two coils which was red hot because the key was left on. This caused a hissing sound as each drop hit the coil. I initially thought it was a rattlesnake and was scared to move. When I finally screwed up my courage and approached the source of the noise, I discovered what was going on. I switched off the key and got way away from that potential napalm bomb until the hissing ceased. The next morning I started her up and she was running on one cylinder (it was a twin cylinder with two coils). I limped down the road at 30 mph to a dealer in St. Joseph, Missouri for a new coil. No other damage accrued from my screwup.
 

tkhoffman

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Tony Hoffman
Right off, if coil exploded, don't put voltage to it, it's been compromised. I have had old cars with key left on, weld the points together. Usually it just ran down the battery. Whirring at starter. Maybe low battery not letting Bendix gear to shoot up to the engine flywheel.
#1 check for full battery charge.
#2 disconnect coil then see if Starter is happy again
#3 look at points for damage.
#4 get new coil and put it all together and see how it goes
 

dkirk

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My rule of thumb - if the Kohler is not running, the key is in my pocket.

Don't retrofit with a hotrod, high energy coil. Primary resistance should always be no lower than 3.0 ohms. Lower resistance draws more current. The hotrod coils are wound for 1.2 ohms primary resistance which means they draw high current causing the points to burn very quickly.

Now for my controversial comment for the day - ignition coils are NOT fitted with internal resistors as is widely thought. Its all about the length of wire, or turns, used in the primary winding. Fewer turns on the primary means lower resistance resulting in higher turns ratio, thus higher secondary voltage. More turns on primary means higher resistance, lower turns ratio, thus lower secondary voltage. The difference in secondary voltage has no effect on running or starting on these single-cylinder engines. Logically, there's no reason to put a resistor in a coil - heat generated would be detrimental. A ballast resistor is a different story - that's externally mounted for cooling and is normally used when a 6V coil is used in a 12V system. If you don't believe me, cut an old coil open and if you find a resistor, let me know and I'll admit I'm wrong.
 

Greg Riutzel

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I accidently left the key in the 'on' position and as I was looking it over

That's the mistake. I've done the same but not on my Cub. In fact, it states in the OEM Kohler manual that coils will do exactly as you witnessed with key on and the engine not running. What it doesn't say is how long it takes, but I figure anything over 3-5 minutes depending on the battery state. Be careful to get the correct coil as posted. Single cylinder engines have long dwell time and the incorrect primary resistance, or too low a resistance, with shorten point life.

Now for my controversial comment

Thank you too! My old Delco books mention high vs low resistance coils. Somehow over time resistance has morphed into resistor.
 
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mgwin

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Marty A. Gwin
"Well I'll be a monkey's uncle!" (another phrase I have heard all my life)
Learn something new all the time.

Speaking of learning something new, anyone know how to check a condenser? I thought I had that info somewhere, but since I am a senior (somewhat), I can't find it.
Can a condenser go bad gradually? or is it like a light bulb, when it goes, it goes.
Can you help us out on this David?
 

mgwin

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Found out something else I already knew. LOL! You can google this stuff on the internet. Imagine that! Darn migraines are messing with my head.
One thing though, you can't believe everything you read/see on the web though. Helps to check several sources, unless you were to ask Charlie! :errrr:
The condenser is a version of a capacitor.
I have read it can go bad gradually, or all at once. Would like some input on that statement.
 
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