Magneto coil

[David 2344]

I have a lawn tractor model 44N877 that is shorting out the magneto coil. New coils willh work for about 10 - 30 minuets and then the engine dies with no spark. What are the possible causes for the coil to short out?

 

[bertsmobile1]

Take the kill wire off
Problem goes away = bad wiring or safety switch
Get a wiring diagram and work you way through it by using a snort jumper wire to bypass the switches one at a time .
Note the seat switch can not be bypassed and the switch must be fully plugged in as it has an anti tampering device in socket .

 

[ILENGINE]

I would be removing the kill wire from the ignition module and then testing for a 12 volt feed through the kill wire. that picture of the module looks like it has been cooked.

 

[David 2344]

I would be removing the kill wire from the ignition module and then testing for a 12 volt feed through the kill wire. that picture of the module looks like it has been cooked.

The damage is from high current flow through the coil. I am waiting for new coils to try again. Last try without ground wire coils burned out in 5 minutes! Would the air gap also determine the amount of current through the coil? The air gap has been set at .012". I was thinking that a larger gap might reduce the current flow.

 

[Scrubcadet10]

air gap will not effect the amount of current. Or enough to physically burn up the coil.

 

[bertsmobile1]

Gap effects the duration of the coil saturation and the peak voltage .
magnet strength determines the amps generated.
Neither of which are likely to have blown the coil like that .
Frankly it has me stumped so hopefully some one who knows more than I will come to the rescue.

 

[ILENGINE]

If that happened with the kill wires disconnected my next thought would be looking for a high amp short that is trying to find the path of least resistance and the coil is the weak point. Electric clutch shorted to the crankshaft of the engine or something similar or a faulty engine ground. Stator shorting out under the flywheel feeding power to the coils. something is electrically goofy there some place.

The problem is external to the ignition modules. the modules don't have the electrical output to cause that type of damage.

 

[slomo]

See if you have 12 volts on the coil metal case body. That will blow the coil out. Something 12 volts is grounding out on the coil which mounts to ground.

slomo

 

[Hammermechanicman]

What is the spark plug gapped at?

 

[Rivets]

This may be the dumbest questions I’ve asked in a long time but, have you checked to make sure the cooling fins are very clean around the coil? Also, is it occurring only on one side? Could the coil be mounted upside down? Couple of observations from my feeble mind. To me it looks like something is rubbing on the coil. The kill wire tab would normally go down. Normally that kind of heat generation will short the coil out, before melting occurs.