Is my coil fried ??

Kestrel in CT · Mar 28, 2009

Can anybody describe a quick 'n easy way to test a 12 volt coil ?

I have a multimeter but confess I'm not sure how to use it for this. Its a 3 ohm coil thats been on my Case tractor for a couple of years now.

I suspect the coil since after replacing the points today, I still had no spark.

Wife left the ignition on the other day, battery drained and smoked the points pretty good. At least I think that's what did it.
Thanks guys...

Anonymous-0 · Mar 28, 2009

Are the points opening and closing? Check for that with a light across them.

Then pull the coil wire from the center tower of the distributor. Hold it 1/4 to 1/3 inch from the engine block. Cause the points to close and open. Each time the points open there has to be a blue spark. If there isn't, the points may not be making contact, the wiring from coil to points my be bad or the condenser may be bad. If all those are good, the coil is bad and you can't check it with a normal meter. This spark test is what works. You don't make this test with the light across the points. That will kill spark on a good coil.

Gerald J.

John B. · Mar 28, 2009

That's the first thing I ask a customer when they come to me with a problem. I ask them has it been worked on lately and what work was done?

If you just replaced the points I would unhook them to test the coil with a good power source. Look for any wire inside the distributor now for it shorting to ground or touching the frame of the dist. I've had that happen my self after installing new points. It's very easily done.

Since it ran before you installed the points and now it doesn't after you installed them I would vote to say you have a bad connection or the points are not closing to allow any current to flow thru the coil. There are many tests you could do with your ohm meter but too many to mention here.

Let us know what you fine.

John

old · Mar 28, 2009

Pull the cap off and then by hand open and close the points. Do you get a spark at the points?? If you don't clean them, new from the box they often have a coating of oil on them and that is enough to cause you problems. If you have a spark there then pull the coil wire from the cap and hold it close to the block and open and close the points by hand. If you have spark at the points but none from the coil wire then you stand a good chance the coil is bad
Hobby farm

Kestrel in CT · Mar 28, 2009

I'll have to wait until the morning so I can buy another set of points. My brand new NAPA points were the biggest piece of garbage I've ever seen.

The flimsy breaker point spring consisted of the thinnest single piece of copper I've ever seen. It sheared off upon assembly. So now I located a pair with the reenforcing steel spring, made by Blue Streak I think, from a different NAPA dealer !

Thanks all for the tips......I'll be back tomorrow with an update.

ken in texas · Mar 28, 2009

spring should not be copper, maybe it is copper coated spring steel,it should not break,maybe it got so hot it lost it.s temper,like I do sometimes(not anymore tho)

Wesley Stephens · Mar 28, 2009

I have had good success checking the resistance. I have had several coils that were fine when they were cold but would heat up and build resistance.

Bob · Mar 28, 2009

Yeah, RIGHT!

old · Mar 28, 2009

Well yes if you know what the resistance should be and you have a good enough meter that is calibrated so you know in fact it is reading what it should. The common man will not have that and also do you have any idea what the resistance should be on say a 6 volt coil or a 12 volt coil. I know I sure don't know the resistance value and most people have no idea either. So my way works well ya it is not 100% but it does work most of the time

Is my coil fried ??

Kestrel in CT

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John B.

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old

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Kestrel in CT

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