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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

Wico C on John Deere


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  #1  
Old 06-22-2019, 06:26:35 PM
Alan R Alan R is offline
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Default Wico C on John Deere

Hey guys, I really need some help. I am working on a John Deere H with the Wico C mag. I get plenty of blue spark, but both plugs fire at the same time. On every impulse both plugs will fire. I put on a new cap and rotor hoping that that was the issue, but same result. I changed one wire, although it was an old one, and still no change. Any ideas on where else I can look?
Alan
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Old 06-22-2019, 11:33:09 PM
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ulgydog56 ulgydog56 is offline
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Default Re: Wico C on John Deere

yup that don,t sound right, i'd have the mag checked over by a expert unless you know what your doing, there's a lot going on inside of a mag......
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Old 06-23-2019, 10:18:56 AM
radiodoc radiodoc is offline
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Default Re: Wico C on John Deere

I am by no means even close to being an expert on JD tractors or mags, but perhaps the impulse timing is not set right. Here is a couple links about JD magneto timing: https://www.youtube.com/watch?v=HmmkAZ3cKvo & https://www.youtube.com/watch?v=U-Qenm71rtc
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Old 06-23-2019, 03:02:46 PM
Alan R Alan R is offline
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Default Re: Wico C on John Deere

Thanks guys for the input. I believe the mag is okay but the distribution of the spark is where the problem is. The timing issue would be a problem if on the tractor, but this is on the bench. The mag is mounted to a vise and the plugs are clamped to the same vise.
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Old 06-24-2019, 09:07:32 AM
radiodoc radiodoc is offline
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Default Re: Wico C on John Deere

Alan R I just have to ask. Has this mag been working on your model H John Deere and just quit?
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Old 06-24-2019, 09:41:39 AM
Kirk Taylor Kirk Taylor is offline
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Default Re: Wico C on John Deere

Quote:
Originally Posted by Alan R View Post
Hey guys, I really need some help. I am working on a John Deere H with the Wico C mag. I get plenty of blue spark, but both plugs fire at the same time. On every impulse both plugs will fire. I put on a new cap and rotor hoping that that was the issue, but same result. I changed one wire, although it was an old one, and still no change. Any ideas on where else I can look?
Alan
That is definitely odd. Usually, when two plugs are attached to a single source one plug is preferred over the other, so only one will fire. It sounds as if the plugs are in series, electrically. In other words, the path to ground is through the other plug and somehow back to the coil instead of through the magneto body. I'm not sure how that could happen, but I've seen some really bizarre things over the decades.
Use a multi-meter to check continuity of the secondary winding to the magneto case. The secondary ground should be tied to either the primary ground or the core, but.........
Be sure to let us know the answer when you figure it out.
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Old 06-24-2019, 02:22:48 PM
Alan R Alan R is offline
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Default Re: Wico C on John Deere

RD, I got this as a non-running tractor with the assurance it was running when parked. I believe that. As I stated this is being tested off the tractor. The tractor is somewhat disassembled and not ready to run. While checking the mag is when I ran across the issue.

At our work session at the grove today I took the mag along so everyone could opine. The next thing I am going to check is to see if when the mag is mounted on the tractor both plugs still fire. When turning by hand there is a "spring back". We are wondering if as the engine spins that won't occur and therefore not fire both plugs.

Another thing we wondered is if the tractor could run like this. Like a wasted spark ignition on a hit and miss engine. If the cylinder is charged with fuel it fires if not "so what".

Now that I've started this As Eldon says "Inquiring minds want to know". I'll keep you posted no matter how foolish it makes me look.
Alan
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Old 06-24-2019, 07:27:12 PM
Alan R Alan R is offline
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Default Re: Wico C on John Deere

Well, the magneto works as it is supposed to. I don't know why but when I put it back on the tractor each plug fired independently of the other. I wonder if anyone else ever bench tested their mag and why it was never noticed. Just lucky I guess. I took the new cap and rotor back off and put it on a shelf until I forget and do this again.
Thanks again for the comments and interest. Sorry I couldn't find a definite cause,
Alan
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Old 06-24-2019, 08:23:56 PM
landreo landreo is offline
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Default Re: Wico C on John Deere

It is essentially impossible for a Wico C to fire both plugs at the same time. One plug will fire first and drain the current before the second could fire if for some reason both were trying to fire together. There are duel spark coils that will fire both plugs together by going through one plug to the other and out the second plug back to the coil. I have one Farmall cub engine running like that. The Wico C cannot be shorted, broken, otherwise missasembled to give that duel spark setup. Carbon tracts, bad rotors, bad distributor caps etc.. will not do that.

Why is it happening i.e. both plugs firing at the same time? Simply put, it isn't. Both plugs may look like they are firing at the same time but they are not. One fires and 180 degrees later the other fires. The effect of friction by the Wico C bronze bearings, impulse pawls, and the magnetic "friction" of the rotor would normally keep the rotor from spinning enough on a work bench setup for the second, 180 degree later, firing to occur but not always. Sometimes the impulse spring will spin the rotor fast enough so the second, 180 degree later, firing will occur. That is not a problem when installed since the lugs of the impulse are essentially locked to the engine rotation and the rotor can only spin separate from the impulse lugs the amount of the lag angle. On a bench or vise setup the impulse plate and hence the rotor can spin much more unrestrained and fire a second time.

You can remove the distributor cap, ground the wire out of the coil so it does not fire and trip the impulse once. Ideally it would move the rotor less than 180 degrees so it could only fire once. I expect, on your mag, the rotor will move more than 180 and is really firing both plugs sequentially not simultaneously.
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Old 06-24-2019, 10:35:04 PM
radiodoc radiodoc is offline
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Default Re: Wico C on John Deere

Perhaps the mag frame, plugs and all wasn't grounded good together...good to hear that you finally figured out it will work correctly on the tractor.
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