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Discussion Starter #1
Okay I have a problem with the magneto on my LI. Every so often the impulse will not engage. I do have plenty of compression, but what it has started doing is not engaging at all for several rotations and then suddenly it will engage. it has not started
 

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+1

I've seen a number of wicos where the impulse mechanism just gets gummed up. I think just from neglect. At least a couple of them I've been able to free up by taking off the cover around the drive and spraying solvent and thin oil in there.
 

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I agree, it is usually dirt, go easy on the oil as it will attract dirt. Especially if the cork gasket is broken. Todd White sells those cork gaskets,

http://gtgravelyparts.com/zenithcarbs.html

Occasionally the impulse arm will become magnetized and stick in the run position.

One member here, I think it was Hamer, had a Wico with the incorrect pre-wind on the drive cup spring. With a Wico on the bench, it should be almost impossible to trip the impulse arm by hand. I need a small crescent wrench while bench testing, and remember to short the output to the case, or through a spark plug grounded to the case. Turning the magneto over without a return path for spark will stress the coil windings, keep doing that and it will short out the windings.

Roger,
 

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I think it was roger who made mention that the impulse coupling can potentially become magnetized on higher hours magnetos. That if you put some small lathe turnings or a paperclip up against the coupling and it sticks, than it is. A local machine shop would be able to demagnetize the part for you if that were the case. But chances are hamer is right.
 

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Discussion Starter #7
well it was a combination of dirt and worn parts on both magnetos, so I need to fully rebuild one of them and replace the trip lever on the other. Does anyone have information on the factory specs for clearance of the armature shaft( needs new bushings)
 

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Gravely Model L Guy
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I have a magneto if you want one, it works well, send me a pm if interested.
 

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Old Iron Connoisseur
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thanks for your offer but I want to know how to rebuild the magneto's
I respect the ambition but be prepared to spend some money... to fully rebuild a magneto properly. The sad fact is that there are few people left that can recharge the magnets and such. The impulse coupling spring can also make for an interesting time I'm told.... if you do rebuild it please get lots of pictures. There is tons of information about building charging coils and such so it is not impossible. :thThumbsU
 

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Standard Magneto, the people who bought Wico, will recharge Wico rotors.

http://standardmagneto.com/

The last one I had recharged cost twenty-five dollars. That might seem a little steep but you probably will spend very big bucks trying to build your own recharger, maybe thousands, there is an enormous amount of copper wire in them. I have no plans to build my own.

A Wico rotor must be removed from the case and then the impulse mechanism removed from the rotor. In order to ship a rotor, it must have a shorting strap around the magnets. Do observe the lag angle timing marks before removing a rotor from a magneto case.

Magneto shorting  strap.JPG

A rotor left outside of a magneto case without a shorting strap will lose magnetism, the less the strength of the magnets in the rotor, the less the strength of output spark. Aircraft magneto rotors have to be recharged and re-certified every ten to fifteen years.

Another magneto biggie is the coil. On a Wico magneto there is a quick condition check if you have a good ohmmeter. Between the end of the spark wire and the magneto case, you should read 4500 to 6500 ohms. If you get a higher reading between the tractor chassis and the end of the spark plug wire, then your magneto is not properly grounded.

If both readings are higher, there may be a bad connection between coil and the end of the wire. An open reading would indicate an open or failed coil.

If your reading is less than 4500 ohms then maybe some of the windings in the coil have shorted out. That can occur when bench testing a magneto with no return path for the spark. Always keep a shorting wire or spark plug wire with plug grounded to the case when bench testing magnetos.

Roger,
 

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Standard Magneto, the people who bought Wico, will recharge Wico rotors.

http://standardmagneto.com/

The last one I had recharged cost twenty-five dollars. That might seem a little steep but you probably will spend very big bucks trying to build your own recharger, maybe thousands, there is an enormous amount of copper wire in them. I have no plans to build my own.

A Wico rotor must be removed from the case and then the impulse mechanism removed from the rotor. In order to ship a rotor, it must have a shorting strap around the magnets. Do observe the lag angle timing marks before removing a rotor from a magneto case.

View attachment 250059

A rotor left outside of a magneto case without a shorting strap will lose magnetism, the less the strength of the magnets in the rotor, the less the strength of output spark. Aircraft magneto rotors have to be recharged and re-certified every ten to fifteen years.

Another magneto biggie is the coil. On a Wico magneto there is a quick condition check if you have a good ohmmeter. Between the end of the spark wire and the magneto case, you should read 4500 to 6500 ohms. If you get a higher reading between the tractor chassis and the end of the spark plug wire, then your magneto is not properly grounded.

If both readings are higher, there may be a bad connection between coil and the end of the wire. An open reading would indicate an open or failed coil.

If your reading is less than 4500 ohms then maybe some of the windings in the coil have shorted out. That can occur when bench testing a magneto with no return path for the spark. Always keep a shorting wire or spark plug wire with plug grounded to the case when bench testing magnetos.

Roger,
It is posts like this that make me think we need a magneto sticky thread. :) Or expand Roger's magneto timing sticky.
 

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I Love All Color Tractors
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It is posts like this that make me think we need a magneto sticky thread. :) Or expand Roger's magneto timing sticky.
With Roger's blessing, I can copy his post over to the timing sticky. I think it would be a great addition.
 

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If possible it would also be great to incorporate some of the many past posts about basic timing techniques for the less technically inclined.
 

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I Love All Color Tractors
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After looking back and rereading this thread, it is better for it to be a sticky of it's own.
 
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