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Cub J4 Magneto

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WayneMo

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I am working on a J4 mag given me without knowing if it is good. I cannot find the beveled 2 teeth on the rotor. I have looked at it for an hour and simply cannot see where 2 teeth are beveled. There is a nice raised mark on the drive gear but nothing on the rotor teeth. Could the teeth have worn off the bevel? Could it be another rotor that uses the terminal to align with the drive gear?
I need for someone to look at one with beveled teeth and tell me where they are relative to the terminal looking at it from the teeth side at the 12 o"clock position.
Also I was unable to remove the 11/16 nut on the lug end. Is there a trick to do this? If I hold the lugs and turn the nut, it just winds up the spring inside and I stopped before it loosened. I assume it is a right hand thread.
 
I found a photo of a line on the rotor to match up with the mark on the drive gear. I was looking for 2 beveled teeth on the rotor instead. So now I guess that issue is resolved.
I still need to know how to remove the 11/16 nut on the impulse coupling. Thanks.
 
Should be a hole or a slot to stick a tool in impulse coupling. I think I always used an allen wrench on the H4 but not I'm not into J 4 magneto's .
 
I thought I might look inside and clean it out and add new grease. I put it back together after cleaning and adjusting the points and got a good spark when I turned it. Don't you think I should go inside the impulse area?
 
There is a square hole in the drum like impulse but it is not easy or clear as to how to employ it. I guess if I had a helper I could put something inside the square hole and force the nut off after it stopped moving under spring load. Sure seems like a difficult task for something so simple. Surely there is a trick to it!
 
put a heavy leather glove on your left hand and get a gold hold on the impulse dome. Use a battery powered impact to spin it off. If it is too tight, get a large channel lock pliers to catch the ears while loosening nut. Pay attention to the way the lock washer and index washer are in place. Next comes the hard part, that impulse is on a tapered shaft and will be tight. You need a puller that screws into the hole to remove the impulse. I have done it using a couple screw drivers and a medium hammer, but I also ruined a tight one trying to remove it.
 
I would take it apart. You will find the weights rusty, cruddy and most likely worn out. I often dress the ends of the weights back to nice and square and then, if like a H4 magneto, I knock the pin out that weights contact and turn it to a new unworn spot. If holes in weights and or pins are worn too bad, it will require some type of repair to get a good working impulse.

I used to have a box full of old magnetos in the shop and after parts became out of this world expensive, I would go through them and pick out the best I had left. Even the springs get weak as rust is the biggest enemy of any spring.

Yes an impact wrench will work but back in the day, who had impact wrenches, thus other methods were needed.
 
How to clean the impulse with kerosene? Do you mean after you remove the nut and impulse or just dunk it in kerosene?
 
I finally got the 11/16 nut off the impulse coupling. There is an "R" stamped on the dome, what is that for if anything?
I found a small gear puller that fits on the impulse plate inside but I cannot get the plate off even with the puller. I am afraid to tighten it further and am leaving it sit overnight to see if it will break loose. I tapped on the puller bolt with a small hammer which usually will break a tapered fit loose to no avail. It is hard to believe that anybody could remove the plate with only 2 screw drivers!
I am proceeding cautiously to avoid breaking anything but there appears to be little beneath the plate except the 2 "dogs" that swing in one direction to engage the spring, which seems to be in good shape.
 
It is difficult, but you can do it with 2 screw drivers to put pressure on the outsides like a puller, and tapping on a nut on the center shaft. I did ruin an impulse doing that one time though. Bent the plate. The R on the plate means Right Hand rotation. Those were also made for tractors that the shaft turned in the opposite direction, and the were marked L (Left hand rotation).

The original puller screws into where the nut was removed, and a center bolt pushes on the shaft to remove it. Pulling on the outside can damage it. There is a big compression spring inside that plate that spins the shaft when it turns far enough to release the dogs. The dogs are on a separate plate.

If you decide to remove the dogs look the dog springs over very carefully as to how they are installed in the dogs and mounting plate. They do not go back the way they look. that they should.
 

There was a guy selling the special puller made for the J4 and H4 paw plates. He's website was rebuiltmags.com. The puller was priced at $30. He might still have one.


I have removed many paw plates with a small gear puller and heat.

Screw the puller up tight. Then stand off to the side and heat the hub with the torch. The paw plate will come off with a "Pop" and "fly across the shop with the puller. This is why you don't stand in behind it while heating the hub.
 
I do not understand how the puller works. There is only the threaded shaft and nothing around it to
pull or push upon. I have the domed piece off and have the long spring curled inside it and looks
to be assembled back on only one way. The flat plate has the swinging dogs on the underside and I
can; see nothing else without removing the flat plate. I see no way to attach a puller other than
the usual 2 jaw puller gripping the plate edges and pushing on the threaded shaft extension. I am
afraid I will bend the plate if I overdo the puller.
I see large screw heads inside and wonder what they will expose and if I will need to remove
them. I sure wish I had a good diagram or photo of the insides. s
s You sound like you are very familiar with these and I appreciate your advice. It would be
nice to talk to you perhaps.
 
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