Weak Spark

Sun Mar 11, 2012 8:53 am

:help: My magneto generated a very weak spark, so I replaced the coil and condenser. I can’t say that there has been any improvement in the spark generated. If I place a spark plug wire directly in the coil cover, I get a visible but very weak spark. However, I get no spark at the magneto cap. I am wondering if the magnet in the unit can lose it’s strength over time (absent some physical damage). Any ideas about what I may need to do to get a decent spark out of this magneto? :help:

Re: Weak Spark

Sun Mar 11, 2012 9:16 am

The magnets can lose their strength. When mags were commonplace there were re-magnetizers around. I just did a quick google search for "how to re-magnetize a magnet" and there were several links.
This is one of them:

http://www.ehow.com/how_4878360_old-mag ... gnets.html

Re: Weak Spark

Sun Mar 11, 2012 10:01 am

I'll be watching this post closely to pick up some pointers :sick: I acquired a small magnet charger for my "stationary engines" and thought the cub magneto magnet could also be recharged with it too. I quickly noticed the mag setup is entirely different and was told it's supposed to be a "permanent" charge magnet and never needs charged, but I still have my doubts and agree with Bigdog. I did a search on ebay back then for a tester(I forget the name) to see how much charge various magnets had, but I never bought one. It also gets a little confusing trying to determine which is N and which is S because of the way the mag is designed. My compass picked up the direction, but trying to get the charger adapted and then knowing how much was enough was the big issue. I didn't want to remove any charge if the charger was too small, if that's possible with a so-called "permanent" magnet.


Re: Weak Spark

Sun Mar 11, 2012 10:56 am

I have never heard or read where a Cub or any letter series tractor having to have the Mag recharged due to "weak magnets".
Have you changed the coil? The weak spark, is that with or without the tripping the impulse coupling?

Re: Weak Spark

Sun Mar 11, 2012 11:29 am

I don't see mention of doing anything to the points. If not, either carefully clean or replace them.

IH used alnico alloy magnets in the H series and J-4 magnetos. The older hard steel magnets tended to loose magnetism and needed to be recharged periodically. The alnico magnets are generally considered to be truly permanent, much more so than the iron magnets.

Re: Weak Spark

Sun Mar 11, 2012 12:26 pm

I don't know any way to recharge the AlNico magnets in the J4 magneto. They are "supposed" to be permanent, and usually are. However, Joe Howard had one that had lost its magnetism. I can only assume that happened from a previous owner's "mishandling" of that magneto, probably getting it near another source of magnetism. Whenever you remove the shaft from a J4, it is supposed to be inside a protective "sleeve", just to insure no harm comes to it.

I agree with Jim, you didn't mention points, so be sure they are addressed as well. If you still don't get a good spark, ship me that magneto and I'll fix it for you.

Oh yeah, just to be sure, the points in a magneto are gapped to .013", while a distributor is gapped to .020". Check it twice.

Re: Weak Spark

Sun Mar 11, 2012 9:24 pm

I have not replaced the points, but they are in fine shape and properly gapped (.013). Has anyone actually had a J4 magneto re-magnetized? If I cannot get a decent spark, can the magneto be converted to use a battery actuated coil, or is a distributor required?

Re: Weak Spark

Sun Mar 11, 2012 9:33 pm

Like I said above, I've never heard or read of a J4 Mag being remagnatized. The Mag can be converted to act like a distributor, but it is not the direction I would recommend. You loose the benefits that the Mag inherently has and won't gain the benifits of the full distributor either. You end up with a ignition system that is sub par to both.
I would recommend fixing the Mag you have, or completely swapping out for a distributor.

Re: Weak Spark

Sun Mar 11, 2012 10:23 pm

Raymond, I went back down to my basement after my last post. I fiddled a little bit more with the mag and realized that may not have quite the problem that I thought. I have been testing the mag with the coil to magneto cap cable from my new ignition wire set, however, the wire from cap to test spark plug was from an old automobile wire set. The old set was a resistor type with carbon filiment rather than copper wire. If I test directly from the coil with the copper wire, I get a good spark, but I have no spark going through the rotor and cap. My rotor seems to have a good bit of free play back and forth. I wonder if it could be worn to the point that it will not properly transmit the spark from rotor to cap and on to the spark plug.

Re: Weak Spark

Sun Mar 11, 2012 10:30 pm

It could very well be. Check the condition of the teeth on both the rotor and the pinion gear for wear, and make sure that they are properly installed and "in line". Check the cleanliness of the inside of the cap and all the conductive parts.
Copper core wires are a must as you have found out!

Re: Weak Spark

Sun Mar 11, 2012 10:43 pm

Does the rotor and pinon gear have to be "in time"? Is there some type of mark on the two components which must be aligned when installed? (I have not yet removed the rotor from the pinion gear. Thanks

Re: Weak Spark

Sun Mar 11, 2012 11:05 pm

thiggy wrote:Does the rotor and pinon gear have to be "in time"? Is there some type of mark on the two components which must be aligned when installed? (I have not yet removed the rotor from the pinion gear. Thanks

Yes, they have to be in time and there is a timing mark on both.
(photo courtesy of Rick Prentice)

Re: Weak Spark

Mon Mar 12, 2012 10:20 am

Thanks, Raymond. I was hesitant about removing the rotor and pinion gear till I knew that I would be able to re-assemble correctly. Stanley

Re: Weak Spark

Mon Mar 12, 2012 10:47 am

To reply to what little I know about re-magnitizing the magnet in a mag. I traded my original mag a few years ago to a man named John Jones in McMinnville TN. I was going to have him rebuild mine, but since he had a fresh rebuilt one on his shelf, I swapped out with him to keep from making another half day trip there and back. But anyway, while I was in his shop, he showed me a "magnitizer" that was from an old John Deere dealership in his area. According to him, this is what he used when the magnet lost it magnatism.

Other than that, I have no personal knowledge how effective the process is.

Re: Weak Spark

Mon Mar 12, 2012 5:37 pm

Again, magnetizers were necessary for the older "ferrous" mag cores. The J4 uses an "AlNico" alloy that is considered a permanent magnet. I, like Raymond, have never heard of anyone "recharging" a J4 core, nor would I have a clue how to do it. If you really do find a damaged one that has no magnetism any longer, replace, it. Call me, I have lots of cores....