Magneto Magnet Questions

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jagiven
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Magneto Magnet Questions

Post by jagiven » Tue Feb 26, 2019 10:57 pm

While cleaning up the magneto magnets this evening, we found one cracked magnet, and with the lightest tap it broke. Looking in the catalogs, you can not purchase a single replacement magnet. Have any recommendations for a replacement? I was thinking of calling on Andy Loso.

Also is there any reason NOT to glass bead blast them?

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Steve Jelf
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Re: Magneto Magnet Questions

Post by Steve Jelf » Tue Feb 26, 2019 11:52 pm

Most of the dealers have parts that aren't listed in their catalogues. I would call around and ask. I don't see any reason not to blast. Also, before you charge them, whack each one against a vise or an anvil a few times. You want to weed out any that are cracked. I would do this before replacing the one that's already broken, just in case you turn out to need more than one.
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Re: Magneto Magnet Questions

Post by Adam » Wed Feb 27, 2019 2:15 pm

Ford magneto magnets are basically a hard tool steel. They are made of a very hard steel because it was the optimum material to hold a good magnetic charge for a long time. Because the steel is hard, it is also brittle. If you put a good Ford magnet in a vise and squeeze the ends together, it will break. If you put a similar piece of hot rolled, cold rolled, stainless, or various other grades of steel in a vise, they can be bent without breaking. My advice is to never use any “potentially destructive” method to check Ford magnets. I have seen “break testing” or “hammer testing” of magnets recommended on the forum several times over the years and I respectfully dissagree with the method because it is very likely to cause more defects than it finds. Hammering a magnet against a larger metal object will break the magnet that is “just about to fail”, but it also stresses and fatigues the seemingly good magnets in a way they were never meant to be treated. What may have otherwise been very good magnets before they were “fatigue tested”, may be “just about to fail” after they are pounded against something.

In industry, the method of evaluating a part that you still wish to use is called “Non Destructive Testing”. In checking Ford magnets there are 2 basic tests the average hobbyists can use: Visual and Ring-test. Magnets should be solvent washed to remove all oil, grease, and loose dirt. They can be manually scrubbed with a wire brush and/or abrasive blasted. A gentle abrasive such as glass bead at a medium pressure works best. The first test is a good, careful, visual examination of each magnet. If you don’t have excellent eysight, then use a big magnifier or have someone help you. Generally speaking, MOST defects that ever may cause a magnet to fail in use can be SEEN on a clean magnet. An alternative visual test if they were solvent washed and immediately abrasive blasted, is to not remove the haze of abrasive dust and lay them out on a table in a single layer and leave them undisturbed for a couple hours to overnight. Upon a close visual inspection, imperfections that held traces of the oily solvent thru the blasting process may show up as small oily lines and be easier to spot. The second basic test is the “Ring Test”. The magnet can be hung by its v from a piece of string long enough that your hand is at least 6” above the magnet. Then tap the part of the magnet that would be against the brass clamp screw with a very small ball pien hammer or similar object. Only tap the magnet enough to cause it to ring like a bell. Hold it up to your ear and it should hum like a tuning fork and take several seconds to fade. Any magnet that only produces a dull thud is generally cracked 1/3 of the way thru or more. Any magnet that rings a noticably shorter duration than the rest should be noted as “suspicious” and probably best off to replace.

In addition to the simple tests that the average hobbyist can perform at home, there are two professional tests. One is a liquid dye penetrant test. And the other possibility is Magnafluxing. I would not recommend regular Magnafluxing for these magnets, but there is a pulsed-direct current Magnafluxing yoke on the market that is preferably used with a liquid particle solution and can be used on these magnets without risk of changing their original poles.

The “professional” tests are overkill in my opinion, unless maybe you are working on a ‘08-‘11 with great original parts and desire to “pay for additional insurance”. I own the proper Magnafluxing setup and when I first purchased it 10 years ago I experimented with its effectiveness on magnets and found the visual and ring-test to have about the same effectiveness.

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Re: Magneto Magnet Questions

Post by Steve Jelf » Wed Feb 27, 2019 3:03 pm

Ford magneto magnets...about the same effectiveness.
Excellent! Thanks.
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Re: Magneto Magnet Questions

Post by George Andreasen » Wed Feb 27, 2019 5:10 pm

Adam's excellent post details the best way to go. To my knowledge, there are two crack detection tests: Magnaflux and Magnaglow, both used in aircraft engine work. Probably the best way to find such a service would be to start at your local airport, and ask the aircraft mechanic. The interesting thing is that both tests require the part to be electro-magnetized. Your "parts" are already magnetized! ;)

Edit: Correction on those names........one of them is "Zyglo" if memory serves......but I forgot which!


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Re: Magneto Magnet Questions

Post by Adam » Thu Feb 28, 2019 10:40 am

I put a magnet in the press yesterday to illustrate how easily they break. The pressure gauge on the press never rose off its stop. The height of the ram is where the magnet shattered. The un-broken magnet is there for comparison. Note that the magnet didn’t just break... It shattered.
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Re: Magneto Magnet Questions

Post by Norman Kling » Thu Feb 28, 2019 12:09 pm

I agree with the above methods of testing. One other thing to note is every other magnet is of opposite polarity so that when assembled on the flywheel they will have two north poses and two south poles together all the way around the flywheel. So you need to know the polarity of the magnets you are replacing. Note, most swap meets have some magnets for sale and also you will find some members of a local club who have spare magnets which they would likely either sell for a small amount or donate to you. You should re-magnetize all the magnets in the same polarity as they were originally charged to get the longest lasting magneto. The sets you purchase from the vendors have been tested for cracks and re-charged ready for installation.
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Re: Magneto Magnet Questions

Post by R.V.Anderson » Thu Feb 28, 2019 12:43 pm

A variation on the method that Adam describes is to soak clean magnets in mineral spirits for a half minute, then wipe them dry. Lay them out and sprinkle a light coating of baby powder, talc or starch, all over but especially into and around the vee. Cracks will show themselves as the solvent leaches out into the powder.


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Re: Magneto Magnet Questions

Post by Bill Kerndt » Fri Mar 01, 2019 1:25 pm

Adam Excellent "learning" article. Thanks for the informative article on magnets.

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Re: Magneto Magnet Questions

Post by HalSched » Fri Mar 01, 2019 1:52 pm

Thanks Adam. Question: Why do the magnets crack or break in the first place?? Their only resistance is oil and they are secured against the fly wheel..


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Re: Magneto Magnet Questions

Post by Adam » Sat Mar 02, 2019 11:47 am

That’s a darn good question. Here are a few possibilities:

I have seen a few magnets that had cracks starting at what looked like a little fold or defect in the inside corners, (possibly from being formed too cold?). I’m not sure if they were bent to shape hot or cold, but they would have been hardened (heat treated) after forming, so could have been subject to abuse before they were assembled.

Ford used a soft face hammer to slightly adjust magnet heights on the flywheel, so its possible they were damaged then, but I feel that is unlikely, because if Ford ever traced any major failures back to that step, they likely would have changed the way they did it AND the way they suggested it be done in service.

A more likely explanation is that flywheels that were serviced were treated roughly and heights were adjusted by beating with a regular hammer instead of tapping with a soft face hammer because the guy doing the job just didn’t really understand what he was doing.

The most likely explanation, and the one thing that I think is probably the largest cause is: Debris strikes at some point during the life of the motor... Something as small as a band washer or an accessory oil dip that got loose, was grabbed by a magnet, and tumbled around for a couple seconds before tucking itself away where it will sit without moving again, sometimes for decades.

I took apart a decent looking flywheel from a ‘15 a couple months ago. Everything looked great, but when I removed the magnet hardware, half of the magnets were broken. It seems that most of the time they break in such a way that they stay secure in their positions and do not move, or cause further damage.

Probably one in every four or so flywheels I’ve disassembled has had at least one partially cracked, if not totally broken magnet.


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Re: Magneto Magnet Questions

Post by Scott_Conger » Sat Mar 02, 2019 12:12 pm

(Material deformation at manufacture + Thermal cycling) * Age = Stress Risers
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Re: Magneto Magnet Questions

Post by kelly mt » Sat Mar 02, 2019 4:30 pm

I found two magnets broken on my last motor. I could see the break from the metal fuzz collected along the edges of the break. They stood out pretty clear.
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Re: Magneto Magnet Questions

Post by TonyB » Mon Mar 04, 2019 11:51 pm

You are so lucky that they didn’t escape. I have had two engines where the magnets let go and hit the magneto coil with horrible results. Unless you remove all the magnets and have them magnofluxed, I don’t know how you can avoid the potential for a problem. Of course you can remove all sixteen and run on a distributor but that will get me banned 😊😊
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Re: Magneto Magnet Questions

Post by kelly mt » Tue Mar 05, 2019 11:14 am

Tony, yes this motor has a Bosch front plate distributor. So I did remove the magnets and put on slingers. At least when they come off the damage is minimal.

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