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Magnets


J A Boggan's Avatar
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11-01-02, 03:13 AM   #1  
J A Boggan
Magnets

What is a good way to tell if the strengh of a magnet is O.K., in particular: (1) flywheel magnets for ignition (2) Flywheel magnets for alternators (3) Starter field magnets (ceramic magnets). Also, if you run into one that you suspect as beenlng 'weak', is there any way to rejuvanate the magnets. What are you chances of running into 'weak magnets'. These magnets are the ones on small engines.

 
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11-01-02, 06:23 AM   #2  
kingbee
For flywheel magnets ( for ignition ) take a small screw driver and hold it losely with your fingers , move it slowly towards the magnet , if the magnet snatches it then it's strong enought . I don't know for sure , but I'd guess the same is true with the others . I've seen some very old flywheels , can't recall seeing any that the magnets weren't strong enought to work for ignition . But I'm sure there are some out there somewhere .

 
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11-01-02, 01:40 PM   #3  
MARK1CAROLINE
I have been in the trade for years, what makes you think the magnet is a problem? I personally have never seen a trouble some magnet

 
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11-01-02, 07:56 PM   #4  
J A Boggan
Just trying to start up a lawnmower business. I just wanted to try and cover all the bases.

 
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11-01-02, 08:28 PM   #5  
Hello J A Boggan!

I've never seen a bad magnet on a flywheel....ignition, or charging, except for broken or loose magnets. I suppose it's possible, but they don't generally go bad.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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11-01-02, 10:01 PM   #6  
J A Boggan
Thanks fellows for your rapid response. I have never run into this either but I feel better about it, knowing that you all haven't ran into this problem either.
Thanks again!

 
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11-02-02, 02:39 AM   #7  
Tcumcman
Magnets

Jack,

I agree with Cheese that magnets rarely (if ever) go bad. They
will, over time, come loose sometimes causing damage to the
stator/alternator. I've seen folks "glue 'em" back in with JB Weld
or some other type of cold weld epoxy. Sometimes they come
loose again, and sometimes they stay put. Tecumseh has only
suggested using the "screwdriver method" to test a magnet. If
the magnet draws the screwdriver blade over to it....it's GOOD.
Not too much to worry about with magnets, Jack. See ya !!

Tcumcman

 
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11-02-02, 05:37 AM   #8  
MARK1CAROLINE
I have just seen a bad magnet on a briggs engine cause by a hapless user trying to engage the starter bendix using a hammer. Of course as we all know this causes the magnet inside the starter motor to break up come loose and spin the guts out of the windings. Tell tale sign's are paint chiped off of the centre section of the motor body.

 
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11-03-02, 12:45 AM   #9  
Now starter magnets are another story. I have seen MANY broken by the method you just described. Usually when someone whacks the starter, it breaks a field magnet and the starter turns just enough to rip and cut the armature windings to pieces. $110.00 or more mistake. Of course, it gives me a chance to sell a rebuilt starter, LOL.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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11-07-02, 12:58 PM   #10  
buttlint
J. I have seen one bad magnet in my career. That was on a new Toro 3650 snowblower, and that was last season. The screw driver test seems to me to be pretty subjective. The only way that I suspected a weak magnet, was that it "seemed" weak compared to others that I have tested over the years. Fortunately, I had a ton of those flywheels on the warrenty rack to compare the pull. It had about 1/4 of the strength of the others, but still did attract a screw driver. I think the tecumseh test is a bit to vague to make a call on. They dont tell you whether to use a #3 snap-on philips or #1 craftsman flat blade

 
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11-07-02, 05:24 PM   #11  
J A Boggan
buttlint,
What type of difference did the stronger maget make? Did you see a large improvement on your spark?

 
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11-08-02, 04:36 AM   #12  
buttlint
J.
It's hard to judge with a resistor plug, because the they put out such a short arc. I have several methods for checking, and they are all pretty primitive. I use an older plug, like a CJ-8 instead of a RCJ8. I also have a Briggs standard issue tester. I have an older tester that uses a plastic chamber that is basiclly a spark plug with the electrode enclosed in a chamber that I can pump and pressurize. I sounds mickey mouse, but has saved my butt many times. The theroy is that the pressurization is more like the condition of the cylinder when the plug fires. For the sake of any other way to describe it, it puts the plug under a load.
More than once, a plug or Briggs tester sparks merrily away, indicating that the ignition system is in tip top shape, but the symtoms are still telling me that I have an ignition problem. When I use the pressure tester, and then I have no spark, then I know for sure where the problem lies.
In the case of the Toro 3650, the spark "looked" fine. It was hard to tell if it was "intermintent" or not. It started hard and when it ran it missed. I checked all the usual suspects and every thing was fine. I even used my trusty pressure tester. I checked the air gap, and even tried a new module.
Up in our area(MI) we have done a ton of these flywheels on these units, because of a ring gear problem that these units have had since thier introduction. Since there was nothing left to check or test, the magnet was the only thing left in the system to suspect, and other than producing a magnetic field, thats all they really do.
Clutching at straws was what this problem led to, and just for giggles I decided to compare the pull of the magnet with those that I had sitting on the warrenty rack. Sure enough, there was a noticable difference. There were even variations between the 10 or so samples.
I dont honestly know how the magnets are mass produced or if there are certain specifications or tolerances to them and I am not about take a night course in Physics.
I mean, does the size matter, or do they just soak certain chunks of metal in the "magnetic dunk tank" longer. I will leave those questions to people that know. I am sure the guy that works at the magnet factory has a tool and a method for testing their strength. And I am pretty positive that it isnt a small screwdriver.
'lint.

 
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11-08-02, 05:50 AM   #13  
J A Boggan
Thanks for the valuable information and by-the-way do you know off-hand where I might get one of those spark testers with the pressurized chambers? I believe I could use one.

 
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11-08-02, 06:06 AM   #14  
buttlint
J. I have looked for years for a replacement, but no can find. I hope someone can answer that question, mines getting pretty ragged.

 
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11-08-02, 12:22 PM   #15  
J A Boggan
I keep looking thru my catalogs and finally found one in a Foley/Belsaw catalog. It's got a pretty good price tag, $49.99, but if it'll do what you say it may be well worth it. Their phone number is 1-800-821-3452 and the number of the tester is EGR5975479.

 
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11-09-02, 05:39 AM   #16  
buttlint
Thanks, J.A. I shall check it out.

 
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