Magneto test ?

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Model T Ford Forum: Forum 2012: Magneto test ?
Top of pagePrevious messageNext messageBottom of page Link to this message  By ken bechtel on Thursday, September 13, 2012 - 07:11 pm:

can a magneto be tested out of the car? thanks. Ken


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Thursday, September 13, 2012 - 07:50 pm:

The field coil ring can be tested out of the car by putting a few amps of DC through it and testing the amount of magnetism present at each coil pole. (e.g., screwdriver or hacksaw blade). Before someone jumps in and says you shouldn't put current into a magneto, note that I said 'out of the car' - where the magnets are nowhere near the coil.
The magnetic pull should be the same from each coil.
A more elegant way is to feed the coil ring with AC and then test the induced voltage from a solenoid held against each coil pole in turn. This would show up any shorted turns within each coil.
If one starts from the coil connected to the magneto post and works around to the last one, any loss of magnetism along the way indicates a breakdown to the coil plate.


Top of pagePrevious messageNext messageBottom of page Link to this message  By ken bechtel on Thursday, September 13, 2012 - 08:35 pm:

thanks John! i just put 2 amps to the mag and laid a hacksaw blade close to each post and it pulled the blade tight against and i could feel the magnetism in the blade


Top of pagePrevious messageNext messageBottom of page Link to this message  By ken bechtel on Thursday, September 13, 2012 - 08:38 pm:

one more question, is it safe to use a spray brake cleaner to the mag coils? thanks. Ken


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Friday, September 14, 2012 - 09:11 am:

Ken
I think I can sense where your going with that last question?
If your planning upon cleaning and reusing an used field ring, I recommend not doing so.
No matter what you do you will never get it clean enough to properly re-coat. The problem is the cotton tape used on the individual windings is rotten and when it dries out it will simply fall off or abrade away in the sloshing oil.
If it fails it is not like changing a spark plug to correct.
I recommend you spend the money, obtain and install a quality rebuilt unit.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell on Friday, September 14, 2012 - 09:34 am:

Ken,

Listen to Ron, here is a photo of what someone did with my coil ring. Looks like it was cleaned then re-coated. Needless to say, the magneto didn't work.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mack Cole ---- Earth on Friday, September 14, 2012 - 09:33 pm:

T's are a funny thing.
When I assembled my engine in my TT old Algores internet was young and I had no access to it.Just a couple books and the knowledge of the fellow that sold me the rusty frame.
When it came time to assemble a mag coil it came to pick the best 1 out of a dozen,rinse it off with some solvent,cant remember what,and coat the bare spots with indian head gasket cement.So that is what happened.I have had that engine running since 96 and the mag did not work.Until a couple weeks ago.
I decided there was nothing to loose by chargeing the magnets.It ran.Ok but the longer I use it,the better it runs.I didnt and still dont believe it.
As the old saying goes,your mileage may vary.
What Ron and others are telling you is the truth.Useally a cleaned and patched coil will get your car finished,and leave you needing to take it apart again in a few months.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, September 15, 2012 - 01:23 pm:

The original windings had a cloth tape around them. As you can see in the picture, the very closest coil to the camera has the tape chipped away and the bare copper was painted with the red stuff. All that tape on all the coils is in the same condition. Very fragile. It just hasn't chipped off yet. It is time to rewind the coils using new tape. The book Electrical System had details on how to do it with fiberglass tape and resin. I have rewound two coils and found them to work very well. You can also purchase a rewound coil from any of the vendors. Even if you get a used coil to test "good" there is no way of telling how it will perform once in the car, and the labor cost to pull the engine and transmission to replace it later will be far more than the price of a rewound one.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By ken bechtel on Sunday, September 16, 2012 - 03:12 pm:

The windings look fine but they are old. I was only asking about brake cleaner to get the years of oil off of them. I fully understand that nothing sticks to anything that is saturated with oil. What makes a mag stop working? I have read that flying debris will do it and also a loose solder connection.Does the windings burn out or is it a ground out problem when the insulation breaks away? thanks all. Ken


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Sunday, September 16, 2012 - 06:05 pm:

Several things which will make a magneto stop working: open winding or solder connection. Shorted windings. Grounded windings grounded to core somewhere on the magneto. Magnets lost magnetism (discharged). Magnets too far from the magneto coil due to wear on the rear main bearing. Magneto contact not making good connection with the winding. Magneto contact grounded. Bad wire between magneto contact and switch. Bad switch.

Any attempt to clean the windings will just make it more likely to destroy the insulation. The original insulation is so fragile even a touch can destroy it. If you want a good magneto first check the wear on the rear main bearing, second replace with rewound coil, third recharge the magnets (check for broken magnets while doing) fourth set the clearance between magnets and ring to no less than 25 thousandths and no more than 40 thousandths. The closer to 25 the better because wear on the rear main bearing will increase the clearance. Make this adjustment with the engine nose down and supported in such a way that the flywheel hangs. That way you will make the adjustment while the magnets are in their closest possible distance from the coils.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By ken bechtel on Sunday, September 16, 2012 - 07:36 pm:

Norman,Thanks for all the good information. I am in the process of a total rebuild. not just a clean it up and see what happens. new bearings,rods,pistons,timing gears,cam bearings... I am new to the model t so i am trying to address everything so hopefully when the engine is in the car it can stay there for a few years.lord knows i`ll be a nerves wreck when the time comes to try it`s first start up. thanks again. Ken


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Sunday, September 16, 2012 - 10:55 pm:

I've had some success with a mag coil by taking it to my friendly local electric motor rewinder. He will dip the whole assembly in varnish and bake it with his other motor rewinds.

Don't blast it with compressed air or a solvent gun, just wash gently in your choice of solvent to try and get most of the oil off. A thin smear of grease will prevent the varnish sticking to the poles, mounting points and contact.

Test it after baking.

cheers

A


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