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Old 19-08-17, 11:59 PM   #1
Robotstar5
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Default Briggs & Stratton Magneto

Yes I know it's a mere youth at 30 years old but I've got no spark on the old ride-on mower. Tried holding the HT lead a few mm from the engine while turning it over and no spark. I understand how a points driven system works, but this one has a magnet in the flywheel to induce current in the coil and I can't get my head round how it's wired. One end of the HT coil is connected to the frame with a ring terminal and the frame is bolted to the engine to complete the circuit, the bit I don't understand is a second ring terminal under the same bolt goes to a wire on the ignition switch which grounds it to stop the engine, how does grounding an already grounded wire stop the engine???

I must have my stupid head on today as there can't be a much simpler ignition system

Mag02R by Robert Starr, on Flickr

Stuart.
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Old 20-08-17, 11:48 AM   #2
keith-pu8
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An ignition coil has two copper coil windings, a primary and a secondary winding.
The primary is a thick wire and the secondary in a very thin wire, which is the wire that breaks and stops the coil working 99% of the time.
A picture of a villiers coil I did may help.
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Old 20-08-17, 11:56 AM   #3
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Keith,
Are you saying you rewound/re-manufactured a Villiers coil?

If so, please elaborate.....
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Old 20-08-17, 12:24 PM   #4
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Quote:
Originally Posted by keith-pu8 View Post
An ignition coil has two copper coil windings, a primary and a secondary winding.
The primary is a thick wire and the secondary in a very thin wire, which is the wire that breaks and stops the coil working 99% of the time.
A picture of a villiers coil I did may help.
As far as I can see/test, there is only one winding, there is no LT side as no points to switch it, it seems to work purely by induction of the magnet in the flywheel?.

Stuart.
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Old 20-08-17, 01:08 PM   #5
dannysdriver
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Default Briggs and stratton

I think you have a magnetron ignition coil which did away with the points and condenser on later briggs engine,They could also be retrofitted to older engines.
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Old 20-08-17, 02:28 PM   #6
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Yes that is a magnetron coil and if you haven't got a spark, then there are several things you can check. What is the airgap between the coil legs and the magnet in the flywheel, it should be about 25thou. do you have a spark if the stop wire isn't connected the coil, much time has been spent testing coils etc when the fault is the OPC system (oops OPC = Operator Presence Control). If the airgap is correct, the magnet in the flywheel is magnetic and there isn't a spark with the stop wire disconnected, they it sounds like you will need to airtest the coil and find a new one.
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Old 20-08-17, 03:08 PM   #7
keith-pu8
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Quote:
Are you saying you rewound/re-manufactured a Villiers coil?
No, this was just a 3D picture I did to show a Villiers coil.
I have wartime and MK1 coils on my motors, plus a hand full of spare complete ignition systems, as you do.
They do re-manufacture most if not all villiers coils, even twin spark, which I already have, but they are pricey, a long villiers wartime coil, is about 65.
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Old 20-08-17, 04:34 PM   #8
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Ahh..ok.
Thanks for the reply anyway.....65! Yeeeeouch!..
I have engines not worth that....
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Old 20-08-17, 09:00 PM   #9
Windrush
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Quote:
Originally Posted by Chippie View Post
Ahh..ok.
Thanks for the reply anyway.....65! Yeeeeouch!..
I have engines not worth that....



They wont be worth very much at all without a spark!

Pete.
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Old 20-08-17, 09:02 PM   #10
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I think 65 is a good price for a working magneto coil.

Martin P
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