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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

International H Mag


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  #1  
Old 09-29-2018, 04:29:53 PM
Steam Pig Steam Pig is offline
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Default International H Mag

Ok, having fits here. But I think I have answered my own question...
Replacing components in an H1 mag due to running /starting issues. Found what looked to be original coil and condensor. Mag still had spark at plug but erratic.
Had replacements installed and lost all spark. It appeared that the connector on the condenser (not the case) was grounded all the time so naturally I thought I messed up somewhere. Removed the coil and tested with a VOM. This is what I found. To me, that is the same as continually grounding the kill button, yes? And therefore a bad coil right out of the box...yes?
With the coil removed and all else connected as usual the points are grounded only when closed. The second pic tells me there Is a short to ground somewhere internally, right?
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  #2  
Old 09-29-2018, 06:59:50 PM
Kirk Taylor Kirk Taylor is offline
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Default Re: International H mag

Quote:
Originally Posted by Steam Pig View Post
Ok, having fits here. But I think I have answered my own question...
Replacing components in an H1 mag due to running /starting issues. Found what looked to be original coil and condensor. Mag still had spark at plug but erratic.
Had replacements installed and lost all spark. It appeared that the connector on the condenser (not the case) was grounded all the time so naturally I thought I messed up somewhere. Removed the coil and tested with a VOM. This is what I found. To me, that is the same as continually grounding the kill button, yes? And therefore a bad coil right out of the box...yes?
With the coil removed and all else connected as usual the points are grounded only when closed. The second pic tells me there Is a short to ground somewhere internally, right?
It looks like you are using the same scale on your ohmmeter to measure the primary as you used to measure the secondary. You need to change the scale to the lowest setting to read the primary resistance. The resistance is only a few ohms.
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Old 09-30-2018, 09:41:15 AM
mmcdonald mmcdonald is offline
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Default Re: International H Mag

A typical magneto coil is made of two windings/coils of wire. On the primary coil of wire one end is connected to ground the and other end of the wire is connected to the points. On the secondary coil of wire(wound on top of the primary) one end is connected to ground and the other end is the leadout/button/tab for the cap. On most coils the ground for the primary and secondary is connected and that is grounded at one place(the flat metal tab on your coil. Therefore you will have continuity from all three electrical connections. The amount of resistance(ohms) between the connections is different because of the number of turns of wire varying in the primary and secondary winding(as expressed by Kirk). Anytime you try to check most anything on the magneto with the coil connected you will typically get some amount of continuity/ohms reading. You can check to see if a winding is broken on a coil(or you can see if the resistance reading is way off) with an ohm meter but most of the time a "bad" coil is from insulation failure between the windings of wire and not a broken wire. Don't get me wrong it can happen but the only way to verify a coil is with an actual coil tester or in an otherwise functioning magneto assembly. Hope this helps.
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Old 09-30-2018, 10:42:38 AM
radiodoc radiodoc is offline
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Default Re: International H Mag

Since he has the coil out he can use some clip leads and a 9 volt transistor battery and a good spark plug to test the coil. Clip the end of two clip leads to the coil's iron core (*there may be a separate ground wire so clip that instead of the iron core). Clip another to the wire that goes to the points. Attach another clip lead to the high tension button (may have to use a bit of tape to hold it there). Clip one of the leads from the iron core (or ground wire) to the shell of the spark plug. The other lead from the core (or the ground wire) to one terminal on the battery. Connect the clip lead from the high tension button to the other connection on the spark plug. Momentarily touch the clip lead from the points wire to the other terminal of the battery. There should be a spark across the plug. If there is a spark, then the coil is probably ok. Allie
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Old 09-30-2018, 04:19:23 PM
mmcdonald mmcdonald is offline
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Default Re: International H Mag

and another thing.........If you try to test for spark with your coil the core must be installed. I have not tried the 9V battery test as described. While it may tell you if a coil is completely shot or not(no spark = completely bad?), it doesn't sound like a reliable test to guarantee a good coil. To say a coil is good, it has to be stressed in a working environment either with an actual tester or in a functioning unit. Many coil failures are related to internal heating of the coil in operation resulting in insulation failure. Also a coils spark should consistently jump at least a 3/16" air gap(most coil testers instructions I've seen specify 5 mm gap as a minimum, don't ask me why) at atmospheric pressure. I typically do not like to let one go out if it will not jump at least 1/4" on the test bench. Some well built mags will go twice that or better. Just because it will jump a 0.025" spark plug gap does not mean it will function in the combustion chamber.
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Old 10-01-2018, 02:01:05 AM
cobbadog cobbadog is offline
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Default Re: International H Mag

I will have to buy a 'pink' multi meter so my mates wont want to borrow it and not return it!
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