From my web site:
Last April I had a mag fail during a mag check on run up (466 hrs). I took it back to the hanger and did some troubleshooting. Yep it was dead. I had a brand new one on the shelf that came with the engine. I had installed an electronic ignition on one side before it was ever started. I installed it and sit the dead one on the shelf to troubleshoot further at a later date. So that time has come, I wanted to have a good spare on the shelf. I had already taken it apart and narrowed it down to either the condenser or the coil. The easiest thing to check was the condenser all I had to do was swap the cover which houses the condenser and see if the installed mag worked or not. Of course it worked just fine, which means the coil in the dead mag is the part that was dead. A new slick coil cost about $275. I decided I would try to locate one on the Van's Airforce web site. I got a suggestion to contact Aircraft Magneto Service in Washington state. I sent them an email and they told me that they do not sell used coils but suggested that I purchase a Tempest PMA coil, P/N A-13009. They said it is a more robust coil and would not fail and it is cheaper. They went on to explain to me why my coil failed, or at least most likely why it failed. They said that most coils fail due to a bad spark plug. They told me to check the ohms resistance of my plugs and if any checked over 5000 ohms to though it away and replace it. This was news to me I had never heard anything about this. I did not think I would find a bad plug, they were all firing just fine and I had just cleaned them and did not see anything wrong with them. They said to put one probe into the barrel and touch the other one to the tip. Three of them measured between 1341 and 1457. The last one I could not get a reading on at all. I told Aircraft Magneto Service what I found and they told me, that plug is what caused my coil to fail. Even though it was firing good it had a problem. I told them that I had dropped a plug the first time I installed them but I didn't find anything wrong with it and it was working just like it should. I guess I had damaged the plug but could not tell. So, I guess it all makes sense. I'm here to tell you, just like everyone says, if you drop one throw it away. A $22 plug cost me a $275 coil. I never have read anything about checking the resistance of your spark plugs, so if you never have either, now you have!
Just trying to help others avoid problems that I have had, hope this helps
Last April I had a mag fail during a mag check on run up (466 hrs). I took it back to the hanger and did some troubleshooting. Yep it was dead. I had a brand new one on the shelf that came with the engine. I had installed an electronic ignition on one side before it was ever started. I installed it and sit the dead one on the shelf to troubleshoot further at a later date. So that time has come, I wanted to have a good spare on the shelf. I had already taken it apart and narrowed it down to either the condenser or the coil. The easiest thing to check was the condenser all I had to do was swap the cover which houses the condenser and see if the installed mag worked or not. Of course it worked just fine, which means the coil in the dead mag is the part that was dead. A new slick coil cost about $275. I decided I would try to locate one on the Van's Airforce web site. I got a suggestion to contact Aircraft Magneto Service in Washington state. I sent them an email and they told me that they do not sell used coils but suggested that I purchase a Tempest PMA coil, P/N A-13009. They said it is a more robust coil and would not fail and it is cheaper. They went on to explain to me why my coil failed, or at least most likely why it failed. They said that most coils fail due to a bad spark plug. They told me to check the ohms resistance of my plugs and if any checked over 5000 ohms to though it away and replace it. This was news to me I had never heard anything about this. I did not think I would find a bad plug, they were all firing just fine and I had just cleaned them and did not see anything wrong with them. They said to put one probe into the barrel and touch the other one to the tip. Three of them measured between 1341 and 1457. The last one I could not get a reading on at all. I told Aircraft Magneto Service what I found and they told me, that plug is what caused my coil to fail. Even though it was firing good it had a problem. I told them that I had dropped a plug the first time I installed them but I didn't find anything wrong with it and it was working just like it should. I guess I had damaged the plug but could not tell. So, I guess it all makes sense. I'm here to tell you, just like everyone says, if you drop one throw it away. A $22 plug cost me a $275 coil. I never have read anything about checking the resistance of your spark plugs, so if you never have either, now you have!
Just trying to help others avoid problems that I have had, hope this helps
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