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Thread: Mag Mystery

  1. #1

    Mag Mystery

    Have a Slick mag on one side of an O-320. EI on the other side. Mag has about
    600 hours since new and never removed for inspection yet. Plugs were new a
    couple hundred hours ago. They were cleaned and gapped under 100 hours ago.
    RPM drop at 1800 RPM runup is only about 60 RPM.

    Problem: Lately the engine almost won't run on the mag alone at low RPM and if
    low enough will just die. Of course it runs fine on the EI at low RPM. And
    runs fine with the mag at high RPM.

    Any suggestions? Pulling the mag is my next step but grounds me for as long as
    it takes to have it sent off and repaired if necessary. Just wondering about
    any other ideas. Wish I had the tools to do it myself. The Service Pro, Joe Logie, from
    Champion went over a spare I have (no impulse for it) in about 15 minutes at
    OSH.....

    Timing has not been checked yet.

  2. #2

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    Probably just bad points. You could get by with just replacing them if yr aircraft is non-certified.

  3. #3

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    Quote Originally Posted by flyingriki View Post
    The Service Pro, Joe Logie, from
    Champion went over a spare I have (no impulse for it) in about 15 minutes at
    OSH.....
    swap the impulse coupling from the one on the engine, 1 cotter key, 1 nut, and pull it.

  4. #4
    Quote Originally Posted by Tom Downey View Post
    swap the impulse coupling from the one on the engine, 1 cotter key, 1 nut, and pull it.
    Different part number. Not worth the risk without confirmation that it is compatible. Champion say no and the engine is too valuable to play around in the acc. case...

    Guess Mike was just waiting for me to watch the webinar...... will pull it and get it IRANed this week Mike!

  5. #5

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    Quote Originally Posted by flyingriki View Post
    Different part number. Not worth the risk without confirmation that it is compatible. Champion say no and the engine is too valuable to play around in the acc. case...

    Guess Mike was just waiting for me to watch the webinar...... will pull it and get it IRANed this week Mike!
    Which part number? mag or impulse coupling?

  6. #6

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    Once the engine is running the impulse coupling is no longer effective, it's only for increasing the starting spark. Fly-weights inside the coupling are forced outward by centrifugal force thus taking the spring action of the coupling out of the system. Slicks are bad about the plastic cam for the points wearing down and decreasing the point opening gap. I've also seen the electrode inside the plastic distributor gear come loose several times and cause the timing to be all over the place. 600hrs is a long time for a Slick mag without inspection. I believe a 500 hrs O/H interval is recommended. Ck your timing with the new Rite-System Kit if you want it to be digitally accurate.

  7. #7

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    Mag Mystery

    Mike Busch is really adamant about getting mags IRAN d every 500 hrs. He also stresses sending them to a specialist rather than your friendly mechanic, as there are a number of special tools required not usually present in most A&P's shops.......

  8. #8
    Quote Originally Posted by SteveC View Post
    Mike Busch is really adamant about getting mags IRAN d every 500 hrs. He also stresses sending them to a specialist rather than your friendly mechanic, as there are a number of special tools required not usually present in most A&P's shops.......
    As I said, he was probably waiting to see if I'd watch the webinar last night, and I did. So I know what he recommends. And he's right.
    But I watched the Champion Customer Service chief who writes the manuals and the ADs open my spare up, clean and inspect it, set e-gap and install a new carbon brush in about 10 minutes. All while explaining what he was doing to the folks at his booth at Oshkosh. The "special" tools are so small you could hold them all with three fingers. So it doesn't take a genius to do the Slick IRAN. And i'ts kind of a drag to see $250-$300 base charges plus parts to IRAN them. But still not worth the couple hundred dollars for the tools, at least to me since I only have one and will probably replace it with another EI next time it comes due.

  9. #9
    Mike Busch's Avatar
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    Quote Originally Posted by flyingriki View Post
    I watched the Champion Customer Service chief who writes the manuals and the ADs open my spare up, clean and inspect it, set e-gap and install a new carbon brush in about 10 minutes. All while explaining what he was doing to the folks at his booth at Oshkosh. The "special" tools are so small you could hold them all with three fingers. So it doesn't take a genius to do the Slick IRAN. And i'ts kind of a drag to see $250-$300 base charges plus parts to IRAN them.
    Yes, he does put on a very entertaining and informative show, and he does know his stuff.

    However, a proper 500-hour IRAN involves a great deal more than what he demonstrates at AirVenture. It requires a coil and bearing inspection, a good deal of lubrication at various key points inside the mag, and then putting the mag on a test stand and stress-testing it to make sure it's putting out rated voltage. So it's not quite as quick as what the Champion/Slick guy demonstrates at the booth.

    I have done many 500-hour IRANs on Bendix S-1200 mags, and I figure about 2 hours per mag to do the job right (including removal and reinstallation). There are four S-1200 mags on my Cessna twin, so doing the 500-hour IRAN on all four mags takes me a full 8-hour day. And that does not include testing (because I don't have a mag test bench). Having become older and wiser, I no longer do my own mags, I send them out to Aircraft Magneto Service up in Washington state, where Cliff Orcutt (who has been working on mags his entire adult life) does a far better job than I could do.
    Michael D. Busch A&P/IA CFIA/I/ME
    President, Savvy Aviator, Inc.
    President, Savvy Aircraft Maintenance Management, Inc.
    2008 National Aviation Maintenance Technician of the Year

  10. #10

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    Quote Originally Posted by Mike Busch View Post
    I send them out to Aircraft Magneto Service up in Washington state, where Cliff Orcutt (who has been working on mags his entire adult life) does a far better job than I could do.
    I've been working on mags all my life too, I'll open and take a look, but once the problem has been determined the mag goes away. I don't even do my own mags. I use Al at Savage mag in CA.
    here is what you usually find: bad rotor, and a bad distributor block
    DSCN2294.jpgDSCN2290.jpg

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