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Thread: Mag Mystery

  1. #11

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    Mike, what would you think a IRAN on a Slick 4 cylinder mag will cost with a bad distributor block, bad rotor, bad condenser, bad points, with the labor to pull and replace?

  2. #12
    Mike Busch's Avatar
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    Quote Originally Posted by Tom Downey View Post
    Mike, what would you think a IRAN on a Slick 4 cylinder mag will cost with a bad distributor block, bad rotor, bad condenser, bad points, with the labor to pull and replace?
    Too much.

    The best mag specialty shops (like Aircraft Magneto Service or G&N Aircraft) will let you know right away if your mag is uneconomical to IRAN, and typically won't charge you anything other than freight to send the mag back to you so you can use it as a core in exchange for a rebuilt mag. This doesn't happen too often in my experience, but it does sometimes. A cracked case or a damaged rotor will typically render the mag uneconomical to repair.

    Points, felts and carbon brushes are almost always replaced at IRAN. Ditto with cam on Slick (but not Bendix). Condenser is usually good for at least 5 years. Block sometimes has to be replaced, usually not. Same with the coil assembly, bearings, oil slinger. Slicks are less robust but also considerably cheaper. The Bendix S-1200s I use on my airplane are extremely robust but also quite pricey (and heavy).

    We usually figure one hour per mag to remove, pack and ship, re-install and re-time. We typically ship 2-day each way, and figure 2-3 days turn time at the mag shop, so total elapsed time is about one week. If we pull the mags on the first day of an annual inspection (right after the hot compression test), the mags will get back in time not to hold things up.
    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

  3. #13

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    When you use new mags at overhaul they are designed to go to TBO with minor maintenance. when you do the mag IRAN at 500 hours, it does not require many internal parts, shipping and labor to get $600 involved, do the math it is more economical to run until you have a high mag drop then replace the slick with a new from AS&S at $800 +-

  4. #14

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    Mag problems at low RPM's is usually caused by the point gap closing to a bare minimum. This is caused by the fiber points bar on the points that follow the distributor cam action. If the cam gets dry, dirty, etc. it will wear down the rubbing bar. The results are the slow closure of the points gap. At high RM's this closure is less noticible due to other forces working on the points and electrical spark generating system. However, that RPM range will soon have problems also.
    Rule of thumb....check the mag points and gap at every 50 -100 hrs. After the points are checked or re-set, the timing should be checked too......

  5. #15

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    Quote Originally Posted by skywagon View Post
    Mag problems at low RPM's is usually caused by the point gap closing to a bare minimum. This is caused by the fiber points bar on the points that follow the distributor cam action. If the cam gets dry, dirty, etc. it will wear down the rubbing bar. The results are the slow closure of the points gap. At high RM's this closure is less noticible due to other forces working on the points and electrical spark generating system. However, that RPM range will soon have problems also.
    Rule of thumb....check the mag points and gap at every 50 -100 hrs. After the points are checked or re-set, the timing should be checked too......
    The wearing of the cam, or the cam follower will cause the points to open late, and close early, which changes the dwell of the coil induction and results in a weak spark. and of course a large mag drop.

  6. #16
    Mike Switzer's Avatar
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    For an experimental, I'd recommend taking the mag to your local tractor dealer, if they have a mechanic over 40 that knows what it is...

    Not that I ever get mine serviced, I've got an Allis Chalmers WD45, a Case SC & a Farmall M, all with mags real similar (or the same) to the ones on our "modern" planes, I never have to do anything to them. I've been mowing with the M for over 10 years with no service to the mags other than a few drops of 3 in one oil in the cups every now & then...

  7. #17

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    Hi Mike,

    I’ve got a Lycoming IO-360-A1B6 attached to a single engine airplane that is about to undergo an owner-assisted annual inspection. The engine has Slick magnetos that were installed new during engine overhaul 10 years and 490 hours ago (time for IRAN). I’ve looked at the Lycoming TCDS and see that I could switch to the TCM-1200 series provided they don’t interfere with my existing accessories or the cowling.

    One question: Provided that my Slick magnetos return from IRAN only needing points, capacitor, brush and cam, would you consider it economical to continue running the slicks if we assume that I will keep this aircraft/engine for 20+ years?
    Or do you feel strongly that the 1200 series Bendix is a much superior product in terms of reliability that you would recommend replacing the slicks sooner even if they are in a serviceable condition? It appears that the Bendix magnetos are about $1200 a piece.


    Also, while perusing the TCDS (1E10), it reads that the timing on my engine should be 25 degrees BTC with an “optional” timing of 20 BTC….hmmm…
    The engine data plate only indicates 20 degrees.
    Which one takes precedence?
    Provided that 25 degrees BTC gives adequate detonation margins, do you know what kind of horsepower increase one could expect at full power with the 5 degree advance in timing, provided that I could keep the CHT’s in check with adequate cooling?

    Thanks!

    -Drew

  8. #18
    Mike Switzer's Avatar
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    Quote Originally Posted by Mike Switzer View Post
    For an experimental, I'd recommend taking the mag to your local tractor dealer, if they have a mechanic over 40 that knows what it is...
    OK, since Riki took exception to this & called me out on it in another thread - The same magnetos we use on our aircraft engines were originally used on tractors. For an experimental you don't have to spend X AMU's to get your mag rebuilt if you have a good local tractor mechanic that has rebuilt thousands of them in his lifetime. They use the exact same parts.

  9. #19
    Thanks Mr. Busch. As you can imagine, I'll be taking your advice over that of taking my mag to John Deer. Unfortunately the moderators find that advice "valuable"....
    Sorry you have to compete with this kind of nonsense. But keep up the good work, please!

    Hal, for crying out loud, do you mean to invite a fabulous contributor like this and then encourage ridiculous input from wackos to contradict him?
    It's time to get your priorities in order. Or is this part of the 'New" EAA that wants to be everything to everybody and to heck with those that really know what they are talking about?
    Last edited by flyingriki; 01-21-2012 at 12:46 AM.

  10. #20

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    Would you allow us to know the total bill, to have your mag IRANed ?

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