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Thread: Bendix magneto internal timing ??

  1. #1
    Gilbert Pierce's Avatar
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    Default Bendix magneto internal timing ??

    My Vag with the Continental A65 has been getting hard to start. During the annual timing check I found the Left Bendix magneto, S4RN21 with impulse coupling, to be slightly retarded. I got the mag back in time but had to pull it and move it a tooth to do so. Suspecting at this point my hard starting problem might be caused by slipped internal timing I pulled the rubber plug in the top of both mags. The right mag's red tooth was aligned with the center of the viewing hole on top of mag. The left Mag's red tooth was not visible so I pulled the magneto off for further inspection.

    Bendix S-20 & S-200 series Overhaul and Parts Magneto Manual dated May 1989 gives the method for internal timing which basically says to line up the red timing mark in the middle of the window, turn the mag backwards until you get it on the magnets neutral position. Then you install the timing tool, which I have access to but have not used as it is 5-00 miles away, set it at zero, turn the mag in the normal direction 10 degrees on the pointer and at that point the contact points should just start to open. I estimated what ten degrees would be by counting the number teeth on the gear etc etc and determined when close to proper internal timing the red timing mark is still not visible in the window.

    When the internal timing is correct should the Red tooth on magnet gear be centered in the window as the right mag is? Several unofficial publications I have read say it should. If so I need to delve deeper into the mag and see what is going on. Slick magneto's I understand and internal timing is easy. Bendix is a different animal to me at this point.

  2. #2

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    Default Re: Bendux magneto internal timing ??

    I had a TriPacer years ago with S-20 mags. One mag would go out of timing every so often, and I'd pull it, split the case ad realign the gears correctly. After about 3 times, I realized the bushing that holds the rotor was worn enough to let the rotor gear disengage from the magnet gear. Got the mag overhauled and all was well.

  3. #3

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    Default Re: Bendux magneto internal timing ??

    Ted, Velocity Magneto El Reno, Oklahoma 405 413 4972 call or text

  4. #4
    pa20's Avatar
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    Default Re: Bendux magneto internal timing ??

    Gilbert,
    Start by setting point clearance. Then, set e-gap by adjusting the cam. Reassemble by referencing chamfered tooth to the correct position based on CCW vs CW for your installation. The red tooth on the distributor gear should be visible in the vent window. Would rather work on Bendix in lieu of Slick any day!
    Mark Ohlau
    PA-20 N7744K 2021 Donation Paid

  5. #5

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    Default Re: Bendux magneto internal timing ??

    I did a 500 hours inspection to the Bendix mag of my Cherokee last year during the annual and it worked perfectly.
    I followed the instruction manual exactly as written.
    Sorry but you really need to use the timing tools to do the job properly.

    Good luck,

    Rick

  6. #6
    Gilbert Pierce's Avatar
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    Default Re: Bendix magneto internal timing ??

    Todd I did what you suggested in your deleted post. It fixed the problem. I believe the the magnetic rotor gear was one tooth off from the white nylon gear.
    Thanks.

  7. #7

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    Default Re: Bendix magneto internal timing ??

    Quote Originally Posted by Gilbert Pierce View Post
    Todd I did what you suggested in your deleted post. It fixed the problem. I believe the the magnetic rotor gear was one tooth off from the white nylon gear.
    Thanks.
    Gilbert, see my post about the gear slipping with a warn bushing. If it slips again, thatís likely the problem.


    Sent from my iPad using Tapatalk

  8. #8
    Gilbert Pierce's Avatar
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    Default Re: Bendix magneto internal timing ??

    dgapilot
    After your slipping gear reply I disassembled the mag case and did an in-depth inspection. Everything looks good. The airplane sat for a couple of years while I replaced some remaining cotton fabric. After that there was no spark on the left mag. I disassembled it, burnished the points and put it back and it started but has been hard to start since. I think I probably assembled it a tooth off. I now have greatly furthered my education on Bendix mags. The Bendix mag tools are on there way here so I can do this properly.
    Any day you don’t learn something new is a wasted day in my opinion.
    Last edited by Gilbert Pierce; 04-30-2021 at 09:37 AM.

  9. #9
    Gilbert Pierce's Avatar
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    Default Re: Bendix magneto internal timing ??

    Setting the EGap internal timing properly works wonders. The Vag now starts cold on the second blade and hot the first. I can now prop it from behind.
    Attached Images Attached Images
    Last edited by Gilbert Pierce; 05-07-2021 at 07:50 PM.

  10. #10
    Administrator Steve Pierce's Avatar
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    Default Re: Bendix magneto internal timing ??

    Sorry the needle fell out on my tool box while I was wrapping everything up to ship. Looks like you adapted and overcame.
    PXL_20210501_195503906.jpg

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