Left/Right magneto = top or bottom plug?

Discussion in 'Maintenance Bay' started by John Richardson, Jun 15, 2020.

  1. John Richardson

    John Richardson Pre-Flight

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    On a lycoming 0-540, which magneto powers the top plug on cylinder #6, and which powers the bottom plug?

    I can trace the lead, but I’m not sure which magneto is considered “left” or “right”.
     
  2. weirdjim

    weirdjim Ejection Handle Pulled

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    Which is a stupidity I've fought against for fifty years. "Port" and "Starboard" should take care of that little problem, shouldn't it? Same for "right wing" and "left wing" and all of the other "left" and "rights".

    Don't tell me there is a standard. I've looked for years and haven't found one.

    Jim
     
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  3. PaulMillner

    PaulMillner Line Up and Wait

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    1. 2. 3. 4. 5. 6.
    Top. L. R. L. R. L. R.
    Bot. R. L. R. L. R. L.

    does that help? 10% chance someone wired your backwards...

    Paul
     
  4. John Richardson

    John Richardson Pre-Flight

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    Very useful, thank you.
     
  5. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    If I recall.....the wiring harness is marked. Each lead for each mag.....
     
  6. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    I think he asked, ‘which mag is L and which is R?’.
    As in, it seems he is unsure if that means looking at the engine from the cockpit or the propeller.
    If so, it is from the cockpit.
    I am unsure about pusher a/c however.
     
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  7. Dan Thomas

    Dan Thomas Final Approach

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  8. Silvaire

    Silvaire En-Route

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    You gotta explain that one to me. The only difference between the two diagrams is that in one the top plugs use solid lines and in the other the bottom plugs use solid lines.
     
  9. Dan Thomas

    Dan Thomas Final Approach

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    Hm. Didn't catch that. Probably an error that Lycoming has never corrected.
     
  10. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    They’re opposites
     
  11. Doug Reid

    Doug Reid Pre-takeoff checklist

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    Right and left as seen from the pilot's seat. I have seen ignition wires in all sorts of configurations.
     
  12. smv

    smv Pattern Altitude

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    The dashed lines are bottom plugs, the solid lines are top plugs.
     
  13. Lindberg

    Lindberg En-Route

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    Or the bottom plugs are the dotted lines in both.
     
  14. Silvaire

    Silvaire En-Route

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    Where did you get that? It doesn’t say that anywhere in the text. There’s no legend for the figures.
     
  15. smv

    smv Pattern Altitude

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    Logic.
     
  16. Dan Thomas

    Dan Thomas Final Approach

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    And the manual itself says nothing.
     
  17. Bell206

    Bell206 En-Route

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    FWIW: It's my understanding the dotted lines and dotted lead connectors represent "hidden" items that run below the cylinders/baffling, i.e., the ignition leads to the bottom plugs. Some Lycoming books do a better job at the difference.
    As to which mag powers the top or bottom plug will depend on which routing option was selected when the ignition leads were installed. See the diagrams in Post 7. On which mag is considered the LEFT or RIGHT, here it is straight from the book...
    upload_2020-6-23_12-25-7.png
     
  18. bnt83

    bnt83 Final Approach PoA Supporter

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    Aren't the harness leads marked? I know its not a 540 manual...
    upload_2020-6-23_13-12-5.png
     
  19. Silvaire

    Silvaire En-Route

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    So what is wrong with the logic that one spark plug is above the other? They aren't side by side. Obviously they just didn't want to take the time to make a second drawing but they should have at least included a simple legend such as:

    _____ top
    ------- bottom

    Otherwise we are left having to make an assumption. You are correct however because given the choice between these two logic trees the only one that results in a solution is the one that adheres to the legend. Considering the graphics technology available at the time the Lycoming manual was printed it's likely that there probably was a legend that inadvertently got left out or cut off.
     
  20. Lindberg

    Lindberg En-Route

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    You could assume the opposite and nothing would change.
     
  21. Silvaire

    Silvaire En-Route

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    Yes, that was my point. Given the figures as they are presented with no other information the first "logic" that I would apply is that since the spark plugs are depicted vertically in the pictures then the upper one must be the top and the lower one the bottom. But using that logic there is no solution, the two diagrams are identical. So if you use the solid vs dashed line logic you end up with the two opposite configurations but you still have to make an assumption as to weather the solid or the dash equates to the top plug. Do you toss a coin?
     
  22. Lindberg

    Lindberg En-Route

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    They aren't. The solid and dashed lines are inverted.
    You don't because it doesn't matter. Whichever way you decide to read the diagrams, they give the same two options. In both drawings, no matter which set of lines is top or bottom, each mag goes to top plugs on one side and bottom plugs on the other. The second diagram is simply the reverse of however you read the first diagram.
     
  23. Silvaire

    Silvaire En-Route

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    Ahh I get what you are saying. They are two alternatives, there is no right or wrong, you can do it either way so it doesn’t matter what you think the solid or dashed lines mean.
     
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  24. tsts4

    tsts4 Cleared for Takeoff

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    FYI, if you look at the OH manual, on the pervious page to where these 540 diagrams are located they cover the 4-bangers and their diagrams much more clearly show that Lycoming uses dashed lines for the bottom ignition wires and solid lines for the top wires in their diagrams.
     
  25. bnt83

    bnt83 Final Approach PoA Supporter

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    Which mag(s) have an impulse coupling? Which cylinder(s) are primed?

    Some 4 bangers only fire half the spark plugs during start, some airplanes only prime 1 out of 4 cylinders.