Rough Magneto

Discussion in 'Maintenance Bay' started by davmast, Aug 17, 2010.

  1. davmast

    davmast Filing Flight Plan

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    Hey everyone, recently I've been having trouble with my right mag. I have a PA-18 with a O-320 160 hp with 500 hours. I am getting a rough right mag during the run up mag check, the left and both are good. The right mag only drops 125 rpms but it is rough when I check it. This only seems to happen on the first flight of the day and mag checks in the air are fine. Is this an indication of my mag going bad or is it a differet issue? I actually just had a stuck exhaust valve so all of the cylinders were taken off and the valves were reamed. Any help would be appreciated.

    Thanks,

    Dave
     
  2. tonycondon

    tonycondon Gastons CRO (Chief Dinner Reservation Officer)

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    does the mag also have 500 hrs on it? I think that is a recommended interval to have them inspected. might not be a bad idea to make sure everything is still looking OK.
     
  3. poadeleted20

    poadeleted20 Deleted

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    Slick mags have a recommended 500 hour inspection, as well as replacement of some internal parts. However, I'd start by looking at the plugs for wear/gap/lead/etc -- lot easier than checking mags, and often the cause of such issues.
     
  4. davmast

    davmast Filing Flight Plan

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    Yes, the magneto has 500 hours as well. Plugs are good, they are brand new, pulled them and they're burning perfectly. I guess the answer is to have the mags inspected. Thanks for the help.

    Dave
     
  5. Steve

    Steve En-Route

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  6. poadeleted20

    poadeleted20 Deleted

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    Is that a Slick or Bendix mag?
     
  7. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Final Approach

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    Can't be slick, he said it is rough...
     
  8. Dan Thomas

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    Roughness could be an induction leak leaning once cylinder enough to cause roughness on one mag. Run up, switch to that mag, and lean to see what it does.

    Some engines can suck enough oil at idle to fill the bottom plugs with oil and make them misfire on the runup. The small Continentals are famous for that, but a Lyc might do it, too. It would only take one cylinder to do it. To prove it, run up to full power for five seconds or so, back to runup RPM, and try that mag again. The high power will usually clear any oil from a drowned plug.

    Dan
     
  9. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    "That's gold, Jerry! Gold!"
     
  10. B2Soar

    B2Soar Pre-takeoff checklist

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    Yes Ed, true any way you look at it.:crazy:
     
  11. Tim

    Tim Line Up and Wait

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    I wouldn't use anything but Bendix.
     
  12. taters

    taters Pattern Altitude

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    I just went through this...first flight of day rough mag in Bonanza .after about 5 min it was fine..in my case it was the mag. got it overhauled and now every thing is fine.

    If you dont have any blue stains on your cylinders then there is no fuel induction leak. You might also check your P-leads and spark plug lead wires (heilo-coils) but Im sure its the mag...if you need to be sure switch the mags and the problem should "travel" to the other side..Kelley Aerospace can fix them for pretty cheap.
     
  13. weirdjim

    weirdjim En-Route

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    A prize for the person who finds the most untruths and errors in this post.

    Jim
     
  14. Dan Thomas

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    An induction leak lets air in; it doesn't necessarily let fuel out.

    Heli-coils are the steel threaded inserts in the sparkplug hole in the aluminum head. They have nothing to do with plug leads.

    On the Lycoming the right mag fire the top plugs on the left side and the bottom plugs on the right, and the left mag fires the bottom left plugs and top right plugs. The left mag does not fire just the left plugs and so on.

    Kelly doesn't rebuild Slick mags. And if they did it would be neither cheap nor reliable. We've had considerable trouble with some of their stuff lately.

    Dan
     
  15. taters

    taters Pattern Altitude

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    First my setup was continental/bendix
    -What I was referring to was physically moving the mags leaving the harness in place as a poor mans way of seeing if there was a problem with the mag.

    -I have had a plug coil ground against the sidewall of a spark plug and cause a rough mag that got better after a while. I am wrong about calling that part a helo-coil.

    -Didnt really pay attention to the fact that a slick is the mag we are talking about but also didnt know Kelly doesnt deal with them. Pretty much every Slick mag Ive had go bad had to be replaced.

    - I havent had an issue with the re-biult mag....but the starters they sell arent worth a pitcher of warm ****.
     
  16. Dan Thomas

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    On the Lycoming the impulse mag is on the left and has a deeper gear offset than the right, so they can't be switched left for right unless the adapter is moved as well.

    We've had trouble with Kelly's rebuilt starters. They stick a decal on the starter warning you to use only dry silicone lube on the starter drive, never oil, and when they start sticking we open them and find grease on the drive. Grease attracts dust and makes a sticky sludge, and of course dry silicone lube can't do anything if grease is present. Bunch of junk.

    Several failed Kelly alternators, too, with far too much grease in the rear bearing that flies around in there and gets onto the brushes and slip rings and makes the field circuit resistance go out of sight, and the output falls off to nothing useful.

    Had several Kelly electronic voltage regulators that lasted a very few hours. Those components, of course, are not returnable under any circumstances.

    Dan