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Old August 17th, 2010, 03:04 PM   #1
davmast davmast is offline
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Rough Magneto

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
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Old August 17th, 2010, 03:20 PM
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Re: Rough Magneto

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.
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Old August 17th, 2010, 03:25 PM
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Re: Rough Magneto

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.
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Old August 17th, 2010, 03:47 PM
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davmast davmast is offline
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Re: Rough Magneto

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
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Old August 17th, 2010, 03:49 PM
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Re: Rough Magneto

http://www.kellyaerospace.com/magneto_FAQ.html

http://www.sacskyranch.com/aircraft_...leshooting.htm

http://www.amtonline.com/publication...=836&pageNum=1
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Old August 17th, 2010, 03:55 PM
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Re: Rough Magneto

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Originally Posted by davmast View Post
Yes, the magneto has 500 hours as well.
Is that a Slick or Bendix mag?
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Old August 17th, 2010, 05:00 PM
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Re: Rough Magneto

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Originally Posted by Ron Levy View Post
Is that a Slick or Bendix mag?
Can't be slick, he said it is rough...
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Old August 17th, 2010, 11:41 PM
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Re: Rough Magneto

Quote:
Originally Posted by davmast View Post
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

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
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Old August 18th, 2010, 03:41 PM
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Re: Rough Magneto

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Originally Posted by Capt. Geoffrey Thorpe View Post
Can't be slick, he said it is rough...
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Old August 20th, 2010, 01:48 PM
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Re: Rough Magneto

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"That's gold, Jerry! Gold!"
Yes Ed, true any way you look at it.
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Old August 21st, 2010, 02:55 PM
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Re: Rough Magneto

I wouldn't use anything but Bendix.
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Old August 21st, 2010, 03:52 PM
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Re: Rough Magneto

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.
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Old August 21st, 2010, 08:13 PM
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Re: Rough Magneto

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Originally Posted by taters View Post
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.

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

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Old August 22nd, 2010, 05:20 PM
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Re: Rough Magneto

Quote:
Originally Posted by taters View Post
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.
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
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Old August 22nd, 2010, 07:24 PM
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Re: Rough Magneto

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Originally Posted by Dan Thomas View Post
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
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 ****.
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Old August 22nd, 2010, 08:12 PM
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Re: Rough Magneto

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Originally Posted by taters View Post
OK,

I ve had the same issue on several planes but the bonanza I fly the most has had this problem 3 times . This plane has a continental/Bendix.
-Once it was the spark plug wire grounding against the spark plug wire. Fixed it.
-Once they thought it was an induction leak, there was some fuel staining. They fixed the leak , made no difference,

-Took it back, they looked at the P-leads so see if they were causing some kind of intermittant grounding. NOPE! Was suggested I swap left/right mags with each other (leaving the harnesses in place) to know for sure if it was the mag. I think I have been misunderstood on that onw. I went ahead and had them both tested and sure enough one was worn out pretty badly. Sent them to Kelley, got them back works fine.

Being that Kelley didnt make the mag Im not to worried about it. But I can atest that the starters they sell are not worth a pitcher of warm ****.

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
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