Bad Left Mag? Transport Options?

itsjames2011

itsjames2011

Pre-takeoff checklist
Joined
Jul 21, 2014
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165
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Chicopee MA
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Display name:
James
My Cherokee has a Lycoming 0–320-D2A 160 horse motor. During the initial mag check, both runs a tad bit sloppy, the right mag runs nice and smooth and the left Mag shows A 200-400 RPM loss, the engine runs really rough, and there is a lot of vibration and shaking. I pulled all the plugs, checked for any signs of fouling, and even checked all the plugs with a multimeter and all seems well.

The closest repair shop is about a 30 nautical mile flight from my home base. Should I just fly down on the right Mag or should I try and remove the mag and bring it down in the car? Any insight on how hard it is to take out?

James
 
Did you try and burn off the deposits on the plugs with a high power, leaned out engine run?
 
Do you have a JPI or similar engine analyzer?

What does it show during the run up on each mag? Have you tired to burn them off like Ted said?
 
Cpt_Kirk said:
Did you try and burn off the deposits on the plugs with a high power, leaned out engine run?
Click to expand...

Indeed I did more than once. I even torch cleaned it the ones that looked somewhat fouled when I pulled the plugs.
 
James331 said:
Do you have a JPI or similar engine analyzer?

What does it show during the run up on each mag? Have you tired to burn them off like Ted said?
Click to expand...

I wish. This is an old 1964 Cherokee cruiser.
50 RPM drop on the right and 200 to 400 RPM dropwhile running rough on the left.
 
itsjames2011 said:
My Cherokee has a Lycoming 0–320-D2A 160 horse motor. During the initial mag check, both runs a tad bit sloppy, the right mag runs nice and smooth and the left Mag shows A 200-400 RPM loss, the engine runs really rough, and there is a lot of vibration and shaking. I pulled all the plugs, checked for any signs of fouling, and even checked all the plugs with a multimeter and all seems well.

The closest repair shop is about a 30 nautical mile flight from my home base. Should I just fly down on the right Mag or should I try and remove the mag and bring it down in the car? Any insight on how hard it is to take out?

James
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My A&P is about the same distance away. He gave me a place to send the Mag to and have it rebuilt. I called him when it came back and he drove down and installed it. It was diagnosed by another shop because one of my partners contacted them. Their suggested repair was to buy a new Mag and install it at about twice the cost I ended up paying.
 
Okay, first things first. You're not an A&P...I can tell. Don't take offense, I don't mean any. Don't do any major repairs to your engine unless you're supervised by an A&P. I'm not trying to lecture you, but removing/replacing/timing a magneto is beyond the scope of "preventative maintenance and repairs" allowed to a pilot/owner.

Do not fly the airplane on one mag anywhere. You know it's not safe, don't even try.

I would call that A&P shop that is 30 miles away and tell them the situation. Maybe they can fly a mech to you, or give you a few things to check while you're on the phone with them.
 
S Joslin said:
Okay, first things first. You're not an A&P...I can tell. Don't take offense, I don't mean any. Don't do any major repairs to your engine unless you're supervised by an A&P. I'm not trying to lecture you, but removing/replacing/timing a magneto is beyond the scope of "preventative maintenance and repairs" allowed to a pilot/owner.

Do not fly the airplane on one mag anywhere. You know it's not safe, don't even try.

I would call that A&P shop that is 30 miles away and tell them the situation. Maybe they can fly a mech to you, or give you a few things to check while you're on the phone with them.
Click to expand...


First off I only inquired about removal of the magneto. One does not need to be in the A&P to remove anything. At no point did I ever suggest I would reinstall it :)

I have already called the A&P and he was the one who suggested that I fly down on one mag and he would diagnose and rebuild it on site. It seems public opinion is 50-50 on flying the airplane down on the right mag.
 
itsjames2011 said:
I wish. This is an old 1964 Cherokee cruiser.
50 RPM drop on the right and 200 to 400 RPM dropwhile running rough on the left.
Click to expand...

Meh

I had the same thing happen right after I bought my current plane, on the JPI I didn't show a individual cylinder with low EGTs, all was uniform, couldn't burn it off, turned out one of my slick mags was checking out on me, I ended up replacing both slicks with bendix mags.

I'm not a A&P, I haven't seen your plane, didn't even stay in a holiday inn, but from what you said I wouldn't be surprised if one mag is needing a overhaul (bendix) or replacement (slick).
 
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James331 said:
Meh

I had the same thing happen right after I bought my current plane, on the JPI I didn't show a individual cylinder with low EGTs, all was uniform, couldn't burn it off, turned out one of my slick mags was checking out on me, I ended up replacing both slicks with bendix mags.

I'm not a A&P, I haven't seen your plane, didn't even stay in a holiday inn, but from what you said I wouldn't be surprised if one mag is needing a overhaul (bendix) or replacement (slick).
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It is a Bendix mag and the mechanic on the phone Had the same conclusion. Apparently he overhauls them right at the shop.
 
itsjames2011 said:
It is a Bendix mag and the mechanic on the phone Had the same conclusion. Apparently he overhauls them right at the shop.
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At least it's not a slick.

itsjames2011 said:
First off I only inquired about removal of the magneto. One does not need to be in the A&P to remove anything. At no point did I ever suggest I would reinstall it :)

I have already called the A&P and he was the one who suggested that I fly down on one mag and he would diagnose and rebuild it on site. It seems public opinion is 50-50 on flying the airplane down on the right mag.
Click to expand...

If someone recommends you fly it down, don't listen to them and I would seriously question any work they would do, if you decide you want to fly it that's a sketchy choice YOU make, I couldn't imagine a AP is recommending you fly a sick plane, no bueno.
 
It seems public opinion is 50-50 on flying the airplane down on the right mag.
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May I respectfully tip the scales in favor of not flying it?
It is unairworthy, you've posted publicly, and there is that old 'Murphy' issue.
 
Let'sgoflying! said:
May I respectfully tip the scales in favor of not flying it?
It is unairworthy, you've posted publicly, and there is that old 'Murphy' issue.
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I honestly don't plan on it and if I did it wouldn't be without the appropriate ferry permit.
 
I would bet that the mag hasn't been off for a long time, and that the other mag was last opened up at the same time this one was.

Therefore, when one mag is bad, the other isn't likely far behind. Not the best scenario for flying on one mag to the shop.

I am constantly amazed at the magnetos I come across that haven't been inspected internally for ages. Got an airplane right now that has mags that have been on the engine for at least 1300 hours and possibly 1600 hours, and 23 years. A perfect recipe for being way beyond economical repair, not to mention rather risky. The previous owner saved a little money and the new owner might be out a lot.
 
Before I'd do anything I'd do proper trouble shooting. it may be as simple as a bad plug.

But lets just shoot the parts gun at it because some poster says so and see which works best.
 
Tom-D said:
Before I'd do anything I'd do proper trouble shooting. it may be as simple as a bad plug.

But lets just shoot the parts gun at it because some poster says so and see which works best.
Click to expand...

That's what I was thinking, a plug that looks fine may not be.
 
itsjames2011 said:
It seems public opinion is 50-50 on flying the airplane down on the right mag.
Click to expand...

Let me put my proverbial thumb on the proverbial scale as well.

Ask yourself, "What is the most conservative action?"

Then imagine the NTSB report that would have, as a contributing cause, "Operating with a known deficiency".

Links in a chain, and all that.

Don't fly with a bad mag.
 
Tom-D said:
Before I'd do anything I'd do proper trouble shooting. it may be as simple as a bad plug.

But lets just shoot the parts gun at it because some poster says so and see which works best.
Click to expand...

Intelligent troubleshooting of an issue like this often requires little more than a look at the airplane's logs. If those mags have 1500 hours on them...
 
itsjames2011 said:
My Cherokee has a Lycoming 0–320-D2A 160 horse motor. During the initial mag check, both runs a tad bit sloppy, the right mag runs nice and smooth and the left Mag shows A 200-400 RPM loss, the engine runs really rough, and there is a lot of vibration and shaking. I pulled all the plugs, checked for any signs of fouling, and even checked all the plugs with a multimeter and all seems well.

The closest repair shop is about a 30 nautical mile flight from my home base. Should I just fly down on the right Mag or should I try and remove the mag and bring it down in the car? Any insight on how hard it is to take out?

James
Click to expand...

Don't think anyone will tell you to fly it, there's a couple performance issues involved as well that can lead to you trashing your engine potentially, so all in all not worth the risk. Removal is simple, unscrew the harness cap and remove. Pull the base clamp nuts and clamps setting them aside, pull the mags and any rubber drive buffers and inspect them for condition and store them with the clamps, nuts, and screws. Do what you want with the mags, then reinstall as per the installation and timing instructions.
 
you aren't close to doing anything with the mag. First you need to rule out a bad plug and then a bad harness. Step 1 is to take all 4 plugs currently on the other mag and move them to the "bad" mag. If no change then it's on to checking the harness.
 
I wouldn’t fly the aircraft if it won't pass a magneto check.
As has already been pointed out if one magneto is failing the other is likely not far behind.
I would have a closer look at things before I assumed a magneto needs to be rebuilt.
It would probably be best to rebuild them both if one needs to be rebuilt.
I fly an experimental with a Lycoming IO-320 B1A and rebuild the magnetos every 500 hours of flight time.
Rebuilding the magnetos involves more than just replacing the points and condenser and is probably best carried out by a specialist.
 
JHW said:
you aren't close to doing anything with the mag. First you need to rule out a bad plug and then a bad harness. Step 1 is to take all 4 plugs currently on the other mag and move them to the "bad" mag. If no change then it's on to checking the harness.
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:yeahthat:

Exactly what I would do.
 
itsjames2011 said:
First off I only inquired about removal of the magneto. One does not need to be in the A&P to remove anything. At no point did I ever suggest I would reinstall it :)
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Sorry, I wasn't implying that you couldn't actually R&R the mag. It's certainly not overly complicated. It's just the circumstances involved if you were to do it and had an "issue" while flying. The FAA/NTSB would tear you a new one...
 
So I swaped all of the plugs from one mag to the other today. Top left went to top right and bottom left went to bottom right. When I went to do the run up, the left was nice and smooth and I expected the right to be terrible. Oddly enough, the engine ran smooth on L,R, and Both. Rpm drop was about 50 on each. I'm going to try to get it up in the pattern tomorrow and see how it is. It will be one of those days I'm happy I have a 13000 foot runway. Any thoughts?
 
The act of swapping either dislodged a whisker of carbon, or corrected marginal contact on an ignition lead?

You did inspect the plugs while swapping, right?
 
like he said, you either dislodges something from one of the plugs or re-positioned a shorted harness. if it's the harness it'll come back but you are on the right track. Run it awhile and see what happens. And remember to always check the cheap & easy things first. In this case, in order it's plugs, mag grounding wire, harness, mag points&condensor, and last of all sending off a mag.
 
itsjames2011 said:
So I swaped all of the plugs from one mag to the other today. Top left went to top right and bottom left went to bottom right. When I went to do the run up, the left was nice and smooth and I expected the right to be terrible. Oddly enough, the engine ran smooth on L,R, and Both. Rpm drop was about 50 on each. I'm going to try to get it up in the pattern tomorrow and see how it is. It will be one of those days I'm happy I have a 13000 foot runway. Any thoughts?
Click to expand...

Yep, you may have a plug wire going bad the was interfering with another plug wire (or grounding direct) causing the poor running. When you did the plug swap and jostled all the cables around you cleared the interference. I would give a close inspection on the wires.
 
itsjames2011 said:
So I swaped all of the plugs from one mag to the other today. Top left went to top right and bottom left went to bottom right. When I went to do the run up, the left was nice and smooth and I expected the right to be terrible. Oddly enough, the engine ran smooth on L,R, and Both. Rpm drop was about 50 on each. I'm going to try to get it up in the pattern tomorrow and see how it is. It will be one of those days I'm happy I have a 13000 foot runway. Any thoughts?
Click to expand...

Warm it up good on the ground. I had a coil fail when hot. The engine would run fine until it got up to normal operating temperature.
 
Might have a bad plug that was on a weak mag. A stronger mag can fire a bad plug easier than a weak mag.

The problem will reappear. I'm sure of it.
 
Hopefully you replaced (or reannealed) the gaskets after you took the plugs out.
 
I think every aircraft I've worked on had standard torque values for powerplant in the AMM chapter 70 and Ignitor plug R&R in AMM chapter 74. That's Gulfstream, Boeing, Douglas, Lockheed.
 
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