Mag problem- Suggestions welcome

[piperboy84]

landed away tonight, Doing the mag check prior to departure and the left was coughing and spluttering and big rpm drop, switched back to both and run it up to 2200 rpm and leaned right out for about 30 seconds, still no joy, removed cowling and checked all leads for secure connection, all appeared ok.

Is there anything else before i call out the mechanic ( and ring up a bill) that i can/should do to fix the problem?

[B2N2]

Depends, not enough info.
What was the temperature? Were you taxiing with Mixture full rich or leaned?
30 seconds may not always be long enough to get rid of whatever is causing it.
Do you have a reliable EGT gauge?
**** Disclaimer, the following is based on personal experience and shared on an anonymous forum ****

I have had cases where I had to run the engine at full power with the mixture leaned to around 1500-1550 F for a long as 5 minutes till whatever was fouling the plug (usually a little lead ) was spat out the exhaust pipe.

Alternatively you may have either one of a dozen possibilities ranging from a broken lead to a disconnected ground to an internal mag failure.

[piperboy84]

more info:

The flight was from one farm to another and was for 5 minutes, mags were fine for this leg, landed, let the plane sit for 30 minutes, restarted and warmed up then had the mag problem, dont have a egt

[piperboy84]

B2nb
**** Disclaimer, the following is based on personal experience and shared on an anonymous forum ****

Understood on the disclaimer just trying to figure out if there is anything simple other than a high rpm lean out that i can do to perhaps clear it as its in a short, rough grass field and dont fancy flying it out with a bad mag, so will need to call out a mechanic from 50 miles away which will no doubt be costly,

[Maoraigh1]

Can you remove and look at the plugs? Clean any if necessary.

[stevef]

How big was the mag drop? 200rpm or so? That'll almost certainly be a fouled lower plug. Less likely but still possible is a defective plug lead.
A much bigger drop is probably a magneto fault. If there's no drop when cold but appears when the engine's warm, it'll be a condensor.
What aircraft is it?

[Dan the weegie]

It's almost certainly lead build up and you're not quite able to get the engine hot enough to move the lead.
You're perfectly entitled to take the HT leads off and remove the plugs to have a look at them. Start with the bottom ones attached to the mag that you're having a problem with :).
Just be careful when you put them back on to tighten but not overtighten them and that they are properly threaded. I asked a fellow Cub owner what torque he used and his response was "Techt".
Get a wee bit of AVGAS to clean em and a gentle wire brush and remove the lead deposits. 9 times out of 10 that's what has caused rough mags for me.
One thing you can do is get a few spare plugs from LAS Aero of the type in your engine and swap em out with badly fouled plugs.
If that doesn't clear it you may need to get help from an appropriately experienced engineer type.

[piperboy84]

What aircraft is it?

Maule MX7 180a with lycoming 0-360 with 125 hours since overhaul and complete aircraft rebuild with new mags etc, annua 4 lmonths ago.

Perhaps i did not give it enough opportunity to burn off any fouling on the plug, the CHT gauge was not too far in the green when i did the 2000rpm lean out for 30 seconds, tomorrow i will go and let it warm right up, run it for 10 15 minutes then do a high rpm lean out for 1 or 2 minutes

[Dan the weegie]

Honestly, it's better to just take the plugs out - if you know someone nearby that owns a permit aircraft, take them with you. It's not as big a deal as you might think.

[Zulu Alpha]

I'd clean and inspect the plugs. It could be a bit of lead/carbon/oil fouling one, but it could also be a duff plug.

You can try swapping the top and bottom plugs on one side.

If it changes to rough running on the other mag then it is probably one of the bottom plugs that you moved to the top.
If it is still the same mag that is giving the problem then try doing it again on the other side of the engine.
If after this it is still the same mag then it may be a mag problem.

(this is because each mag will probably run the bottom plugs on one side and the top ones on the other)

Changing a plug is probably cheaper than calling an engineer out. Most engineers would just clean and change the plugs first so you may as well do this yourself.

[Pilot DAR]

ZA is suggesting what I would be doing. Use proper tools! Removing plugs is straight forward, though using the wrong tools can cause you more difficulty. Changing plugs is probably within the privileges of the pilot/owner (it is in Canada), but satisfy yourself you do have the authority to do this work unsupervised.

Should you decide to follow ZA's advice, clean the mag lead caps at the plugs, so you can read the "T1" etc. to assure that they go back on the correct plug (lead length and position should assure this, but it's gotta be right). Hold the smaller nut on the lead (probably 7/16" wrench) while you turn the larger one (probably 3/4"). 7/8" deep socket needed for the plug. Do not drop the plug on the ground, a hard knock wrecks them. Take note of all the washers, and my be CHT lead under one plug.

Once out, and before swapping top for bottom, use a stainless steel brush (BBQ brush works) to clean the electrodes. Inspect for broken brush wires left in there before retuning the plug to the other position. Probably torque to 300 inch pounds. Really - you should use a torque wrench for that!

If you have done all of this, and a ground run satisfies you that the problem is rectified, as long as everything is done up, you're safe to fly. If that did not fix it, call your mechanic, there's nothing else you can do without direct qualified oversight.

Do not allow moisture to enter between the spark plug lead and the plug (like doing the work in the rain), you will frustrate yourself when you start the engine.

[BackPacker]

To find out what spark plug is duff, I've heard that engineers start and run the engine on the "rough" magneto for a minute or so, then shut down. The cylinder that's cold is the one with the duff spark plug (or HT lead, or whatever).

However, be advised that you are running a combustible mixture through that cylinder, but without a spark to ignite it. So the unburned mixture ends up in the exhaust and eventually in the atmosphere. You might want to make sure this doesn't do any harm, and doesn't meet another source of ignition somewhere.

[Jodel D11]

Identify the cold cylinder as described by backpacker (saves a lot of time and effort). Bring a spare plug with you if you have one, Trace the leads back from the problem cylinder to the mags, and work out which lead top or bottom goes to the rough mag.This will identify which is the duff plug.
Try cleaning the plug first. If no joy change it. if that does not work change plugs top for bottom, if it is a problem lead you will still have the rough running on the same mag, and probably need an engineer.
With an aircraft on private category changing of plugs is allowed under pilot maintenance.

[Zulu Alpha]

To find out what spark plug is duff, I've heard that engineers start and run the engine on the "rough" magneto for a minute or so, then shut down. The cylinder that's cold is the one with the duff spark plug (or HT lead, or whatever).

This is also a good idea, but use the exhaust temp rather than the cylinder.. You don't need to run the engine for more than 30 secs as the exhaust heats up quickly. you can tell by touching them which one is cold or cooler.

[A and C]

The plugs should be torqued to 30 ft/ lb and the threads should have a little graphite anti-gauling compound put on them before re- fitting.

The only thing is that I have yet to be convinced that it is a problem with the plugs, AVGAS has a compound in it to encourage the evaporation of the lead, this compound starts to work at the temperature developed at between 1600-1800 RPM. This leaves me doubting that it is lead fowling problem as it was reported the engine has been run at 2200 rpm and that would most likely have cleared the lead fowling, so may be it is oil fowling or a malfunction inside the Mag. A little more info on the scale of the mag drop would be helpful.

[DeltaV]

Not sure how you evaporate lead other than, possibly, with infeasible amounts of heat. I've seen beads of metallic lead, not lead ash, in and removed from the annulus of plugs pulled from the engine of the local flight school aircraft. For that to form conditions in the cylinder have to be 'reducing' ie. not oxidising, so maybe the engine was running overly rich.

No help with the OP's mag drop question, just commenting on A and C's lead fouling post.

[Dan the weegie]

I'm the same, all of the planes I've owned that ran on AVGAS needed plugs removing and small chunks of lead removed these were busy planes as well though, quite often you just get a little bead on the plug that shorts it. post cleaning all was well for another 30 hours or so of flying.

[Mark 1]

TCP or Decolin added to the fuel is the most effective way of reducing lead fouling in my experience. It converts the lead to a powdery salt that won't accumulate. It also has the benefit of keeping fuel valves free-turning; that may be anecdotal, but true in my experience.

REM37BY plugs and the fine wire (expensive) versions are more resistant to fouling, but not immune. You need to check which alternatives are valid for your engine.

[piperboy84]

Sorted ! Now THIS is what this forum is all about, people helping people.

Copied and pasted all the replies here into a word doc and loaded up the Landy with the laptop and the tools PilotDar listed, swung by Perth and bought a plug then drove with my dad (he’s 78) over to the pasture where the plane was. Removed the top cowling and fired it up, switched to the left mag (the rough one) and ran it for 30 seconds, jumped out and found the forward left cylinder head was cold the rest were nice and toasty. Traced the lead from the left mag and it was the bottom plug which involved removing the bottom half of the cowling. Did not want to disconnect all the air hoses so loosened it off and had the old man on all fours under the plane with the cowling resting on his back. The first problem was I did not have a plug key deep enough to remove the plug, I did have a socket that was long enough but was a few sizes too big, after sticking a bit wire and some paper in the socket and some advice from my dad along the lines of “hurry up you useless bastard” and “this is killing me being under here” I got the plug replaced all with a 30MPH wind blowing. Fired it up and all was well, waited for the wind to die down a bit and flew back to the home strip with the Maule now safely tucked away in the hangar.

Thanks to all for the advice it is greatly appreciated.

[BackPacker]

Did you take a look at the duff plug to see if it was contaminated in any way?

Furthermore, with that improvised socket it seems hardly likely that you were able to torque the plug to the proper tension. You might want to ask somebody with the proper tools and experience to double-check your work.

[Jan Olieslagers]

I do hope you found due and ample compensation for your poor old dad - MY son could not count on me for that kind of exercise, unless WELL made up for! Best might actually be to tell all and sundry that without his sound recommendations, you could never have managed.

[Dan the weegie]

30lbft torque is just a little beyond when the resistance requires effort, too tight is bad :) techt, but nae too techt :). I would definitely buy an appropriate socket and a torque wrench, this is not the last time you'll be taking a plug out.

More often than not you'll be able simply to clean the plug with avgas a wire brush and a wee bit of metal to pull the crud out. Replacing them with a new one is expensive and rarely necessary :).

[B2N2]

**** TOO LATE ****

I would be very hesitant myself to change a plug without having received instruction in doing so by a certificated mechanic.
Legal does not always mean wise, FAA-land or EASA-land.
Tinkering with the ignition on my car I dont mind, if it stalls at the end of the driveway it wouldn't kill me.
Just a future recommendation; there is a bunch of stuff you are legally allowed to do as an owner. Take this list and decide what is likely to occur to you considering the type of flying that you do, unattended farm strips.
Take some instruction from a mechanic and carry the basic tools to do:

Tire change or tire repair
Plug change or cleaning
Oil change
Basic fabric patch
Battery charging or replacement
Landing/taxi light replacement