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Spark Plug Mania


Bolter

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I failed my mag check, and based on my engine monitor, I knew it was one of the plugs on the #2 cylinder.  I was not surprised, I noticed that #2 cylinder was running high EGT, visible even when taxiing.  FWIW, I had not noted cylinder #2 running abnormally on my last flight, so this happened during landing or while taxiing when I would not be watching the monitor as closely.  

Easy enough.   I was not sure which plug was on which mag, so I started with the top plug because I am lazy, and this only required the top cowling to be removed.

I found the plug with the cracked insulator (picture) and some fouling.  Eureka!  Sub my convenient spare plug in and I should be fine.

Not so fast...

Went to run up, failed again, the exact same way.  #2 cylinder when running left mags. 

Hmmm.

I went and bought a new plug, and decided to get all 8 while I was at it.  This is the second time I found a cracked champion with less than 300 hours, from the same batch.  None were dropped.  Scrap them all, and switch to Tempest, is my proactive thought, now.  From what I read here on MS, others have had problems with Champions in the recent years.  

I got back to the plane today, and removed the #2 lower plug, and found this ghastly mess (picture).  Needless to say, two new plugs installed and it runs fine.  (will do the other 6 later)

First, how many of you would have stopped at the cracked plug and thought you must have found the root cause?  

Second, am I right in thinking that since I replaced the cracked plug and had no change in mag check, it means that when mag check failed the first time, I was running on the cracked plug and for some reason, the lower plug got super-fouled for the first time ever.  I do not normally foul plugs.  What can cause this sudden change in behavior?  Is there an important underlying cause I should watch for?

I am a huge fan of the engine monitor, and I use it.  I have not seen any changes in behavior of any cylinder, and in the test flight today, everything was back to normal.  If it was a clogged injector or vacuum leak, I should see that now.

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The plugs show almost no wear. The electrodes look brand new. The cracked insulator is usually caused by some severe trauma like overtemp or detonation. The severely fouled plug can only be caused my a very bad cylinder. It is not a plug problem, your engine is crying for help.

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IIRC, in the IO-360, the left mag runs the lower plugs on the left side, e.g. #2 and #4.  So if the left mag failed on the runup on #2, it was the #2 lower spark plug that was not igniting.  The cracked insulator on the #2 top plug was a red herring (although worth replacing).

So the question becomes why your #2 lower plug is so fouled. 

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1 hour ago, N201MKTurbo said:

The plugs show almost no wear. The electrodes look brand new. The cracked insulator is usually caused by some severe trauma like overtemp or detonation. The severely fouled plug can only be caused my a very bad cylinder. It is not a plug problem, your engine is crying for help.

Bad cylinder in which way?  What symptoms would I see?  High CHT and low EGT on the #2?  High vibration?

1 hour ago, jaylw314 said:

IIRC, in the IO-360, the left mag runs the lower plugs on the left side, e.g. #2 and #4.  So if the left mag failed on the runup on #2, it was the #2 lower spark plug that was not igniting.  The cracked insulator on the #2 top plug was a red herring (although worth replacing).

So the question becomes why your #2 lower plug is so fouled. 

Agreed.  That matches my observations and thoughts. 

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Not sure exactly what could cause the broken plug. It looks like it got real hot. Was there anything unusual going on with the EGTs and CHTs ? Have you checked your GAMI spread to see if you have any rich or lean cylinders? 

As far as the severely fouled plug is concerned, those deposits came from somewhere. And that plug looks like it was running cold. Both of 6hose things could indicate a very rich mixture in that cylinder.

How long had it been sense those plugs were cleaned?

have you checked your timing?

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Not sure exactly what could cause the broken plug. It looks like it got real hot. Was there anything unusual going on with the EGTs and CHTs ? Have you checked your GAMI spread to see if you have any rich or lean cylinders? 

As far as the severely fouled plug is concerned, those deposits came from somewhere. And that plug looks like it was running cold. Both of 6hose things could indicate a very rich mixture in that cylinder.

How long had it been sense those plugs were cleaned?

have you checked your timing?

Read this:

https://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf

 

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Thanks for the feedback, @N201MKTurbo  As there is no history of fouling plugs, maybe the cracked plug made the cylinder run cold?  That prompted that other plug to foul?  I immediately noted that the #2 EGT was atypically higher than the rest when I was idling around and doing runup, when the problem existed.  CHT's are all relatively low at that point, so I cannot draw a conclusion there.  This was distinctive and obvious to me, so I am inclined to think that the plugs were both firing during my last flight, which was only 20 minutes long at 3500' from a nearby airport (KWHP), or I would have noticed.

More background: My IO-360 runs well, historically.  The last cylinder to peak is #4 and the GAMI spread is less than 0.5.  I did not repeat the test with the plugs installed this week, but saw that the cylinders were also nice and even as usual, when ROP, flying the pattern.  I do random mag checks LOP at altitude, and it always checks out.  Mags (twin pack) rebuilt last annual (November) so are about 100 hours since overhaul.  Spark plugs are 300 hours from new and I inspected them last annual.  Gave a token cleaning because they all looked good, clean, gapped and balanced to each other.  Engine is around 1100 hours SMOH, 700 hours of which are mine.  

I watch the engine monitor closely, and have never overheated the cylinders.  I keep below 380°F always, most of the time 360°F.  From takeoff to climb to cruise.  So I have good baffles and well adjusted cowl flaps.  When LOP, my fuel flows are less than 9 GPH, so I am 65% power or less.

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Well it is possible that the plug broke from an internal flaw and nothing you did. When one plug stops firing the EGT will go up significantly. This may have caused the lead fouling. I would replace the broken one and clean the fouled one and fly it for a few hours and reinspect the plugs.

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42 minutes ago, Yetti said:

There looks like some material on the lower plug.   Have you melted a piston or something? Borescope is your friend.

I agree it looks that way, but in-person, with my loupe, it did not look like metal.

That said, I am planning to borescope (Amazon USB cam style) before next test flight.

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It appears something is unusual with the cylinder, or fuel, or oil, getting to the cylinder...

1) You can post some engine monitor graphs to see what other people can see.

2) We also have a direct line to Savvy.... for an experienced set of eyes for your graphs.  Seeing if Paul is around today...  @kortopates

 

If I read this correctly you have had two damaged plugs in the same cylinder... not at the same time?

 

One of the causes for damaged plugs could be engine timing and pre-ignition...

Something to keep in mind.

 

You might be able to visit the spark plug manufacturer’s website for pics and causes of typical plug failures... (Rich did this already for us) thanks Rich! :)

Taking into account what the esteemed @Yetti is saying... get a really good look at what is on that spark plug... post a few pics...

is that aluminum on the build up? if the timing has advanced and pre-ignition is going on, a piston may be going away... quickly.  A hole in the piston can occur under these conditions during a short climb...

Do you have a local mechanic with a dental camera and ignition timing equipment? 

Aluminum melts at 1,221°F for reference.  It is the boundary layer conditions of the fuel air mixture that keep the pistons from melting. Ignition timing and Engine knock has the ability to break up the needed boundary layers...

This can occur with out any feeling of vibration out of the ordinary...

CHTs typically get extra hot when ignition timing has been adjusted too far BTDC...  seeing any hot CHTs? Or any unusual EGT to cause a single hot CHT?

PP thoughts only, not a mechanic... not trying to induce any un-needed fear...

It would be great if you can post the graphs of EGT and CHT from the engine monitor...

Best regards,

-a-

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Boy Dan, that a pair of the worst spark plugs I have seen in some time!! Holy cow!

Indeed like Rich pointed out above, I'd want to take a closer look at that #2 cylinder - both a warm compression test and borescope. These days a very good articulating borescopes are very reasonable and this one for $200 is awesome https://www.amazon.com/Vividia-Ablescope-VA-400-Borescope-Articulating/dp/B00GY7C9ZW/ref=sr_1_21?s=industrial&ie=UTF8&qid=1537651824&sr=1-21&keywords=borescope 

But the preponderance of oil at the bottom could be due to leaky rings or valve guides. The compression test could be a good first clue to leakage past the rings as you listen to where the air goes.

But the bigger concern is that the bottom plug looks so bad that it must have been offline for some time meaning perhaps several takeoffs where done without it? But maybe that was just one long flight that fouled that bottom plug so badly.

 I am pretty sure Dan is already familiar with this but I'd thought I include a brief description of how to do a run-up with your engine analyzer for other pilots that may not be aware to avoid ever taking off with this condition. During the normal run up, after temps stabilize at your run up rpm, put the engine analyzer into Normalize mode so that all EGTs are in the middle of their respective bars. Then switch to one mag. You should see every plug rise in EGT without exception. Without a rise that cylinder is probably already running on one plug. (If so, see what happens next on the other mag). Then go back to both and watch the EGT temps come back down to the middle of the bar. Then switch to the other Mag. Once again they should all rise without exception. But if you has one that didn't rise at all on the other mag, now you'll likely see that cyl EGT drop off the bar - it just went cold because the only plug that was firing just got turned off. Every run up should be pay attention to these details and give each isolated mag a few seconds to observe the rise - they are far more important than monitoring the RPM drop - which I would ignore and instead watch for the EGTs to rise. 

For the more advanced, the full rich mag test is not as revealing as doing a lean one, preferably in flight. You might be more likely to discover a weak plug with a lean mixture. When doing so you really do need to ignore the RPM drop limits, if doing this on the ground since a lean mixture can result in easily exceeding them, but instead continue to look for the all important rise in each plug on a single mag. The details are much more readable in the downloaded data with a sampling rate of every 1-2 sec. Set up a free account on Savvy to monitor the data, our free web tools make this pretty straight forward.

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53 minutes ago, kortopates said:

I am pretty sure Dan is already familiar with this but I'd thought I include a brief description of how to do a run-up with your engine analyzer for other pilots that may not be aware to avoid ever taking off with this condition. During the normal run up, after temps stabilize at your run up rpm, put the engine analyzer into Normalize mode so that all EGTs are in the middle of their respective bars. Then switch to one mag. You should see every plug rise in EGT without exception. Without a rise that cylinder is probably already running on one plug. (If so, see what happens next on the other mag). Then go back to both and watch the EGT temps come back down to the middle of the bar. Then switch to the other Mag. Once again they should all rise without exception. But if you has one that didn't rise at all on the other mag, now you'll likely see that cyl EGT drop off the bar - it just went cold because the only plug that was firing just got turned off. Every run up should be pay attention to these details and give each isolated mag a few seconds to observe the rise - they are far more important than monitoring the RPM drop - which I would ignore and instead watch for the EGTs to rise. 

For the more advanced, the full rich mag test is not as revealing as doing a lean one, preferably in flight. You might be more likely to discover a weak plug with a lean mixture. When doing so you really do need to ignore the RPM drop limits, if doing this on the ground since a lean mixture can result in easily exceeding them, but instead continue to look for the all important rise in each plug on a single mag. The details are much more readable in the downloaded data with a sampling rate of every 1-2 sec. Set up a free account on Savvy to monitor the data, our free web tools make this pretty straight forward.

Yep, this! 

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1 hour ago, carusoam said:

1) You can post some engine monitor graphs to see what other people can see.

If I read this correctly you have had two damaged plugs in the same cylinder... not at the same time?

CHTs typically get extra hot when ignition timing has been adjusted too far BTDC...  seeing any hot CHTs? Or any unusual EGT to cause a single hot CHT?

PP thoughts only, not a mechanic... not trying to induce any un-needed fear...

Thanks for summary. To your questions:

1) my JPI's recording feature is broken.  I have not gotten it fixed.  I do watch it like a hawk, and anything that is a trend would be noted. Just as I noted immediately on start the #2 was high EGT, so the failed mag check was not a surprise at that point.  Similarly, I had never seen a high #2 EGT before that time.

2) timing *was* right, but if it slipped, that would be a problem.  However, I should see an atypical airspeed-power-fuel flow combination in cruise.

Small correction: The two damaged plugs were at the SAME time.  Not two separate failures.  They were found in two steps.  The engine was running on the cracked plug, and the fouled plug was dead (per the engine monitor).

Very concerned PP thoughts...

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9 hours ago, N201MKTurbo said:

Not sure exactly what could cause the broken plug. It looks like it got real hot. Was there anything unusual going on with the EGTs and CHTs ? Have you checked your GAMI spread to see if you have any rich or lean cylinders? 

@Dan at FUL, is there any possibility that you have the wrong spark plugs for your application?  For example, if the spark plug had the wrong heat rating?  @kortopates, could that account for the cracked or fouled plugs?

 

 

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1 hour ago, kortopates said:

Boy Dan, that a pair of the worst spark plugs I have seen in some time!! Holy cow!

Indeed like Rich pointed out above, I'd want to take a closer look at that #2 cylinder - both a warm compression test and borescope. These days a very good articulating borescopes are very reasonable and this one for $200 is awesome https://www.amazon.com/Vividia-Ablescope-VA-400-Borescope-Articulating/dp/B00GY7C9ZW/ref=sr_1_21?s=industrial&ie=UTF8&qid=1537651824&sr=1-21&keywords=borescope 

But the preponderance of oil at the bottom could be due to leaky rings or valve guides. The compression test could be a good first clue to leakage past the rings as you listen to where the air goes.

But the bigger concern is that the bottom plug looks so bad that it must have been offline for some time meaning perhaps several takeoffs where done without it? But maybe that was just one long flight that fouled that bottom plug so badly.

 I am pretty sure Dan is already familiar with this but I'd thought I include a brief description of how to do a run-up with your engine analyzer for other pilots that may not be aware to avoid ever taking off with this condition. During the normal run up, after temps stabilize at your run up rpm, put the engine analyzer into Normalize mode so that all EGTs are in the middle of their respective bars. Then switch to one mag. You should see every plug rise in EGT without exception. Without a rise that cylinder is probably already running on one plug. (If so, see what happens next on the other mag). Then go back to both and watch the EGT temps come back down to the middle of the bar. Then switch to the other Mag. Once again they should all rise without exception. But if you has one that didn't rise at all on the other mag, now you'll likely see that cyl EGT drop off the bar - it just went cold because the only plug that was firing just got turned off. Every run up should be pay attention to these details and give each isolated mag a few seconds to observe the rise - they are far more important than monitoring the RPM drop - which I would ignore and instead watch for the EGTs to rise. 

For the more advanced, the full rich mag test is not as revealing as doing a lean one, preferably in flight. You might be more likely to discover a weak plug with a lean mixture. When doing so you really do need to ignore the RPM drop limits, if doing this on the ground since a lean mixture can result in easily exceeding them, but instead continue to look for the all important rise in each plug on a single mag. The details are much more readable in the downloaded data with a sampling rate of every 1-2 sec. Set up a free account on Savvy to monitor the data, our free web tools make this pretty straight forward.

It is quite something to impress you @kortopates.  Maybe you want to pop over to FUL and see them in person :-)

I feel quite confident the fouled plug was only recently failed.  #2 EGT was not atypical until this start-up and overall performance was standard for the conditions on the last day of successful flying.  If it was slowly building up junk, I would not be able to tell, but I think it must have been sparking.  

I always watch EGT when doing mag check.  The last flight before failure showed all cylinders firing consistently on each mag...or I would not have taken off.  

My last LOP mag check at altitude was good, and one trip before this event (about 4 hours of flight time).  This is based on vibration and watching EGT's in real time.  Not downloaded.

If it is rings, shouldn't both plugs be fouled equally?  Light seepage gets the lower plug, but heavy blowby should get both equally?

Edited by Dan at FUL
added questions on ring leakage
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3 minutes ago, jaylw314 said:

@Dan at FUL, is there any possibility that you have the wrong spark plugs for your application?  For example, if the spark plug had the wrong heat rating?  @kortopates, could that account for the cracked or fouled plugs?

 

 

Always possible.  I bought what was in the book, and they visually matched what I replaced.  That said, if the previous owner had the wrong ones installed, I would have just been carrying over the error. 

Champion RHM38E, for the record.  

Though it is interesting that the cracked plug is used to say the cylinder is too hot, and the fouled plug is used to say the cylinder is too cold.  

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17 minutes ago, Dan at FUL said:

If it is rings, shouldn't both plugs be fouled equally?  Light seepage gets the lower plug, but heavy blowby should get both equally?

The bottom plug is in a much harsher environment than the top and will get dirty and foul well before the top plug. Then once it goes cold, it accelerates as what must of happened with your lower plug. If you had the data, it might be possible to go back to the last flight and see the EGT2 first rise. But challenging that is that at first it could be an erratic rise which would help to mask that it has risen once it stayed high. 

I don't know what your CHTs are running at in cruise but assuming they are in the normal 300-375+F range I doubt the plug's heat range could contribute to the issue. 

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