Ever have to replace a spark plug away from home?

Ever had a spark plug “fail” away from home? If so how many hours have you flown per failed plug?

  • No

    Votes: 28 82.4%

  • Yes < 500

    Votes: 1 2.9%

  • Yes 500 - 999

    Votes: 2 5.9%

  • Yes 1000 - 2000

    Votes: 1 2.9%

  • Yes > 2000

    Votes: 2 5.9%
  • Total voters
    34
  • Poll closed .
Salty

Salty

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Salty
Seems like carrying spare plugs is pretty common. I don’t really get it. A plug isn’t going to fail that often and it’s pretty easy to get a replacement.
 
1100 hrs and no sparkplug failure. I do carry a spare, an older still serviceable plug. I also carry an assortment of tools, about 10 lbs. Including spare screws, lock wire / pliers, etc.

I have had an alternator bearing and brush failure around 400 hours and diverted to Sedona. Had a replacement Fedexed but still took a couple of days. Had all the tools for working on it except for a voltmeter (needed for trouble shooting). Local Walmart came in handy for that.
 
No. Not in the last 35 years of flying anyway!
 
IN 8000 hours/70 years no plug failure in my airplanes but I have had in my 66 Mustang. Since I only believe in fine wire plugs it could be expensive to carry a spare.
 
Yes, latent ceramic crack. Two spares carried from then on. Never needed subsequently > 10 years.
 
One can carry spare stuff and never use it. Murphy makes sure of that. It will be something you don't have that fails and grounds the airplane.

If you're going to carry spares, carry the stuff that never gets the periodic inspections it should. Magnetos, vacuum pumps and alternators are all being run to failure, based on the stories we regularly read here.

Much wiser than a baggage compartment full of spares would be to do the recommended inspections and save yourself the risks and inconvenience of that stuff packing up.
 
MooneyDriver78 said:
I would carry 2, engine monitor will tell you which cylinder, but not which plug.
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It will tell you which plug... do an in flight mag check!

the standard Lycoming arrangement is below. Verify during oil change how your engine is wired.

1. 2. 3. 4.
Top L. R. L. R.
Btm R. L. R. L.

Paul
 
Salty said:
Seems like carrying spare plugs is pretty common. I don’t really get it. A plug isn’t going to fail that often and it’s pretty easy to get a replacement.
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Not always easy... most recently, we flew to Sunday lunch. Bad plug on runup, for the return. No shop on the field. Suppose you could take off with a known deficiency, but our pilot passenger was uncomfortable with that. So we identified and changed that plug.

Paul
 
Anything can break. Can't carry spare everything. Heck, I bet not many of us carry even a decent set of tools.
 
I don't have an engine monitor but it's easy to tell which plug is bad. Run the engine on the rough mag and feel for the cool cylinder with your hand.
 
I carry one in my on-board tool kit. Only time I thought I would have to replace one was a bad mag check that wouldn't clear by leaning during run-up. Pulled the plug and it turned out to be a big carbon flake between the (massive) electrodes. Just cleaned it out, and was good to go with the old plug.
 
Never had to change a plug in my plane, but I DID help another pilot trouble shoot a fouled plug in his plane at a flyin once. I had the wrenches and a good used plug in my baggage compartment that we installed. Yes..I am an A&P...
 
Snowmass said:
I don't have an engine monitor but it's easy to tell which plug is bad. Run the engine on the rough mag and feel for the cool cylinder with your hand.
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That works. Even safer is a cheap infrared laser thermometer. Just aim it at the exhaust risers, which get cool real fast on a dead cylinder.

upload_2022-6-15_10-59-42.png
 
I use that same gun. Also keep a grease pencil in my bag to put marks on the risers. Fire it up for a few seconds and check to see which one burns off the marks. Works well when I’m a pinch remotely anyway.

The reason I came back to this thread is because it finally happened. Had a totally dead plug. Verified, installed new plug, problem solved.
The strange thing is the way we discovered the problem. Student was doing the mag check, which looked good at first. I asked him to do the check again I felt a bit of vibration. He did a quick check and it was good again. I had him leave it on each mag for a longer time, and sure enough the engine began sputtering, followed by a huge decrease in RPM.
It would have been easy to have missed this problem in the run up pad. I’m thinking about changing the way I check mags now because of this. Rather than the normal quick check, I’m going to leave it in each position longer. Maybe 10 sec.
 
After landing I like to cycle the ignitions before shutting the plane down. Wonder if others do this?
 
Daleandee said:
After landing I like to cycle the ignitions before shutting the plane down. Wonder if others do this?
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I’ve never seen anyone do this, but not a bad idea. Better to find a problem after a flight than before!
 
Jdm said:
I asked him to do the check again I felt a bit of vibration. He did a quick check and it was good again. I had him leave it on each mag for a longer time, and sure enough the engine began sputtering, followed by a huge decrease in RPM.
It would have been easy to have missed this problem in the run up pad. I’m thinking about changing the way I check mags now because of this. Rather than the normal quick check, I’m going to leave it in each position longer. Maybe 10 sec.
Click to expand...
This is caused by a weak spark, not an absent spark. The cylinder doesn't get lit off properly, or on every firing, and unburned fuel accumulates on the cylinder walls and the mix then gets too rich to fire and it starts to stumble like that. Bad plug, in your case.

Some engine installations are bad for this. The R182 has the HA-6 carb, and Lycoming specified particular settings for that carb on the O-540-J3C5D. It runs rich in full-rich. Ridiculously rich, maybe for better cooling? Anyway, I complained to the Precision Airmotive people (who made that carb at the time) and they told me that Lyc wanted it that way. I told them that pulling the carb heat on downwind made the engine barf and hiccup something awful, so I had to tell the instructors to lean it to keep it smooth and safe. It could conceivably load up enough to just quit in an overshoot. Doing the runup on that engine would produce some scary mag drops, with RPM constantly decreasing if you waited, so to get RPM drops within limits it had to be leaned some. We replaced the engine at TBO with a Lyc factory reman, new carb and all, and it did the same thing, so it wasn't just a bad carb.

Problems with that arise when pilots trained on airplanes that are happy at full rich start flying airplanes that demand more careful and intelligent handling. Those pilots have been spoiled by other, more idiot-proof setups.
 
Daleandee said:
After landing I like to cycle the ignitions before shutting the plane down. Wonder if others do this?
Click to expand...

I do ignition checks sometimes after a long taxi back to my hangar...does not hurt to check, since I have to scavenge oil back into the tank before shutting down anyway.
 
Almost had to change one, but ultimately cleared up on very aggressive engine run up with an A&P after several unsuccessful tries on my own. I knew which cylinder was the problem because of an isolated miss on a reduced power instrument procedure during landing and susequent increased EGT on that cylinder. The ground run up the next AM also showed the high EGT cylinder. After getting rid of the Champions for Tempest, when back home, no more issues.
 
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