Any Spark Plug Experts Out There???

Discussion in 'Firewall Forward / Props / Fuel system' started by HomeBuilt101, Jan 27, 2020.

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  1. Jan 27, 2020 #1

    HomeBuilt101

    HomeBuilt101

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    Hi All,

    Two questions:

    -What spark plugs should I run in a TIO-540 with 7.3:1 compression pistons and a dual LSE Plasma III ignition systems.

    -How can a spark plug go bad after only 10 hours???


    I just had a NEW NGK BR9ECM spark plug go out after about TEN HOURS...

    So what can make a spark plug go bad???

    All of the spark plugs that came with the LSE kit are Denso W27EMR-C plugs and they have about 200 hours on them and they were working fine. When doing an inspection I dropped the one plug and cracked the ceramic and since the original plugs are no longer available I cross referenced to the NGK and put it in...ops check good and flew for about ten hours. Then it up and quit. To make the trouble shooting difficult I had pulled the engine out and replaced the oil pan and did some ignition wire rerouting and some other work to the airplane and then when it came time to fly the engine ran rough...lots of troubleshooting and head scratching and after the long ordeal I swapped spark plugs from #3 to #1 and the trouble followed

    As you read from my other post...the ignition system was running rough and naturally I pulled and inspected the spark plugs and there was no damage and no cracks...a bit black due to rich mixture...the idle mixture was set at sea level and I am now at 2200 MSL so I simply lean during taxi.

    SO what would cause a spark plug to go bad without any physical indication that it is bad???

    Again...the only way I found the problem was to swap the plug from #3 to #1 and the problem followed so it must be the spark plug........................

    THANKS for your help!!
     
  2. Jan 28, 2020 #2

    wsimpso1

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    Drop them and their internal resistance can go sky high by fracturing stuff inside. They can have mechanical internal connections between pieces and poor sealing, which corrodes the connections and drives internal resistance sky high. They can have defects in design and manufacture, you can get your sparkplug socket on it crooked and crack stuff... The list goes on and on.

    If you get repeated early failures with one brand and had good experience with another brand, hey change brands. My spam can uses Champions until we started getting short plug life and switched to Tempests. Saved money and back to long lived plugs. There is a big story behind it, but I believe in the old capitalist trick of voting for better products with your money. Story is that eventually Champion figured it out and fixed it, but not before they converted customers for life into somebody else's customers for life....

    Billski
     
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  3. Jan 28, 2020 #3

    Pops

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    Several years ago I owned a Cherokee for 5 years. I have had Champions plugs last one flight at the time. Must have been the same time Champion figured it out.
     
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  4. Jan 28, 2020 #4

    pictsidhe

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    I almost always use NGK. In 35 years, I have yet to have one go bad on me. I've replaced numerous dud champions, though.

    If 'Plasma' refers to an actual plasma ignition (rare), you will need special plugs. If it is a marketing word, you shouldn't.
     
  5. Jan 28, 2020 #5

    TFF

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    You have a turbocharged engine. They put lots of cylinder pressure and higher temperatures than what lots of plugs see. Auto plugs are usually 200 deg cooler running by just head contact. Turbocharged airplane engines normally have the big barrel plugs which are heavier duty than regular. Auto plugs, I would look at what the performance tuners are using. My friends RV does just fine with auto plugs, but it’s not turbo. Seen them dropped in the store, so could be just bad luck on which one they handed you too.
     
  6. Jan 28, 2020 #6

    Dan Thomas

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    I had brand-new Champs fail right out of the box. By that time I was so fed up with short plug life I just started buying Auburns for the flight school fleet. They lasted really well, and then Champion bought Auburn and shut them down. A tragedy. Auburn had the molded-in resistor that had a really low failure rate, while Champ had the carbon slug held in by a spring and screw, a lousy design that had the slug rattling around until the contact was compromised. AC came out with their Unison plug, modeled on the Auburn, and took a big chunk of the market away from Champion. Tempest bought the AC line and have grown a lot, and Champion finally had to use the Auburn technology they owned and fix their problem. They did this quietly about four or five years ago and they'll be havig fun trying to get the market back after they took so long to admit the problem.
     
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  7. Jan 28, 2020 #7

    Toobuilder

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    I have run NGK's on many airplanes over the years and have yet to find one bad. I replace them every year just because they are so cheap it's not worth my time to clean and inspect. All new ones get gapped and ohmed on install but never has one had a bad resistor. I'll bet yours was dropped in the store. Did you ohm it before install? How about at the failure?

    NGKs have one of the best QC in the industry. I'll bet yours is a significant outlier.
     
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  8. Jan 28, 2020 #8

    HomeBuilt101

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    >Did you ohm it before install? How about at the failure?

    Hmmmm...what is this Ohm testing of new spark plugs that you speak (of)???

    Wow...I never...EVER...thought of testing the resistance of brand new spark plugs but that is a great idea.

    I've only ever just checked them for damage...ran a go/no go feeler gauge through them to set the gap and a dab of antisieze (a little dab will do ya) and viola...dang this Knower OF All Knowledge That Dwelleth Behind My Computer Screen really knows his hitS!!!

    Good call I will do that hence forth...THANKS for the knowledge thus imparted!!!

    Regarding the the bad NGK spark plug...I moved it from cylinder #3 to #1 and the problem followed. I installed my spare Denso 27 in #1 and the engine ran smooth. I checked the NGK for resistance from the terminal tip to the electrode and it is Kazakly 5.00 K ohm...as advertised. So I say (now typing) "Hey WTF!!!" (Wheres The Failure)

    I do a continuity check from the threads to the ground electrode and no little beep from my multimeter...I touch the two meter probes together and I get the little beep so the meter and the beeper is working. I scratch like crazy on the threads with the probe and also scratch the bottom electrode and no beep...touch the two probes together and beep...

    So how can the ground between the threads and the electrode be bad???

    Very frustrating this thing.

    I ordered a new set of bottom spark plugs and I figure and at each annual I will do a swap of the top plugs and then bottom plugs every other year...
     
  9. Jan 29, 2020 #9

    pictsidhe

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    It's either dirty, or it has an insulation failure. Have you tried cleaning it? Wire brush is a bad idea. Bead blasting is good. To properly test it, you need a pressurised tester. Plugs are so cheap these days, the usual option is just to swap in another plug and forgetaboutit. In the very unlikely event that you fail a 2nd NGK, more investigation would be warranted.
     
  10. Jan 29, 2020 #10

    Dan Thomas

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    Watch that antiseize. It can run into the electrodes when the engine heats up and will short the plug. Got to use VERY little, and none at all on the last couple of threads.
     
  11. Jan 29, 2020 #11

    proppastie

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    unless i misunderstand are not the threads attached to the ground electrodes. ...like welded or machined from the same piece of metal?
     
  12. Jan 29, 2020 #12

    Dan Thomas

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    Yup. A beep between the electrode threads or contact button and ground electrodes would indicate a really thoroughly shorted plug. The only resistance check is between the ends of the center electrode.

    [​IMG]
    [​IMG]
     
  13. Jan 29, 2020 #13

    Toobuilder

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    4500 ohms is typical, so 5k is right in there.

    Do you have the solid tips or do they screw on? If you have the screw on types, tighten and crimp them for now, then buy solid tips from here on.
     
  14. Jan 29, 2020 #14

    akwrencher

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    This^
     
  15. Jan 29, 2020 #15

    proppastie

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    so dirty the probe would not make contact ....but that is not the point...I can not imaging checking continuity between the same piece of metal. I was thinking perhaps OP had miss-spoken. A ground could be so crusted up that it would not make contact and the spark was jumping from inside a cracked insulator to ground ( plug dropped in the store) but an almost new plug I do not think would be that crusted up. Perhaps yes though. change the plug and every thing ok so ..... problem solved.
     
    Last edited: Jan 29, 2020
  16. Jan 29, 2020 #16

    Dan Thomas

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    I wouldn't go replacing the plug if it tested at 5500. Those numbers aren't as hard as that, since that resistor is molded in there as a goop during manufacture and not-so-small variations are possible. But I have found, in Champs, mostly, resistances of 25K or 100K or 250K and sometimes infinity, far beyond any reasonable figure. Champion doubled down for awhile on their resistance failures, especially after Tempest started publishing SBs on it and giving directions on how to measure it. Champ said that as long as it sparks it's OK. But a high internal resistance encourages the spark to find other paths, especially up the (aviation) plug's lead insulator well to the steel neck. A reading of infinity implies a gap inside that is arcing internally, not a good situation at all. And a high resistance can't help but reduce both the intensity of the spark and its duration. Ohm's Law tends to be an inconvenient thing.
     
  17. Jan 29, 2020 #17

    TFF

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    High resistance is also hard on the components trying to make the energy. They are expecting the electricity to dissipate, but a backup makes more heat where not intended. Mag or electronic.
     
  18. Jan 29, 2020 #18

    HomeBuilt101

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    Thanks for the input.

    So...when I checked resistance I checked it from the tippy top of the spark plug (the terminal end identified as "A" in the attached diagram) and the little poky thing that sticks out from the center of the bottom (identified as "B") and I got kazakly 5K Ohms...perfect...

    Then I could not figure out why this spark plug would not work...the terminal end is molded on ...and not screwed on...so I cannot screw that up...

    Swapped it back and forth from cylinder #1 and #3 and the problem followed so it was not the coil/wires/cylinder pressure...

    SO...then I measured the continuity between the ground electrode (identified as "D") and the threads (identified as "C") and exclaimed "!!!WTF!!! (as indicated by"WTF" in the attached diagram).

    For some reason the electrical connection between C and D is not passing the WTF...it did work for about 10 hours and now...not so much...

    I've used a multi-meter for a bunch of years so I do know the right end of the probe and where to stick it...and I do know that where you stick your probe needs to be clean so as to make the proper connection...

    I even quadruple checked the beep...beep...beep...or was that the censoring of my actual word bombs that I dropped during this phase of the project...regardless...I can assure you that there is no beeping between C and D...

    OK...sure you say...I then stick a used (always keep a couple of old spark plugs around as a spare) in the hole and the engine runs as smooth as pudd'in...

    Go figure...noth'in a new set of Denso IK27 5312's wont fix...

    Now to figure out why my turbo is dumping out oil...AGAIN!!!
     

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  19. Jan 29, 2020 #19

    MadRocketScientist

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    That is a really random failure!

    BTW thanks for this thread everyone, I am learning a lot from it. :cool:
     
  20. Jan 30, 2020 #20

    Toobuilder

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    I have ohmed probably 100 NGK plugs and I've never seen any variation of more than 500 Ohms in that entire lot. They are TIGHT!
     

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