I am in the midst of my first annual Condition Inspection on my RV-12 ELSA (120 hours TTSN). All eight of the original spark plugs were a consistent satin tan color - amazing engine performance! I ran the engine at @ 4,000 rpm just before shutdown per ROTAX-OWNER's recommendation - maybe that helped give me the nice clean plugs? :)

While reinstalling the spark plugs, I wondered if there was any benefit in reinstalling the plugs in different cylinders to account for magneto polarity. On Lycs/Conts, I usually swapped the plug locations in a systematic manner to even out polarity wear at the electrodes. Is this procedure applicable to the ROTAX 912ULS?

Is there any advantage to at least swapping plugs "top-to-bottom-to-top" etc to account for potential lower plug fouling? Since my plugs are so clean, even that doesn't seem necessary.
  • Re: Spark Plug Polarity?

    by » 9 years ago

    Hi Dave,

    If you have the original plugs with 120 hrs. on them, toss them and put new in. I wouldn't go past 100 hrs. and many of us use 75 hrs as a bench mark. That choice is up to you.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

  • Re: Spark Plug Polarity?

    by » 9 years ago

    Its not a big deal but you should not swap positions (top to bottom, bottom to top)
    The ignition system has no distributor so a wasted spark system is used. Each secondary coil fires two spark plugs, one fires from tip to electrode and the other fires inversely from electrode to tip. If you reverse the plug it will now fire in the opposite polarity and it may damage the plug by carrying extra material from the electrode or tip. Over a few hundred hours this could cause excessive wear.

    Like Roger says,just toss them out and put new ones in.

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