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Spark plug analysis

in 912 / 914 Technical Questions 7 years ago
Hi everyone!

I just changed my spark plugs after 200h on my Rotax 912ULS. I would like to know what you guys think of their appearance.
The plugs from cyl. #3 have a different colour than the rest, they appeared yellowish.

[url=]PICTURE[/url]

Blue skies

Denis Ranque

  • Re: Spark plug analysis

    by » 7 years ago

    In my opinion, the #3 plugs are the only ones that look to be the right color; the others are too black (sooty). Did you run the engine at about 3500-4000 rpm for a while before you shut down to remove the plugs? Otherwise idling will soot them up.
      
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  • Re: Spark plug analysis

    by » 7 years ago

    Hi Denis,

    I can tell by looking at the pictures that your gaps are too wide. They should be between .023 -.027. A nice place to be is in the middle at .025. If you live or are flying in cold country a narrower gap is better. If you start out at .027 then the gap will only get wider and work its way out of spec.
    I know the manual says up to 200 hours, but most of us use 75 hours and I personally don't know of anyone that goes past 100 hours. For a couple bucks a piece these are cheap to keep in top condition. They are the heartbeat of your engine.
    Idling will cause dry black sooty plugs at times. If you want to do a more accurate plug color check go fly and as soon as you land pull over and check the plugs or while on the ground run the engine for approximately 5 minutes at 4K rpm then back to idle with an immediate shut down with no idling.

    As far as right now just replace your plugs with a better gap and go fly. :)

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

    Thank you said by: Denis Ranque
      
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  • Re: Spark plug analysis

    by » 7 years ago

    Thanks for the information guys!!!
    I was not aware that running at idle turns the plugs sooty. Next time I will make sure to have the engine at high RPM prior checking. However, I do remember being advised against removing spark plugs from a hot engine to prevent thread fretting. I guess I will have to wait for it to cool down :)

    Blue skies

    Denis
      
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  • Re: Spark plug analysis

    by » 7 years ago

    Hi Denis,
    You can remove plugs hot or cold. They should have thermal paste on them which helps with thread lubrication.

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

      
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  • Re: Spark plug analysis

    by » 7 years ago


    I know the manual says up to 200 hours, but most of us use 75 hours and I personally don't know of anyone that goes past 100 hours.


    Is this assuming exclusive use of 100LL?

    Aviation Real Estate Specialist & iRMT

      
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