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Broken Spark Plug

in 912 / 914 Technical Questions 8 years ago
Hi all!

I have a 912ULS and it was time to remove the spark plugs for inspection, but on the first trial it broke inside the engine head (see attached pic)!

It probably got stuck due to lead accumulation, once I run only on avgas. I tried to warm the engine and remove it, but no success. I was thinking of taking it to a shop to remove the stuck plug but I don't like the idea of removing the cylinder head once the engine is running perfectly.

One of the solutions I thought would be to drill the rest of the stuck plug and then install a threaded insert like a Heli-Coil, but that could take metallic debris failing inside the cylinder.

Any help?!
IMG-20160409-WA0012.jpg (You do not have access to download this file.)

  • Re: Broken Spark Plug

    by » 8 years ago

    Hi Diego,

    I have never seen anything like this. The plug center porcelain can be drilled out leaving the outside of the plug intact. This would allow an easy out to be inserted and not contact the head threads. Absolutely make sure the top of the piston is at the bottom of its stroke and not TDC if you drill. It would also remove the 90 degree water tube just above it and make sure to heat that area all around the plug nice and hot to help break it free. If it is securely in place a little tapping on the plug edges with a metal rod and hammer may cause whatever has those threads locked up to break loose.

    Whatever you do, do not damage or beat on the head itself.

    This had to take some God awful force to shear a plug like this. How long were these plugs in place?
    Did you have any plug thermal paste on the threads? This would have prevented the thread seizing like this. Torquing the plugs to 177 in/lbs should not have yielded this result if the plugs were torqued correctly and with paste on the threads.
    Unless these were over torqued. left in way too long and no thermal paste applied to the threads I can't see how this happened?

    Rob,

    Do you have any words of wisdom here?

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

    Thank you said by: Diego Fonseca
      
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  • Re: Broken Spark Plug

    by » 8 years ago

    Do the job properly. Take the head off and get it on a bench.

    If you try and cut corners it will cost more money in the long run.

    If you can't do the job, get someone who can.
    Thank you said by: Diego Fonseca
      
    Report

  • Re: Broken Spark Plug

    by » 8 years ago

    As you drill away on the stuck plug use a good vacuum cleaner to keep sucking debris away.
    Thank you said by: Diego Fonseca
      
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  • Re: Broken Spark Plug

    by » 8 years ago

    I also agree with Roger Lee all the way. This stuff makes me nervous. Good luck. Let us know how you made out.
    Thank you said by: Diego Fonseca
      
    Report

  • Re: Broken Spark Plug

    by » 8 years ago

    Take the head off, once it's reinstalled the engine will run just as well as you're used to. If you screw it up you're looking at a 1500 head and you probably have the old style that is no longer available the new ones work the same but look different and if it's one with a temp sensor you'll have to re-route the wiring. I would suggest you purchase new intake manifold gaskets and pushrods tube o-rings, those items are cheap and should be replaced.

    You mentioned that you were thinking of using a hell-cool, DO NOT DO THAT. The manuals clearly state that heli-coils are not to be used for spark plug threads. The steal insert could cause a hot spot and lead to detonation issues, detonation will shit can your engine in less than a minute.

    Where are you located?
    Thank you said by: Diego Fonseca
      
    Report
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