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Spark Plug Replacement

NC Bill

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Hi Bill,


This is a small debate and has a few different trains of thought.


The Rotax maint manual says up to 200 hrs. which to me and most in the Rotax maint educated community and the Rotax class teaching is senseless.

Rotax says to look at them, clean , re-gap and put them back in at 100 hrs. and run up to 200 hrs.

I would never go beyond 100 hours before tossing them. They cost around $2.50-$3.00 depending on where you get them. Many, like myself has been taught in a Rotax class that 75 hours is the best place. I change mine and recommend to my clients 75 hrs which came from Eric Tucker that teaches for Rotax.

The plug is the "Heart beat" of your engine and the Blood is the oil. Disease of either of these will cause down the road issues, just like smoking does to a human. It won't get you today, but just wait.


So to answer your question, you need to make that choice. 100hrs. is not a big issue and it wouldn't bother me personally, anything longer, well? I just checked a set of plugs that had 140 hrs on them and the gap was .035. Too wide.

While you are deciding now throw in 100LL verses 91 unleaded. Just love that lead.dry.gif



Do you want to be on top of the maint. curve or on the bottom?




Don't let any mechanic put anti seize on your plug threads.

(The gap is .023 - .027) (.027 for warm weather)

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As an engineer, my two cents would be "never reuse a crush gasket". If you pull the plugs to inspect them, put in new ones. The plugs don't cost $25 each and keeping a couple of boxes of them at the hanger is no big deal.

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Agreed, the plugs are out at every 100 hr insp. $25.00 is really good piece of mind, especially if you are running AVGAS.


In addition, if anti-sieze is used it will pull the threads out of the head. I had this happen when a customer brought in his CT that had been maintained by an "old school" A&P. I was able to chase the threads on 7 out of 8 spark plug holes. Guess what he had to replace????

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