Spark plug hole carbon buildup
 

I just got an 04 RX8 with 60k miles. While checking the spark plugs a little while ago, I noticed that the front rotor leading plug wasn't screwed in all the way, but it was tight. So I removed it and noticed that it has quite a bit of carbon buildup in it. It's the brownish sort of carbon like you would expect to see lightly coating a set of spark plugs, and it is about 2-3mm thick (imagine a pipe with the same inside diameter as the plug hole with water sitting in the bottom of it with a depth of 2-3mm, that's how the buildup is sitting).

I put some anti-seize on the plug so I could gauge how far the plug was going into the hole before contacting the carbon, and i was only able to screw it in about halfway. The crush washer has not been crushed either, so the buildup has been there since the last time the plugs were changed (no idea when that was).

My first question is, how should I go about removing this? I was thinking of trying to break it up with a screwdriver without letting it drop into the rotor housing, and then slowly turning the engine over by hand with the leading plug removed, trailing plug still in. That way, when the apex seal passes the leading plug hole it will release all of the compression into the plug hole.

My second question is, how would all of that carbon build up in there? And has anybody experienced a similar problem?

I'm very familiar with rotaries, just not very familiar with RX-8's. I have an 87 FC TII that I rebuilt and streetported myself.

Thanks.

They have sprays that will break it up.

Try brake cleaner on a rag, you have to wipe fairy soon as it evporates.

Brass brush is the best. Just brush it and your done.

The spark plug hole in the rotor housing has carbon buildup in it, it's not on the spark plug itself.

Sounds like some asshat at the dealers stripped the threads and just wound the plug in till it got tight .
Not sure how you are going to get the carbon out but when you do it may pay to run a thread chaser down it before you try another plug in there ....

You can still clean it has he mentioned! I hope they just didn't cross-thread the damn thing!
Oh course try as best you can to keep it out of the engine, but get it out of the plug hole!

I'm far from an expert but maybe try to use a shopvac or something to suck up anything you manage to break loose, or even make a small nozzle for the vac with a piece of a hose and suck it clean while you break out some of the buildup. But I dunno, just brainstorming.

a vacuum cleaner with a straw at the end?

I was able to take a tap with some grease on the end of it to break up the carbon a little bit at a time. I just went slowly and pulled the tap out of the hole often (the chunks of carbon would stick on the grease).

I'm still curious how this could have happened though. If the car would have had a bad coil at some point and had been misfiring, would the misfire have caused excess carbon buildup? Maybe the plug that would have been misfiring would have had a lot of carbon on it and a piece of carbon would have fallen off in the plug hole as it was removed, then when the new plug was put in it would have tightened up once it hit the carbon and the mechanic would have thought the plug was tight. Then, because of the plug not being in the hole all the way, more carbon would have built up or been scraped into the hole. That's the only way I see it happening.

Anyway, it's nice to be able to see into the plug hole on the RX-8 by looking through the wheel well. If this problem would have happened on my RX-7, it would have been much harder to deal with.