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Spark Plug Oddity

bjdecker

Well Known Member
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For the hive-mind...

Attached pic are the Denso IK27s that I've been running in my IO-360-A1B6 with Dual Lightspeed Plasma III's for about 150 hours.

I typically operate 50 - 75F LOP, CHTs ~290 - 320F range. There has been no indication of ignition issues, no backfire, no stumbles, no runaway EGTs, no compression issues, etc. etc.

Any ideas what the source/cause of the discoloration around the bottom of the ceramic insulator might be?
 

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Are you using the normal red boots that come with Lightspeed? The darkening reminds me of the blackening that happens when you get black rubber hot. Many things that I have seen that use black rubber will darken and discolor the area around it, but I haven't seen anything so drastic with the red lightspeed caps. Perhaps you got oil on them at one point and that got cooked into the plug?

It does look unusual.
 
Looks like gas seal ring leakage. (not the base gasket)

Edit: I stand corrected, corona discharge - - the internet can make us smarter and dumber too. OK, but if all the plugs have the same boots why do only some have this discharge attraction ring? And why is it not always repeated on the same location. After thousands and thousands of VW plug replacements, the leakage was the common thought 50 yrs ago. There is a little more to this. OK - it did say main cause, not only cause.
 
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Interesting. I have a gut feeling that the leakage isn't correct. With the amount of airflow through at least the top of the cowl, I wouldn't expect the plugs to get much leakage that would even stay near the plug. In fact, I would say unless the torque was wrong or the plug insert was bad, I wouldn't expect any leakage. But the corona discharge thing makes sense. I've never had any come out quite that dark, however.

How long have those plugs been in service, BTW? I've ran the auto plugs as long as maybe 200 hours and never had them like that. If you went significantly longer, maybe...

I've been using the iridium plugs for a while, and will be switching to the TT plugs by denso on my next swap. Already have them ordered. Those should last quite a long while without changing gap.
 
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