Spark plug depth

I may or may not have a problem . The engine I purchased from Mattituck few years back when they were in operation recently was unpickled and started for the first time. After checking into gapping the plugs I noticed something that got my attention. The spark plug electrode seems to only extend about halfway into the spark plug hole and doesn't sit flush with the bottom of the hole like I think it really should. This is a lightspeed ignition that Mattituck installed to check on the new engine and ran it with these plugs that I received . My thinking is because the depth of the 18mm spark plug hole looks like it could be 13/16, they received 13/16 length plugs but by the time the 14mm adaptor was installed with only a 1/2" helicoil, the plug only reaches halfway into plug hole. According to what I read this can be a point of carbon buildup and potential predetonation problems? See photos to clarify what I'm saying. I emailed Klaus at LSE the photos and he says I have the right plugs and adaptors. I'm not confidently sure.

Lycoming's use plugs with 1/2" reach. The plugs used by most for EI are 3/4" reach, but the bushing has a reach of 1/2" with 1/4" spacer/nut, netting an effective plug reach of 1/2" with a 3/4" reach plug.

It is not uncommon for plugs to be slightly recessed in their threads/cavity and this does not impact performance. They are not always projecting into the chamber. Each cylinder design is a bit unique.

Larry

I am wondering about that as actually the spark plug hole doesn't look like it was bored totally for a long Helicoil to go all the way down flush with the cylinder ceiling but looks like a longer helicoil could be accepted so that longer adaptors and longer plugs could be installed.
I know the engine will run and appear alright but still wondering if this could be a potential for carbon buildup/predetonation or am being overly concerned? Since as you can see from the photos the bottom of the plug is only even with the bottom of the helicoil, halfway into hole, not bottom of plug hole.

One thing that will help a little is that I don't recall that there should be a copper crush washer under the head of the bronze adapter bushing, as you have in your picture. That will give you about a 1/10 inch more depth of fit of your plugs.

That's a good point, I'm not sure if that crush washer is for that adaptor, will have to look into that.

Looks just like my Mattituck Red-Gold with LSE adaptors and Denso IK plugs. I have more than 2,800 hours on this configuration without any issues; Klaus' advice is generally spot-on.

rvdave said:

but still wondering if this could be a potential for carbon buildup/predetonation or am being overly concerned?

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You're being overly concerned. Carbon typically only builds up if you run too rich or burning a lot of oil. In that case it will cover everything.

You are correct that very small objects can becoming glowing easily and help pre-ignition. However, you need on abnormally high amount of heat to cause that condition, such as the heat generated by detonation. The small piece isn't the cause of the pre-ignition per se, it only helps it occur sooner. It's the high heat that is causing things to glow and then pre-ignite the mixture. Your spark plug's negative electrode is all that is necessary to help pre-ignition by becoming a glow plug, so to say. I don't think a carbon chunk will help it happen any sooner. Maybe a little bit.

Small chunks of carbon don't becoming glowing under normal operation. Furhter, I don't see the plug cavity as creating a small chunk. It would be evenly spread, It is the isolated 1/8" chunks that start glowing quicklyl

Larry

deek said:

Looks just like my Mattituck Red-Gold with LSE adaptors and Denso IK plugs. I have more than 2,800 hours on this configuration without any issues; Klaus' advice is generally spot-on.

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That's great to hear, thanks for posting, that sets my mind at ease knowing the exact same configuration is out there with no problems. Also confirming Klaus' understanding of the situation.

Also thanks Larry for expounding and explaining what and how things happen in a practical scenario.

Looks like I'm good to go and no worries so I'll carry on, thanks guys.