Scorch marks on LSE plugs

After taking my RV-7 on an extended vacation - flying 42 hours in the past three weeks - I had a punch list of items to check upon return to my own hangar and tools. First item of business after pulling the cowl was to do a complete wipe-down of the engine and look for any obvious issues.

I found the #2 and #3 top plugs (Light Speed Engineering Electronic Ignition) had scorch marks on them. The picture above shows a comparison of #2 to #4 plug. The #4 plug is clean, the #2 plug has a brown tint on the porcelin outer case.

I will be replacing all four plugs, but I'm concerned about this and would like to prevent it from happening again.

edit: I verified torque on all plugs - they were properly torqued according to LSE specs.

It would be interesting to know how many total hours are on the plugs, how you were running your engine (CHT's), TT on engine, plug type, etc. They look quite a bit more oily than mine do, but that could just be the way the photo was taken.
I run about 60 LOP and my plugs look dry and "earthy" color, not black. I have had "bad" auto plugs before, I had a few of them when I ran Autolite 386's. Since I switched back to NGK BR9ES, I haven't had any.

Similar look with my dual PMags

FWIW, I have some of my plugs look that way also. I have dual PMags, but they don't all look that way. I haven't tracked which ones are like that or not, but it's not all the top or all the bottom. I haven't had any spark plug problems in terms of operation in 400 hours, with some over 100 hours on the plugs.
I'll be interested if anyone has knowledge of what caused this.
I run LOP unless I'm flying formation.

Seb Trost
RV-7A w/IO-360
Boulder City, NV

Specs

I run about 50* LOP at least 95% of the time. 2400 RPM, about 380* CHT, and 140 hours on the plugs. The plugs are NGK BR9ES that came with the LSE from Klaus. The engine / plane both have 140 hours on them. I ran the engine 100* ROP for the first 25 hours.

Regarding the oily appearance, the plugs are definitely black, not "earthy" brown.

Mag checks are done at every run-up at 1800 rpm. I get about 20 RPM drop when I cut out the mag, and about 100 rpm drop when I cut out the LSE.

I usually cruise at 8,500 to 12,500' but this week I spent about 1/2 hour at 15,000 feet. Don't know if that makes a difference.

I have similar scorching

I have one LSE and one mag.
at 75 hrs, I was getting a light miss from lead fouling on the bottom plugs (a/c plugs on the mag). So just to be sure, I changed all the plugs and found the same brown scorching that you show, maybe not quite as dark.
My plugs are from LSE, but they are Denso W24 EMR-C.

Just like Bob Brown said above, however, your plugs look very wet. Mine are milkshake tan and bone dry.
I run 2400/24" with 50 LOP. I get ZERO mag drop with the mag off on the LSE, and 40 rpm drop on the mag with the LSE off.
My CHT's are 320-330F in an angle-valve IO-360.

I lean very aggressively on the ground.

common question....

As most auto mechanics will tell you, there is no cause for alarm when you see the brown deposits on the plug porcelain just above the hex on auto plugs. Questioning an AC Delco engineer about the issue several years ago, I was told it is a discoloration caused by the compound used during the assembly of the plug. The application of the compound is somewhat irregular during the manufacturing process, and some may linger in the swage at the top of the hex.
This will turn brown as it gases out. Long regular vertical streaks, emanating from the hex to the boot line, however, can indicate a cracked and leaking insulator.

Regards,
Chris

Looks like Chris has the answer. I'd still say that if all your plugs are that wet, you might have something else going on. I'm no engine guru, but I'd say if your plugs look like that, your rings might not have set correctly. Thats just a WAG on my part, you might have an engine guy look at your plugs the next time you change them.

Just as a general long term engine monitoring plan, I change out my NGK BR9ES's every 50 hrs (costs 16 bucks). When they come out, I label which hole they came out of (1T, 2B, etc) and put 'em in a baggy with engine time info for future reference. I figure if a trend develops in one cylinder, I'll have that history to go back on.

Thanks for the great tip

Thanks Chris,

This is really good to know. I wasn't too worried about it, but it will be completely off the radar now. Amazing the range of knowledge that shows up on the forum....great tidbit,
thanks again.

carguy614 said:

As most auto mechanics will tell you, there is no cause for alarm when you see the brown deposits on the plug porcelain just above the hex on auto plugs. Questioning an AC Delco engineer about the issue several years ago, I was told it is a discoloration caused by the compound used during the assembly of the plug. The application of the compound is somewhat irregular during the manufacturing process, and some may linger in the swage at the top of the hex.
This will turn brown as it gases out. Long regular vertical streaks, emanating from the hex to the boot line, however, can indicate a cracked and leaking insulator.

Regards,
Chris

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