Burnt spot on side of #8 Plug, single cylinder, new crate engine.

Hello all,

I'm trying to figure out whats going on with this plug. This is #8 cylinder. I recently installed a new crate engine in my suburban which has the edelbrock 3502 MPFI conversion. New GM crate engine has about 4500 miles on it. The image below is a new plug with about 2 hours of run time on it. The last new plug removed looked exactly the same. The burnt spot on the insulator is only on one side of the plug, the rest of the plug looks clean. Spark plug gap is to spec.

https://s18.postimg.org/91xeyhr9l/Splug.jpg

Attachment 12603

Any thoughts on what is causing this? My mileage on the truck is down a few MPG and I'm sure this cylinder is the cause. I'm not sure if that burnt spot is facing a valve or something else. I did a quick look with a borescope in the cylinder and didn't see anything horrifying but there was some carbon on the piston face which seemed strange for an engine with low mileage.

Any thoughts would be appreciated.

Thanks
Eric

I have seen that oil pattern with a leaky intake valve stem seal. May put an air adapter on that cylinder and remove the valve spring to inspect the seal.
HTH
Brian

if the other plugs look normal, something is surely broken..

it's a pretty bad picture but why is that ground strap so shiny? is it kind of rough like it has tiny dents?

also could be the picture but is that a chip out of the insulator?

i'd agree that an oil leak from a stem seal or guide would probably look like that, but it's hard to know for sure, the flow of gasses and particulate in combustion chambers can defy expectations.

Quote:

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I did a quick look with a borescope in the cylinder and didn't see anything horrifying but there was some carbon on the piston face which seemed strange for an engine with low mileage.

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and how did another cylinder look as far as carbon buildup goes?.. that comparison could be valuable.

The plug isn't that shiny in real life, it was the crappy little USB microscope camera that made it look that way. The truck isn't burning any oil that I can tell right now. Engine break in went well without any issues. That burned spot on the insulator shows up after just an hour or so of running with new plugs installed.

I'll do compression test all around. I re-used my old plug wires when I put in the new engine.. I have a new set coming in case this is some spark issue.

I did notice that the insulator down just a bit from the burned spot almost looks "washed" there is a second line on the insulator about 1/8th inch deeper in. Not sure why that is.

Thanks again for the suggestions, I really hope I dont need to tear apart my new engine.

-Eric

All the multipoint sequential injected v6s I maintain and tune look like this on every cylinder but in different areas around the plug depending on indexing to the intake valve always thought it was oil from stem seals or just fuel flashing on the porcelain when it's injected in and biases to one side of the valve