What would cause fouling on just half of the spark plug?

[BMac Attack]

I was having issues with my newly installed “Hecho en Mexico” base GM Goodwrench engine. I’ve put about 1500 miles on the truck since the install and it was missing and running rough. I pulled the spark plugs after double checking that the timing was at 12 degrees and found that number 1 was completely oil fouled and 3 had a distinct line of demarcation where half the plug was oil fouled and the other half was clean. All the rest of the plugs looked good except for every single one of them had oil on the threads. I’m learning to wrench on my own truck and haven’t seen anything like this before. After new plugs, she was running great again. Would you say that my valve cover gaskets are leaking?
1986 K20 SM465 350 base small block, edelbrock intake and edelbrock 1406 carburetor.

 

[Radiohead]

Would you say that my valve cover gaskets are leaking?

No, but near by. I think you meant valve stem seals. I believe it is a distinct possibility. Not sure why one plug fouled on only one side, but leaning on the theory that it is another leaky stem seal at half speed of the other, worse one.

 

[BMac Attack]

Would the leaky stem seal(s) cause oil to be on all the threads of the spark plugs? Although virtually new, this engine sat for a long time. I believe it sat for about 4 years in a garage, before I got it - is that sitting around what could make the stem seals go bad?

 

[fast 99]

No, I was going to ask if the engine could be warrantied, 4 years likely not. Buy an inspection camera, look inside. Harbor freight has reasonable one. If the edges of the piston are clean it's rings, if oily all over valve seals. intake gasket, pcv system, ect. That's a lot of oil in picture 1, not good.

I have installed many GM motors they are usually decent runners but not HP monsters. Kind of surprises me you're having this issue. Makes me wonder if at some point it was overheated or abused in some way.

 

[BMac Attack]

Unfortunately, no warranty. I bought it from a private seller off the local digital marketplace. The original motor died and I was in a hurry to get it running again. That’s a great suggestion on the inspection camera. I’ll do that and post the pics.

 

[BMac Attack]

Ok, now I’m not sure what I should do. I installed all new plugs and within 100 miles it started running really rough again and consumed about a quart of oil. I ordered some valve seals thinking that was my problem and got the tools together including a homemade air chuck welded to the bottom half of one of the old spark plugs. After pulling the valve cover, everything looks pristine which is baffling. I was expecting the valve stem seal to be gone or deteriorated in some way. It looks perfect though. This time when I pulled the spark plugs, #3 was oil fouled the worst so I removed the rockers on that cylinder and hooked up my air to hold the valves up. The valve seal looks pristine to me, as I would expect a new engine to look. Truth be told, I’ve not opened up an engine so I don’t have any frame of reference of what good or bad looks like but mine seems fine. Should I still replace the valve seals? Check out the spark plugs on that bank. Everyone is different and only #7 looks normal to me. #1 was oil fouled the worst the last time I pulled them and now it has some oil AND crusty stuff on a plug that was clean when installed. #3 is oil fouled badly and #5 has red stuff on it. I’m not sure what my next move should be - any advice would be greatly appreciated.

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[fast 99]

Slipped cracked intake or gaskets can cause one or more cylinders to use oil. Engine sucks in oil from the bottom. Will need to get it back to running condition to check that.

Assume at this point the PCV system has been checked and baffle is in the valve cover.

 

[Ricko1966]

Run compression,wet and dry. Post results

 

[nvrenuf]

I saw a video once where David Freiburger (Roadkill) was talking about how a lot of popular spark plug brands have quality issues because of outsourcing, foreign manufacturing, etc. Iirc, he recommended using either NGK or Denso plugs because they seemed to have the best quality control.

That said, since it runs good now, could it simply be a case of a poor quality product with only half of the electrode firing or maybe the whole electrode firing minimally (only enough to burn off the side facing the flame front)?

 

[Ricko1966]

I'd say a weak coil or a way too rich mixture or timing way off would be more likely. The compression test wet and dry will tell a lot.

 

[scrap--metal]

intake or gaskets can cause one or more cylinders to use oil.

Intake gasket is one good culprit.

timing way off would be more likely. The compression test wet and dry will tell a lot.

OP said he verified the timing to be 12°, so that shouldn't be it. The compression test will tell if the rings are bad. I agree that this should be the next step.

If the compression test checks out, I'd be it's the intake gasket. A quart of oil in 100 miles is a lot, and assuming it's not leaking really bad, I can't imagine it using that much oil any other way.

 

[BMac Attack]

Thanks for the replies. I will read up on what a wet/dry compression is and make that happen tonight. Is it OK to do a compression test with the rocker arms, and valve cover off the #3 cylinder? Will anything fly off (like push rods) while I’m cranking? Does that valve seal in my pic look good?

 

[Ricko1966]

Tell us how you checked timing. Step by step don't read anything first just tell us what you did. Thanks

 

[WFO]

Thanks for the replies. I will read up on what a wet/dry compression is and make that happen tonight. Is it OK to do a compression test with the rocker arms, and valve cover off the #3 cylinder? Will anything fly off (like push rods) while I’m cranking? Does that valve seal in my pic look good?

Check the compression dry first. Then if a cylinder is low, squirt a little oil into that spark plug hole. If the compression comes up it's rings, if it doesn't it's valves.
That #3 wont build compression without the rocker arms on it.

 

[Ricko1966]

I'd say a weak coil or a way too rich mixture or timing way off would be more likely. The compression test wet and dry will tell a lot.

I was putting this out there in response to him thinking he got 8 plugs that only 1/2 the electrode was firing.