Spark plug threads damaged?

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TexEx

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Recently changed the cop & spark plug on the #8 because the coil was reading as bad, so I always make an effort to go ahead & change out plug since I'm there(high mileage)..as I was backing out the plug it was screaching & difficult to get out at first but eventually came out. I NOTICED a bit of slight damage to the old plug's threads but put new one in & immediately thought it wasn't seated all the way in. I torqued it to specs (25-30lbs) & put it back together. Sounded great in idle but with foot on brake & in drive noticed a rough, jumping action & also drives rough around 1800rpms. Could this mean the plug is not down completely? Btw the engine light went off after a few miles of driving as well. Ive heard of cleaning or reshaping threads with 14mm thread chaser tool will fix?? Anyone ever deal with this?
 

John Stephan

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The two rear cylinders have a tendency to collect grit into the plug wells. Did you blow the dirt out before pulling the original plug?

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TexEx

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Sure did, cranked up the compressor & used a blow stem extension, does it sound like maybe some debris may have got down in the cylinder? There was quite a bit of grime on the old plug, sure hope not..
Thx
 

John Stephan

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It's possible you pushed some in or it fell in. I'd suggest pulling the plug again, though #4 is a pain. Get a brass brush, I bought a cheap set at Harbor Freight. If you're worried about dropping the brush, turn the engine over so the cylinder is at TDC. Use a drill and some brake clean and clean the threads. 5595bc90e4bc2258aa2793db8bf50253.jpg

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TexEx

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I actually have some of those brushes, that's a great idea, certainly won't hurt, dead center tip you mentioned is important as well..thx for your feedback & time..
 
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