Ive got one that wont go in far enough to crush the washer, goes in about half way dont know how the he!! this happened, thinking of using a thread chaser ?

Mercury racing aluminum heads and pucker factor is high.......

Have not had to use one, but i have my eye on it if i need to:

I'm a bit confused abt this plug pictured. Looks like half the threads were inside the combustion chamber, but I'd think the tip would be destroyed from the piston if the wrong reach??? Anyway, from the pic, it looks like a lot of debris abt half way up the threads. Try cleaning plug threads with a wire brush? If it doesn't clean-up, probably galling/metal x-fer.

I've own'ed a conventional spark-plug thread-chaser for 40+ years. Used it once on a motorcycle. I applied grease to the tap and it caught almost all the filings. Could also force exh valve open and blow compressed air thru plug hole and get any remaining filings out.

Fixed it with a thread chaser.........

F2,

So, what was the story? Tapered pitch diameter, oversized root diameter or just buggered up at "a spot"? Knowing that spark plugs are made on screw machines, at least the main body, which are consistent if nothing else, it's hard to imagine a single flyer during production. When you recut the threads, where did the chips come from specifically?

Edit.... Was the issue with the spark plug or the plug hole in the head?

Thanks. Brad.