Spark plug tightening issue

[Soneji]

Hi, was changing spark plugs when one of them didn’t feel right. As usual I turn them in by hand, and then take the ratchet to crush the collar somewhere between 1/4 turn and 1/3 but one cylinder goes from loose pretty much straight to a ‘dead stop’, I.e there’s no really flex or further rotation beyond that point of nipping up by hand. Maybe a mm or so at best.

These were the original plugs by the looks of it, and I’ve tried old one back in, swapping new about etc but no difference. Car doesn’t appear to run adversely because it.

Just curious as to why one of six cylinders doesn’t feel right?

[Soneji]

Cheers, I’ll get a chase and run it through. Should I be concerned about debris? I’m almost certain these are the original plugs, so I’m the first to remove it. Was quite tough to get that one out. Is it likely to be carbon build up? Struggling to see how the bottom of the thread down at the combustion chamber end could be damaged...