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?

[InitialDave]

Maybe there's some damage to the thread, might be worth getting a thread chaser/cleaner run through it?

[GreenV8S]

Normally the plug goes in until the crush washer bottoms out - since that is quite flexible you will feel the plug tighten up. If it's going solid suddenly, that can't be bottoming out on the crush washer and that suggests it must be being stopped by the thread instead. You want to fix that - the plug will be in the wrong position, maybe not sealing properly and possibly not giving the right amount of cooling, so you could damage things if you leave it like that..

[Mignon]

If you buy a long reach spark plug of the right thread or just a bolt of the right thread and grind a couple of flutes in it on the edge of a sharp bench grinder wheel you can make a serviceable thread chaser.

[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...

[InitialDave]

Couple of things you can do to minimise the risk, which have worked well for me in similar scenarios.
- sticky grease on the tap you use so any detritus sticks to it
- stuff a rag into the cylinder through the hole and spray some spray grease onto it with a stray through the plug hole, any small stuff sticks to this and you pull it out with long thin needle nose pliers (I use old artery forceps). Obviously only do this if you're sure you can get it out again!

Neither is 100% guaranteed to stop everything, but can reduce the risk of problems.

[paintman]

Wait till the other half goes out.
Find the hoover - or equivalent - and its crevice tool.
Piece of flexible plastic tube that fits down the plughole.
Tape this into the end of the crevice tool so nothing can get to the hoover other than through this tube.
Hoover out the cylinder(s)
Remove tape & tube.
Clean crevice tool & put Hoover back where your other half expects to find it.

I have a Henry for garage use!

[GreenV8S]

Mignon said:

If you buy a long reach spark plug of the right thread or just a bolt of the right thread and grind a couple of flutes in it on the edge of a sharp bench grinder wheel you can make a serviceable thread chaser.

If you bash out the core of the plug, this leaves a convenient hole for a piece of string or similar to let you retrieve whatever you shove into the bore to catch the debris from your thread chaser.