Spark plug thread

[Concrete-crusher]

Hi I have one thread number 2 cyclinder thats a bit damaged 2/3rds of the way down, it holds but I'd like to clean it up. Can sombody please remind me what tap size I need just to run down the thread and clear the bur that's clogging it?

Looking at previous threads they all seem to refer to the repair kits etc. But I wanted to just try cleaning up the original thread first

Thanks Steve

[Craven]

14mm but its quite a long thread depth.
https://www.machinemart.co.uk/p/cht261- ... ead-chaser
Sorry wrong end.

[nmauduit]

my LTC spark plugs e.g. NGK BP6ES have a metric thread diam 14mm 1.25mm pitch (though I've heard people using diam 9/16" thread 1/16", I would not)

[Lyn7]

Try looking/searching for a spark plug thread chaser as apposed to a tap. It's meant just for cleaning up the thread as, apposed to cutting a new one.

[promotor]

Try looking/searching for a spark plug thread chaser as apposed to a tap. It's meant just for cleaning up the thread as, apposed to cutting a new one.

That's what I would recommend too as they tend to push the threads back into shape rather than re-cutting them completely like a thread tap does. In aluminium it's a bit more crucial to leave as much material in as possible.

[Concrete-crusher]

Thanks put a chaser on order

Steve

[2cams70]

Put plenty of grease on the chaser to minimise the chances of metal chips falling into the cylinder (the chips, or most of them hopefully, will stick to the grease). I'm surprised the thread damage is 2/3rds of the way down. Usually thread damage is more likely to be at the lead into the thread.

[Concrete-crusher]

Yes, readers might recall I rebuilt the engine a few years back, anyway when reassembling number 2 cylinder felt a little stiff screwing back in, I should have stopped but didn't, anyway when I next took the plugs out I noticed the damage. I assume maybe a contaminate got onto the thread. Engine runs really well but I know I need to deal with the thread next time I pull the plugs

Steve