Yes, you can get 8mm thread Heli-coils or equivalents. Of course, if the £20 head from GF is completely sound, it's cheaper than buying the kit... However, if you ever needed to do it again, you're on to a winner!

Sound advice already given, remove head & either replace or repair.

The stuff about attempting a repair with head on the engine is shocking, but then the seed of this did come from a vicar, so a fair chance you will be bu99ered.... big

I'd swap the heads. Get a spare from Graeme 0- he is a nice guy, doubt that he would try adn sell something not fit for purpose!

That head he has will be bare though at that price? So be ready to get the valve gear out your old head and transplant it to the new one - lapping the valves in too...and shy not remove the casting flash from the ports...

Not the cheapest and fastest..but if you are going to do a job..do it well. right first time and no messing.

CMSMJ1 wrote:I'd swap the heads. Get a spare from Graeme 0- he is a nice guy, doubt that he would try adn sell something not fit for purpose!

Wasn't suggesting he was selling junk, just that the description 'good for spares' has me wondering if he means it's good for stripping bits like springs and valves out of rather than just plonking straight on the engine as it comes?

Its ok swapping heads, it would be the best solution really, but then you'll more than like need shims and other stuff, so it'll prob get quite expensive. I'd just bung a bigger plug in it, heli coil, or time insert see how it goes if you naker it doing that then get another one! I think the nc24 had 10mm plugs in them but i dont know if there the same casting.
You could just try running a tap down it to clean the threads out if the plugs not going all the way in, it maybe just a couple of the start threads thats gone if you put the plug in slightly cross threaded.
Cheers
Ian