Welding into spark plug threads

[cardiffrob]

Just a quickie...I need to weld a waterway in an alloy head that is right through to the extended plug hole. If I got a piece of copper rod and cut a plug thread onto it and left it in the plug hole, would the ali welding be easier due to the forming of a new bit of ali thread or would I be better off welding through and then re-cutting the hole and threads?
I seem to recall someone mentioning this concept before but am not sure if it was Tig on Ali or something else.
Thanks
Rob

 

[Windy Miller]

I've seen a similar thing done with a lightly tapered steel bar in an ally hole once, but copper may also work. Not sure really. Either way you'd want to unscrew it pretty quick before it cooled and grabbed the bar!

I'm wondering if would be a good idea to helicoil it afterwards?

 

[cardiffrob]

I did also wonder about going for a smaller diameter plug. NGK make some cpr6e plugs in 10mm so I'd gain an extra 2mm of wall thickness. It would mean making a thin walled sleeve.

Still undecided as to the best way to proceed with this job.

 

[RichardM]

what about a wurth plug insert

 

[cardiffrob]

Not enough meat in the head to get one in. The plug thread is just a few mm from the head gasket. Here is a head with corrosion in a similar spot at the bottom right corner but mine is deeper.

 

[RichardM]

10mm plugs are 1.00mm pitch, 12mm plugs are 1.25mm pitch - same as 14mm