Helicoils - Threaded Spark Plug Hole

[JonL]

First off, apologies for a non Nova specific problem!

Right, my daily drive Renault 19 (ugh!) blew out a spark plug the other day, due to the spark plug thread in the head being threaded by the looks of it.

I'm trying to get a helicoil kit for it, but all thats available is an M14 kit as far as i can see, and the spark plugs in the 19 are M10. There's normal M10 kits, but not the spark plug specific one.
As its a 16v head I really need to get the spark plug one as its deep in the middle and I don't want to take the head off if i don't have to.

Am I missing something, is there a reason why they only do M14 kits?

Any other ideas for solutions for this problem?

[Welsh Dan]

I guess they're M14 because you need to drill and tap the hole out to M14, so that you can fit the insert that is M14 externally and M10 internally.

[JonL]

Thanks, Hmmm, i had actually thought that, although I'm worried that if it doesn't work I'll have made the hole much too big to ever fix...

[craig green]

Surely you cant do this in situ? You'll have a combustion chamber full of swarf & a recipe for broken valve guides....

[JonL]

Well, i was worried about this, but I've read a lot of stuff from people who've done it and it seems like if you coat the tap with a load of grease this should catch most of the swarf. After that its just a case of tidying up the tiny bits that are left. Any of the tiny bits of aluminium left shouldn't do any major damage...

[craig green]

Theres hope. Personally I wouldnt tap a hole with a greased tap. Paraffin is the best cutting agent for alloy.

I've never had to do it though, so my comments arent worth a dime tbh.

[draper]

i wouldnt be drilling anything on an engine while its still in situ tbh

[craig green]

Fixed the spark plug......... ruined the engine!

[JonL]

Just found this old thread, just thought I'd add that for anyone that has to do this, I Helicoiled it in situ, and it was fine. Just was very careful about it.