Spark plug inserts

My no.4 spark plug has at some point been cross-threaded and rethreaded by a previous owner. The plug has been stuck in there since I got the van, but recently I got it out, along with the insert.

The problem is that I can't find a new insert that matches the size. The old one (fused to the plug) has a major diameter of 15mm, as best I can gauge. I tried a good Heli-Coil Sav-a-Thread and the EMPI ones from the usual sources, but they are all 16mm or greater (not that they tell you this anywhere). I'm avoiding the usual junk on Amazon, since this actually matters.

Anybody know of a quality spark plug insert that fits an M15 pre-tapped hole? 3/8" reach.

 

Is it a helicoil or a solid insert? The plug thread is M14 x 1.25, but I’ve no idea what the external thread of the helicoil would be.

I wouldn’t put money on you being able to insert a new helicoil without taking the head off. I’d doubt if screwing it in with the plug will work. Generally, solid inserts are better for plugs.

 

PS The kits from Machine Mart are fine.

 

I use V Coil solid inserts. They come as a kit with a tapered tap that opens the head thread out to 16mm to take the insert. Its a head off job though..

 

The old one looks to be a solid, though it is a bit gnarly now. The ones I have tried are solid inserts, including the Heli-Coil brand one. Shouldn't use coil types in this context, I'm pretty sure.

I'm trying to avoid re-tapping the hole, and I shouldn't have to, since the thread is fine. I just want to find a decent insert that will fit, then I can install it properly.

No idea why the companies that make them don't give the tap diameter, even in the datasheets.

 

Do you know if they are 15mm tap?

 

No idea.

My Sealy solid insert kit uses an M16 x 1.25 tap to widen the hole out. It will likely put swarf into the cylinder if you do it in-situ, though.

 

Check out time-serts

 

I've found the coils are fine, but not for plugs. If they get hot and corrode, they can come out with the plug.

 

That is looking most likely. They are about the right size. Spendy though.

 

Take a look over on the Samba.

Suggestions include using some copperslip type stuff on the spark plug thread trying to get it to stop binding.
And with some inserts it seems to be possible to spread them out a bit inside the combustion chamber so they are less likely to come out with the plug.

 

Superspares in Balham still has a few Time-Serts in stock. Fingers crossed that'll fit.