S4

[chiefmechanic]

My 1993 s4 has blown one of the spark plugs out of the head. It looks like it had an insert fitted prior to me buying it. Long story short I wasn't there when it happened as the son was using it as a daily and called out the Aa. Aa man has kept the plug so I don't know what kind of insert was on it. I am buying another but don't know what size to buy. Is it m12 or m14 X 19 long. Standard plugs are fitted. Thanks, Brian.

[hunker7]

I personally would replace head if possible. I used insert and it melted my spark plug eventually.

[chiefmechanic]

Insert

Don't have another head. This one has already been worked on. Ported and polished with a few other mods. Would like to try to fix it. If that's not possible then I'll try another route .

[hunker7]

If you decide to go for thread insert, do take the head off when you do drilling. When I did mine, even with being super careful some metal filings ended up in cylinder and did some damage.

[chiefmechanic]

It's already been drilled for an insert. The Aa bloke took it with him along with the spark plug. I want to replace it but am unsure of the size.

[Error404]

So are you saying that you have already had an insert on the thread and that has blown out too?

[hunker7]

M12 is standard size, m14 is what you drill to have insert, so you'd need M16 now to get new insert again, not sure you have enough space to do so?

[chiefmechanic]

A standard plug is too small for the hole and the sides look machined and devoid of thread. If the standard plug had stripped the thread I would expect the bore to be rough and burnt as opposed to smooth and shiny. I do not have the plug and I was not there when it was recovered. This was done prior to me buying the car 5 years ago.