2.4 spark plug insert

I have a 2.4 mk2, I have a problem with the spark plug from no2 cylinder,when i removed it the insert came with it and I can not remove the plug from the insert.
Can any body inform me what thread is used in the head for the insert to go into.
I would like to try and find a correct replacement if possible instead of going down the route of re threading.The head is still in the car.

Welcome Martin. You have selected the best forum for this question.
Cylinder heads do not normally have threaded inserts for the spark plugs.
It seems likely that some previous owner or shop installed that insert because of damaged threads in the head.
You may be able to remove it from the old plug and reinstall it in the head, depending on what damage there was initially and what damage is new from removing it.
There are several types of inserts on the market, with their own installation methods, so you should probably take it to a auto parts store and get them to identify it before you proceed further.

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A tool worth getting is a thread chaser I had a tight spark plug , got a thread chaser , put some grease around it and run it down the plug hole a few times , no more tight plug !

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Hi Martin, and Welcome.

I’d think a decent Ace Hardware or fastener store could look at the plug with the insert attached and tell you what the threads are.

If you have a Lowes near you they stock thread gauges. A thread gauge is quite handy to have.

If you have not parted them yet , put the nut part of the spark plug in a vice , then a pair of Stilsons on the insert

A Stilson is a monkey wrench…or pipe wrench?

In the UK Stilsons :slightly_smiling_face:

Thanks for the suggestions on this post I am going to add some photos to illustrate the plug and insert it is inn, also a standard plug and insert which is M16 x1.25 thread.
I think the insert from my head could be imperial thread.
Thanks for your input.


The original insert is better than the new one. The new one seems a bit short. I would soak the old plug in a penetrating fluid for a day then dry it and apply a bit of heat. You need to protect the thread so use pliers or the like with rubber or plastic between them and the insert with the plug in a vise and keep trying. Also freeze spray into the centre of the plug may help.

If you are not fussed about keeping the plug cut or grind the washer out to relieve any tightness at that point.

When you do get it out loctite it back into the head with a heat rated loctite.

Good luck.


Are you sure it’s not a 14MM?

Hi Gents
I give an update on my spark plug insert problem,it turns out the thread size is M16x1.25. I bought 2 M16x1.25 nuts,then I put them on the insert, applied some heat and managed to remove the plug.
On further investigation it seems some contamination had got into the threads on the inside of the insert,this is what got the plug stuck in the first place.
I am now going to clean it up and reuse it and put in into the head using high temp loctite.
Again thanks for your support on this matter.

To answer Lee’s question, the thread on the plug itself is 14mm x 1.25 mm/thd.
see page 27 for threads, page 30 for torques.

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The outer thread of the insert is 16mm, then…gotcha.