Technical Spark plug cross threaded what next?

[dumbledore]

Tried to replace my spark plugs on my new Punto. Replaced 3 OK but the fourth one felt far to stiff and did not attempt to remove. I expect the previous owner has cross threaded it. The old spark plugs seem to be OK so I can drive the car for a while but what can I do next.

 

[ST60SX]

Well at some point it has to come out...

If it is indeed cross threaded, it is sometimes possible to make a good thread with a spark plug with a slot cut out of it. This acts like a tap but with much less swarf being generated.

If that doesn't work it will have to be tapped and helicoiled, but some garages might be reluctant to do this with the head still on.

 

[bredsticz]

The plugs can sometimes be VERY tight in there! Just give it a bit more!
But be prepared incase it is crossthreaded

 

[dumbledore]

The plugs can sometimes be VERY tight in there! Just give it a bit more!
But be prepared incase it is crossthreaded

I tried gently quite a few times and probably managed to move it by almost 45 degrees before it went stiffer. I just tried it again reading this but still the same. I shall leave it for another 10K miles before being more forceful. I fear that if tried harder the spark plug may shear in there and then the head has to come off. Not quite prepared to do this yet.

 

[DaveMcT]

Bad idea, it will be even more seized by then and then the head will certainly have to come off.

Take it to a GOOD garage or machine shop and get the plug removed and helicoiled. Try it yourself and you risk snapping the plug.

 

[dumbledore]

Bad idea, it will be even more seized by then and then the head will certainly have to come off.

Take it to a GOOD garage or machine shop and get the plug removed and helicoiled. Try it yourself and you risk snapping the plug.

I am still trying to sort out my new punto as there are other problems left to fix. Once done I shall revisited this for sure.

 

[DaveMcT]

Unless you have the experience this is deffo best left to an expert. If you dont leave it too long, they should be able to remove the plug and repair the thread without taking the cylinder head off.

 

[Lozzy08]

Don't risk doing it yourself. I had a spark plug brake on me once and the ceramic went into the cylinder. I though I had it all out with a hoover but must have missed a bit and ruined the cylinder. DO NOT TRY IT. It really isn't worth the trouble it might cause, speaking from experience. As suggested take it to a garage/machine shop.

 

[dumbledore]

I am not ready to remove the cylinder head, so yes I shall not attempt to remove the plug yet. Also can't see how an expert can warranty he can remove the spark plug without snapping it. If this happens they will have to remove the head and then it will be a costly job for me.

 

[dumbledore]

I am still thinking about this. I find it difficult to believe that cross threaded spark plug will provide so much resistance once I managed to move it a bit. (45 degrees). Usually cross threaded spark plug hole destroys the thread and then the spark plug actually get looser. I am tempted to believe that that spark plug hole may already have been repaired in the past and that when I try to remove the spark plug I actually try to remove an insert of some sort and that the plug itself is seizes into the insert. If this is the case then forcing it out may cause even more damage.

 

[Tony123]

run the engine so it is hot, this should make it a little looser, if im right in thinking that the hole will expand when hot. and get a long arm wrench see how you get on with that

 

[DaveMcT]

The expert has skills and experience so less likely to break the spark plug. But if the worst comes to the worst the head will have to come off. Using an experts gives you a better chance that wont be necessary.

Another bad idea with leaving the plug in the engine - if the threads strip the plug can be blown out of the engine. It will go like a bullet and almost certainly dent the bonnet. Doesn't bear thinking about if you happen to be looking at it when it goes.

 

[dumbledore]

Another bad idea with leaving the plug in the engine - if the threads strip the plug can be blown out of the engine. It will go like a bullet and almost certainly dent the bonnet. Doesn't bear thinking about if you happen to be looking at it when it goes.

I have this happen to me on another car and I know what you mean. That one was a definite cross threaded but the spark was moving easily in and out. I this case the spark is very tight in there, I will be actually happy if it came out like this.

 

[chase]

Try putting loads of WD40 around the spark plug even for days . Then try working the plug backwards and forwards to see if it will come out . I like you think there is not too much to lose . At least its straight forward , the plug comes out or not !!!

 

[DaveMcT]

Diesel (fuel) oil evaporates less than WD40 but will still soak into the threads. Worth a try.

 

[shaun200765]

Some very good advice on here guys

I'd definitely second the idea of soaking the plug thread for as long as you can and then turning the plug forwards and backwards over and over until it (hopefully) comes out.

Once your there with removing them all its another good idea to use a dab of copper grease on the threads before you pop them back in again.

Another thread on here has been given some brilliant advice from a member (sorry, cant remember who you are) about using a short length of fuel pipe slipped onto the end of your new spark plug to make sure that it never cross threads as you screw it back into the head.

Also, once its finger tight, just an eighth to a quarter of a turn further with the ratchet will be enough.

Good luck mate

 

[DaveMcT]

This is going to need a helicoil or insert because the old thread will either strip or go crossed again. Fitting the coil is a professional job, but a good pro should be able to do it without taking the head off the engine.

I'd say get it to a pro, because even if you do manage to get the plug out you cant drive the car with a missing spark plug.

 

[MikeSalt]

Does anyone know how far the plug's threads protrude into the combustion chamber? It could just be an accumulation of filth on the protruding threads, which would explain why initially loosening was easy, but then it tightened up.

Just a thought.

 

[DaveMcT]

The plug thread should not protrude at all or be sunk inside the head. If it sticks out it will overheat and cause pre-iginiton if its socketed it wont properly ignite the mixture. If it really sticks out the piston could hit it - unlikely but possible with some very long nosed plugs.

 

[dumbledore]

As I said before my feeling at the moment is that the plug may already been helicoiled. The spark is possible seized into the helicoil. What I managed to move a bit may be the helocoil itself. If I force it I will damage the helicoil outside thread and then there is even more trouble. I will wait until I am happy with the rest of the car. There seems to be a lot of little issues with it so not really happy having to become an expert so quickly in fixing this Punto.