Cross threaded spark plug - CharlieG
Can anyone help? I have a 1992 Astra and have found that a spark plug (second from distributor cap) has been cross threaded. The car appears to run fine because it was not until yesterday I found this out when I went to change the plugs. The plug in question goes in about two thirds of the way before coming to a stop. I don\'t want to force it in case I do more damage. My questions are:

a) Could it keep running without problems for some time (it does not seem to have affected it so far)

b) Is there an alternative to having the cylinder head reconditioned? (if not, then I\'m going to trade it in because it\'s worth less than the cost of the work). I was think along the lines of the way a tap & die is used in similar circumstances, but not sure if it can be done with a car.

Any help/suggestions greatly appreciated.
Cross threaded spark plug - jc
Look in the "Yellow pages" for an engine reconditioning firm;they will either be able to recut the thread or fit a Helicoil without removing the head.
Cross threaded spark plug - CharlieG
Thanks for this info. I'll check this out in case I bodge up DD & Sean's suggestion
Cross threaded spark plug - Dynamic Dave
There is a previous thread (pardon pun) lurking somewhere regarding Ford Ka plugs. It mentions cutting a groove into the thread of an old spark plug and using that to screw down into the spark plug hole to clean out/recut the thread in the cylinder head. If I can find it, I'll post it later.

If you leave it as it is, what will eventually happen is that the remaining threads in the hole will clog up with carbon, as the plug hasn't been screwed in all the way home.
Cross threaded spark plug - Dynamic Dave
Further to my earlier note, I forgot to mention removing any swarf from the plug hole afterwards. This can be done using a small rubber tube attached \"Heath Robinson\" style to your domestic hoover and poke the tube down the plug hole to suck out any swarf.

No luck in finding the thread I mentioned earlier, sorry.
Cross threaded spark plug - CharlieG
Thanks for this, seems that all is not lost. I had visions of having to scrap the car
Cross threaded spark plug - sean
I would either use DD\'s tip about hacksawing some grooves in an old plug and gently inserting it into the hole. (get to the point of resistance then go half turn fwds, half turn backwards, until you get to the base. Personally I\'d attack the old plug first and break off all the ceramic, leaving you with a nicely threaded stub to use.


You could buy a tap of the right size. Sealey do one. Suggest a local factor, or even Halfords.

If it all goes horribly wrong, don\'t worry you can have the hole drilled oversize and a helicoil insert fitted.

Hope this helps you.
Cross threaded spark plug - CharlieG

Ta! with your's & DD's tips, I now can see there is some hope. Now all I need is the guts to start!!
Cross threaded spark plug - sean
I want you to come back here and tell us you did a job you're proud of. Don't worry, it's not a hard job BUT TAKE YOUR TIME.

Get an old plug which fits the hole.

Stick it in a vice (not on the thread) and hammer out the insulator.

Get a hacksaw and cut a couple (1 then another 180 deg away) of diagonal saw cuts. Go to a depth of about 1mm. Ideally angle it so that a channel will take debris UP as you screw it in.

Go slowly and gently, a bit at a time. Get some cutting oil, or light machine oil.

Remember the plug's steel and the head's alloy so be gentle.
If it gets stiff take plug out, clean threads and the channels you cut, then go again

You really will be pleased with yourself. Good luck mate.
Cross threaded spark plug - David Lacey
A Spark Plug thread chaser is what you want......available at Halfords I think..
Cross threaded spark plug - Railroad
You can buy a 14mm spark plug tap at just about any tool shop. They're very easy to use and should do the job perfectly well.
Cross threaded spark plug - Mark (RLBS)
Just be a little careful in that it is almost as easy to reinforce the crossed thread as it is to restore the original.
Cross threaded spark plug - madf
one tip if you are going to use the old spark plug with grooves cut in it is to smear all the threads and the grovve with coppaslip (or grease). This will reduce friction and retain swarf in the grease in the groove. Remove regularly and clean and regrease...
Cross threaded spark plug - CharlieG
Thanks to all that have given me the valuable advice. I am going away for 3 weeks and have the time to consider whether I am brave enough to try to repair myself or take it to an engine remanufacturer. I have spoken to one who is a memeber of FER and can fit a helicoil in situ for £40-50. Have checked them out via FER and have been told that no bad reports received. Watch this space, but the way my luck is going at the moment (over the weekend apart from finding this out,my wife's iron blew up, bathroom almost flooded and wife burnt herself) I may bottle out of this and pay the man to do it....
Cross threaded spark plug - Dizzy {P}
Better to go to someone who's a member of the FER than someone who's not ... but I wouldn't expect the FER to tell you if they *had* received any bad reports about one of their members! Almost like trying to get acknowledgement of a bad solicitor from the Law Society! Well, perhaps not quite that unlikely ... but you know what I mean.

You may decide that £50 is better in your pocket than in someone else's and to have a go at the job yourself. If so, and you make a hash of it, the helicoil will still be able to be fitted as it requires drilling out of the old thread anyway.
Cross threaded spark plug - Hugo {P}

Would you have to remove the cylinder head to re tap the thread to stop swarf from entering the cylinder?

Having seen examples of what can happen when an oil ring gets blocked, I think you would.

In which case, Charlie has the added expense of this to think about.

Cross threaded spark plug - Cliff Pope
I think the swarf risk is a bit overstated. If you catch what you can on the greasy tapper, and then use the hoover dodge to clean out the combustion chamber, that should get virtually all. Even if some is missed, my bet is that it will be blown out down the exhaust pipe in the first few seconds of running.
Cross threaded spark plug - Dizzy {P}
I agree with Cliff that removal of the head isn't vital in this particular instance. The odd bit of aluminium swarf that escapes shouldn't do any measurable harm. The car is of little value anyway so it really isn't worth going to a lot of trouble and expense simply to avoid a small risk of swarf damage.

Ask Honest John

Value my car