If I had to cope with this (instead of returning the car and asking for a proper one) I would reason that the original plug's thread might have been damaged at the bottom end at the same time that the internal thread in the head was being damaged at the top end.
I would obtain a new plug, smear the threads with copper ease or something of the sort, and insert it straight. If the engine problems resulted from a poor seal with the original plug this might cure it. But I would only be 75 per cent optimistic.
|
|
|
To expand upon oilrag's delightfully concise answer - which I tend to agree with;
The proportion of heat that passes via the spark plug threads depends upon whether you have a hot or a cold plug to begin with. If you have a plug that is towards the hot end of the spectrum, there's no direct connection between the hot central electrode & insulator and the thread area, and the detail of the thread will make no difference to the operating temperature of the plug. On the other hand, a cold plug has a direct connection to the thread area, and more heat passes via this path - possibly up to 40% of the total heat. The helicoil would introduce an extra interface and there would be an extra thermal resistance because of the extra discontinuity.
If I were faced with this situation, I would fit a helicoil and a set of platinum electrode plugs - they have a broader heat range than standard plugs.
Number_Cruncher
|
|
This car would have platinum plugs in anyway-should have a P or PP in the plug number.
|
|
Just realized that no-one ever said what car/engine-got the impression somewhere that it was a late KA.
|
>>Just realized...
Until you said that, I was in awe of your powers!
;-)
Number_Cruncher
|
I have very rarely found a previously untouched bolt to rip the thread when undoing for the first time. I assumed it must have been caused by some dirt when originally assembled, or else a small machining flaw causing a hot spot when tightening.
I think the golden rule with spark plugs is to be very cautious the moment you become unable to turn them with fingers alone. At that point it is worth squirting in lubricant, and then working it backwards and forwards, each time trying to extend the range over which it moves freely. If you just go blindly on, whether screwing or unscrewing, then it can get intensely hot and I think cause localised welding and then ripping.
|
|
