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Spark Plug Breaking At The Thread


PearlLex
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I have heard of this with cast iron blocks and aluminum threaded plugs. I have also heard of this (I did it) when trying to take out a spark plug without using a spark plug socket (just used a regular socket) and it wasn't on straight.

it is a nightmare to get the old plug out, but is doable.

The hard part is keeping debris and metal fragments from dropping into the cylinder when the damaged spark plug is finally removed.

steviej

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I have heard of this with cast iron blocks and aluminum threaded plugs.

I never saw aluminum threaded spark plugs?? I always thought the threaded portion of a plug was made out of steel. :blink:

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it happens when a hot plug is taken out of a hot engine especially aluminum, it happens when the head is still hot and expands with no plug in there , so when the plug is reinserted it is very hard if at all thus heating the head again cuases it to cross thread and seize.

did this happen to you or is it a hypothetical situation ?

If so which plug?

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When you get it fixed & install new plugs, make sure you put some anti-seize compound on the threads before installing the new plugs......this should make things easier to remove the plugs again down the road when performing a tune up & like steviej mantioned, use the correct tools as well.

:cheers:

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sorry, Alan, I meant to say cast iron blocks and aluminum heads. I had spark plugs on the brain.

In reference to spark plugs, I have only seen steel ones too. The gaskets, however, are occasionally aluminun.

My father was telling me about some trucks that he has worked on where they went to take out the plugs (which had never been changed), applied the proper wrench/socket and the plug inerds and shank all came out but the threads stayed in the head. This was about the advent of anit-seize.

steviej

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SK-

you don't use anti seize on spark plugs it is for bolts not electrical transfer joints which would become baked under current and no longer be anti seize but a sure seize'

I don't know why you said that! I have used high temperature anti-seize compounds for many years (probably before you were born), when installing spark plugs on my cars, boats, etc. This type of product worked very well on aluminum or iron cylinder heads with absolutely NO problems.

Anti Seize

Also, read what one of your fellow Canadians said about installing spark plugs.

Installing Spark Plugs

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SK-
you don't use anti seize on spark plugs it is for bolts not electrical transfer joints which would become baked under current and no longer be anti seize but a sure seize'

I don't know why you said that! I have used high temperature anti-seize compounds for many years (probably before you were born), when installing spark plugs on my cars, boats, etc. This type of product worked very well on aluminum or iron cylinder heads with absolutely NO problems.

as have I, my father (who taught automechanics for 33 years), my brother and every other mechanic I know.

I also use dielectric grease in the spark plug boot.

steviej

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If the plug is easy to get to then it can be done with an "easy-out" and without removing the head. The easy-out grabs hold of the inside of the plug, and bites in. The easy-out rotates in the opposite direction of the threads so once the bit takes hold, the threaded part of the plug unscrews right out of the hole.

I think Pearls stuck plug was the middle on the rear cylinder bank. That's kinda tricky to get at, so you may be right.

steviej

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I guess you know more then the experts. :chairshot:

i believe general motors does not recommend using antiseize on spark plugs and i have seen other sources that also do not recommend using antiseize.

the main concern with antiseize is not that it would be a 'sure seize' which i do not believe but have not looked into it that much... it's that antiseize is still a lubricant of sorts and the danger is that it will cause overtorquing of the plug that will cause just as much damage.

taking it one step further, the concern is that joe-servicetech working on his ump-teenth car of the day uses the antiseize on the plug and then threads it in with his rachet and gives it a final 'umph' to tighten it to spec by his 'feel-o-meter' to in reality about 20+ lbs of torque.

that being said, i just installed new plugs in my z06 when i installed headers and used a dab of antiseize on the plugs. i used a torque wrench and carefully torqued to factory spec and am comfortable with it. as a diy'er, i trust i am careful with torquing and i am more concerned with galling by not using the antiseize and destroying the threads on the head.

don

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i believe general motors does not recommend using antiseize on spark plugs and i have seen other sources that also do not recommend using antiseize.

GM typically uses plugs that don't come with metal ring gaskets like the plugs Toyota uses. Instead, GM typically uses tapered thread spark plugs which seal themselves without use of a metal ring gasket. So that may be the reason GM disapproves of the use of anti-seize.

I've been using anti-seize for 18 years in a wide variety of Toyotas. Never any problems.

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