Spark plug threads

[Roadster90]

what is out plug thread please....14 or 18 mm ?

[Roadster90]

No one knows the thread mm per inch (I am guessing that it is measured by the inch or some metric figure)....it may be neither of the two....I was thinking about buying a thread chaser and just need to know the number of TPI

[Ronnie]

Is this what you are looking for?

[Roadster90]

Thanks Ronnie...thought no one would ever answer...that is the tool, but I have located a combo with both 18 and 14 mm on sale at Harbor Freight for 3.95 with coupon....I just was hopeing to make sure that 14mm is the size of the plug that fits the Reatta.

[Ronnie]

You're welcome Nic. A word of advice from a machinist (me). Don't go to cheap on a tap. Cheap ones get dull really quick and will not cut a thread smooth which could result in the spark plug being hard to remove. Greenfield and Vermont are the top Brands. Do some research on other brands you decide to buy.

Also, if you are going to run the tap into a spark plug hole that is on the engine, put heavy grease on the tap to catch any metal chips that might go into the cylinder. Only run it into the hole a little way (two or three turns) and remove. Clean the metal chips and grease off the tap and hole, re-grease the tap and do it again. Repeat until the hole is re-tapped all the way. Carefully clean the hole before using.

[Guest Mike_s]

I think KD and Leslie (sp?) both make spark plug thread chasers which are probably available at a local parts house.

Even sears might have them in stock

http://www.sears.com/shc/s/p_10153_12605_00999910000P?vName=Tools&cName=MechanicsTools&sName=Automotive%20Specialty%20Tools&psid=FROOGLE01&sid=IDx20070921x00003a

[Roadster90]

This one is made by Pittsburg Tools and looks decent, but it is combination -two different sizes - one on eache end.

And I am still in suspense from the original question ....is the Reatta plug threads 14 mm please?

I can borrow a metric thread gauge, but will have to go downtown to do so....

[Guest Mike_s]

Nic

I'd pass on the Pittsburg tool for this application, taps are hard so they can cut, but that can make them brittle and succeptable to breaking, to me it's not worth maybe saving $2-5 only to risk a royal Pain if it breaks and gets stuck in the head, or mucks up the head threads. That, and what Ronnie said

As far as the spark plug size, sparplugs.com gives info your looking for, move the cursor over any plug and it will tell you the dimensions

http://www.sparkplugs.com/results_app.asp?productTypeID=1&AAIA=1019898

my 88 came up with a 14mm, but you shoud check on your own

[Ronnie]

I'm not aware of any GM vehicles that used 18mm plugs. At least since 1955. Maybe some of the early antiques used them. Only thing I remember using them is 1960s and earlier model Fords.

I would not base my tap purchase on it having a tap for 18mm plugs. Get yourself a good name brand tap and you can't go wrong.

Bad tools are like bad women... they will let you down as soon as you start to depend on them.

[Roadster90]

OK guys-will pass on the Pittsburg....but, is it still a good idea to chase threads when replacing plugs, or am just trying to create more problems than I had to begin with? I have a heck of a time removeing (breaking loose the plugs to remove - especially the rear ones). I generally have to break the things....never seen anything like it - AND as I stated before, I always use anti sieze compound???

Thanks,

Nic

[Guest MauiWowee]

Nic, I'm not too sure how wise it is to always chase spark plug threads. The only time I have done it was because some bone head cross threaded a plug. Most of the difficulty in removing plugs comes from the different metals involved, ie. aluminum and steel. I haven't had too many problems since I started using anti-seize. Of course it doesn't help that the rear bank of plugs on our cars can be a ballbuster to get to.

I would think that you might run more of a risk of damaging spark plug threads by regular chasing. IMHO

[Guest Mike_s]

Nic,

What brand and type of anti-seize do you use?

Some are made with aluminum, and\or copper, and\or,nickel, I myself have wondered which is the better to use on the reatta. The most appropriate anti-seize seems to depend upon the metals being joined, which in this case is the plugs and the cylinder head.

Here's some relatve links

http://www.permatex.com/products/Automotive/lubricants/specialty_lubricants.htm

http://www.advrider.com/forums/showthread.php?t=212510

If anyone's got advice on anti-seize i'd like to hear it.

sorry for the tread hijack Nic

[Roadster90]

Hey not a problem Mike....very revelant.

I was or used to use some that was silverish looking....I have got some now that must be copper based as it is copper colored. I will look at the links....Interesting and could very well be very important...thanks

Nic

[Vincent Vega]

If the plugs go in smooth and easy why chase the threads? The plugs should last 30k or better. How often do you replace them?

[Roadster90]

Craig, Just trying to figure out why the plugs are so VERY difficult coming out....originaly at the beginning of this post my thoughts were that there could be residue of some sort remaining in the threads in the head that could possibly be cleaned out to eliminate that difficulty....discussion is proving those thoughts not a good idea.

[Guest Squire Tom]

if the heads or block is aluminum and the spark plugs are a form of iron ,or if the chemistry of the heads and threads is dissimilar enough , there is a phenomenon in metallurgy called diffusion bonding. it requires temperature time and close contact between dissimilar metals . guess what !

spark plugs meet all of the above.

good idea every 5 k or so to loosen and tighten plugs , only takes a few minutes . quarter turn loosen and tighten is enough to keep the bond from becoming too strong.

hate to see what happens with those 100k plugs.