I have a stock head with motorcraft plugs. I am get some gas leeking around threads on the plugs. Is this a problem? Is this normal?

This is caused by the threads being worn. I have been able to successfully fix this by wraping aluminum foil around the plug before inserting it into the head.
Norm

Tim,
A leek around the plug is not normal. The spark plug holes are a pipe thread, they are tapered so the deeper you go the tighter they get. Your Motorcraft plugs may be the problem, try a Champion X and see if that solves the leek.

Tim, I have a T that has some thread wear.Most do. Champion 25s' seem to leak less in this engine than Autolite or Motorcraft. I don't think a slight leakage is a big deal.I use all of the above plugs with good service.The ultimate,though,are original Champions if you can find a good set.

I used a couple of wraps of Teflon tape on the spark plugs. Worked good for me. Dave

Plumbers tape worked well for me.

Vince M

Thanks I am new to T's. I have a set of newer Champion X so I will give this a try.

Teflon tape works good for me too.

Neil

I pulled the Champion in took the car for a spin and I see no blow by. Thanks Tim

Gotta check the new re-pro Champion plugs..... check for sharp threads. If they're flat , no sharp cut, the plug will leak compression. This goes for any other brand of plug also.

I sent back a new Champion set, complained & received a set with sharp threads...... no leaks .


Bob Jablonski

Wear & tear over the years. Buy or borrow a 1/2" NPT tap, load the flutes with grease, and gently run it down the plug holes until it snugs up, but not too far....The grease should catch any shavings for you.

If you have the blowby, you might not be able to "see" it, but when you are pulling hard, such as uphill, you will hear it.
Norm

This comes up every so often. It's caused by malformed threads on the new plugs. Unless the threads form a nice sharp "V" you'll get leaks. You can use any of the sealing schemes above. Most of the time the leak is not large and poses no problem but can make a small mess. Don't just reef down tighter on the plug, especially if you've got an aluminum head.

Yes, it's possible that the threads in the head are to blame but when you mentioned the new plugs I immediately thought of the obvious and common problem of bad plug threads.

Pipe threads need either teflon tape or pipe dope to seal. Plumb a house without using such and you will have leaks even if you are using fresh cut threads. I agree with the tape suggestion and also offer permatex on the threads will correct the slight leakage you are experiencing.

I don't know the age of the Champion X plugs but they are over ten years old and they are the take apart kind. Being pipe thread I do worry about over tighting the plug.

Military pipe thread tape was suggested to me and works perfect, here is a link to mc mastercarr below.

http://www.mcmaster.com/#military-specification-pipe-thread-tape/=298rlb

Barry suggested getting a 1/2" NPT tap. Since these come in various threads, what is the TPI please?

William Cuddy

William, try this link it should provide the information you need as to threads per inch.
MarkG
http://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html

14 TPI

Seth

William -- The threads are pipe threads, not bolt threads. There is only one standard 1/2" pipe thread.

There are different classes of pipe threads. NPT found on black iron or steel pipe does not have the sharp crest or root on the threads so without a sealer it will have a spiral leak. NPTF. "F" for fuel threads have a sharp crest and root on the threads and as the threads are tightened the crest and root make contact first. as the threads are tightened the crest crushes slightly completely filling the spiral gap and as tightened further the sides of the threads make contact and the seal is complete. These NPTF threads are also called "dryseal". Re tapping the female thread will not help as others have said,if the spark plug is missing the sharp thread.
Many people are confused regarding pipe thread sizes as on average the thread measures approx 1/4 " larger than the named size. The size refers to the inside diameter of the pipe which the thresd would be on. Therefore the 1/2" pipe thread on our spark plugs measures about 3/4".
Sorry for rambling on. John.

Wouldn't wrapping the threads with tape - whatever kind - be insulating the spark plug from its ground, thereby rendering it inoperative? hmmmmmm?

Wrapping the threads with tape would insulate the spark plug - if the tape stayed intact. But the threads cut and/or rub through the tape to make the electrical connection.

SETH

Thank you for that information. I have ordered a Snap-On 1/2" NPT tap 14 TPI and will give it a go. I will let you know my result. Thank you.

WILLIAM CUDDY

My pleasure, William, as always. You should be in business with that tap. Coat it heavily with grease before chasing the threads in the head and nothing will drop into the cylinders.

Seth