I have a 2004 Mustang GT one of the plugs has blown out of the heads I bought a tap 14mm 1.25 to rethread the head the tap is to small for the strip spark plug hole, so I try the tap on another spark plug hole and the tap is still to small but when I bought plugs for the car I bought for a stock and all plugs fits with no issues. How can I fix this? I bought the tap at O'Reilly's for 10 bucks!

 

http://www.timesert.com/html/ford.html

Fairly common in 2003 Mercury Marauder motors......heads changed in 2004....more threads in spark plug boss!!

Good Luck!!

 

I use TimeSert exclusively. Quality stuff. One of my customers had two holes fail and paid me to do them all in his V10 motorhome. It's the best fix out there.
After performing them for quite some time, I started reaming the hole "dry" and using a 3/8 fuel hose attachment for my shop vac to get the dry shavings out of the cylinder...then blowing it out with compressed air. It's inevitable that some shavings will get into the cylinder and grease just causes the shavings to stick to the piston, making them difficult to remove. I even advertise the spark plug repair service on Craigslist here in KC.

 

A question if I may:
Is this plug blow out issue a natural occurrence or is it caused by someone not properly torquing a replacement set of plugs or non use of anti-seize at some point?

 

My 2002gt had the same thing, and it was fixed with the inserts.
I believe it is a design defect, it's a relatively common failure.

 

The 2003 Marauder motors had 3 threads holding the spark plugs....KINDA LAME IMHO!!

If ya over-torqued 'em or removed 'em HOT you almost always damage these few threads!!

I am guessing some of this crazy manufacturing spilled over into the Mustang arena??

If you're careful the 3 thread heads will do fine but key word here is "careful"!!

Timeserts work GREAT but ain't cheap!!

 

Most I have seen are under-torqued. The V10 I just did had 3 other plugs that were not tight...and it still had the factory plugs in it ay 37k miles.
I'd rather fix one of these than a broken off spark plug in the 3 valve motors. At least with these, there's nothing stuck down in the hole.
4.6, 5.4 and 6.8s were affected depending on year, number of cams, and number of valves.

 

All of the above. In addition to pre-2004 PI heads having only about 4 threads, overtightening leads to fatigue and then eventually game over. Lack of anti-size I could see being a minor contributor, especially if removing plugs on a warm engine.

An above post also suggested undertightening, which also makes sense - if the plug were to back off a little from being snug then it wouldn't take much at all to blow it out the rest of the way.

 

FORD had some poor designs back then but the 3V heads with those LONG spark plugs were the worst!!

 

What mm are the plugs 14?