Hey guys...I did something really stupid today and I think I cross threaded the head when screwing in a new spark plug. I was able to start it by hand then, when I started turning it with a rachet, there was quite a bit of resistance after 2 of 3 turns. I immediately stopped and the plug looks like it's at a funny angle. The weird thing is I really don't see any "fresh" metal on the female side like you normally do when you cross thread. Anyone know what's involved to re-tap the head? I stopped by a local shop and the guy there only works on domestics but said, and I quote, "you're f@%ked". I'm really frustrated as this is my winter car and I was planning on putting the Mustang away this weekend.

 

Good, Some people don't know when to stop. I'll presume this is the 240 you're working on.
The angle of the plugs in the head is confusing to the eye anyway. There are two plug thread sizes, after that is length is the only difference.
Get an old plug and grind a groove down the length of the threads (with corner of grinding wheel or Dremel, top to bottom) in 2 or 3 spots. You're making a tap. Then chase the threads with a wire wheel or brush or thread file to take the burrs off the ground grooves.
Add some brake cleaner or carb cleaner to the plug hole to loosen the crud and to act as a lubricant.

Add a short length of hose to the top of the plug and go at it by hand.
I've had to eyeball the plug on either side to get the angle straight in my head and eyes at times.
You could spend $18 on the 2 sided tool at the auto parts store.
Luck to you,
ED7

 

My biggest concern with re-tapping is won't that make the hole a little bigger with the possibility if the spark plug popping out? Also, I'm a little leary of doing that myself. I've been looking at the helicoil spark plug repair kit as another option. This really all depends on how much I get quoted when I call the shop tomorrow.

 

Dear brianb:
If you decide to do it your self after all:
My experience with problem threads in aluminum heads. What I have done was use a thread chaser from Snap On tools other makes may just as good but I got this tool. I use aluminum tap and die cutting fluid. The fluid is especially made to be used with aluminum. I use a homemade spring thread cleaner best described as a loop of wire with two ends. The two ends go into the threaded hole the ends have bent pointed tips that go into the root of the thread cleaning out what ever. I have used a shotgun clean brush with solvents cleaning the sparkplug hole. As to the tool not yet for often just doing this has made the threads serviceable but if not I go to the thread chaser tool. I gently try to find the original thread by feeling for it then use as little force as possible to turn the tool into the thread often going back and forth then taking the tool out now and then cleaning and relubricating the tool before reinserting it to try again. I have yet to have to use an insert to salvage an engine. I never work on a hot engine doing spark plugs. I always clean as much dirt away from the plug area with compressed air as possible, before getting at it. The removal of tools and cleaning them before putting them back in the sparkplug hole helps to keep dirt out of the combustion chamber. What I have done is run the shotgun cleaning brush into spark plug holes before trouble and used anti-seize compounds.
Good luck with what ever way you decide to go.

 

Thanx Keith. I just got off the phone with the local shop and they will retap or, if neccessary, put in an insert for about $100. I'd much rather pay that then to have to pay for a new head if I screw the re-tap up. Lesson learned, be very careful when installing new plugs.

 

On any engine, it's always best to seat the plugs by hand...period.

 

The shop was able to use a chase and fix it without having to use an insert. I'm $100 poorer (plus another $68 for towing) but, lesson learned. Swift is right, turn by hand only!

 

If you decide to do it yourself, before anything, use a chase threader, dont tap it. I did the same thing to my car and cross threaded it 90% of the way in. A cross threader is better because it is actually a little smaller than a tap and will just straighten out the threads where they cross. A tap is bigger and will create new threads and possibly destroy any possibility of fixing the head ever. There is another tool out there (forget name) that can reverse thread chase. It splits in half and you can insert the halves into the block and then it will pop back together. that way you have clean threads to start the chase on. It is a bit expensive, around 40-80$ for a very simple tool. I just did it from the outside and was very very careful.

 

About making threads serviceable again, good advice about using a tap on cross threaded problems. There are different classes of fit for taps and dies unless you know what you are doing the thread chaser sounds the best. The special chaser that is mentioned by mikkowus sounds like a wonderful tool but I have not seen it up here in Ottawa Canada that does not mean it does not exist but is not seen in the shops I have been in.Thank you mikkowus.