tapping a alumnum head (spark plug)

[mostwanted]

My wifes car has some buggered up threads in the spark plug hole. Appearantly it is a common problem. Anyhow, I bought a tap to attempt to chase the threads. I tried to start it, but it's not going to be easy. I was curious if a thread chaser might have threads to start as the tap is wanting to cut new threads. Or should I take the head off and start from the bottom up? I am relativly new to this type of repair, but I am convinced I can do it. Worse case I may have to take the head to a machinest to have a heli coil installed. What are your thoughts?

 

[DEMON44]

Helicoil insert will be the most effective repair.

 

[mostwanted]

I wound up chasing the threads with a tap. It appears that the damaged threads were closest to the top. The spark plug is now in and car is running again.

 

[Confedneck79K30]

4.6?

they have a lot of problems, and there's a guide with a reamer and a new tap with thread inserts, that plus a little 2 part works like a champ

 

[sled_dog]

4.6?

they have a lot of problems, and there's a guide with a reamer and a new tap with thread inserts, that plus a little 2 part works like a champ

If it is a 4.6 or a 5.4, I'd check the spark plug often to make sure its not loosening up. They are really known for getting loose and blowing themselves out, taking half of the threads in the head with them.

 

[chevyin]

Screwing a steel spark plug into an aluminum thread will result in a phenominon called electrolysis, unless anti-siez is applied. In the early days of aluminum heads, it was not uncommon to try to change your plugs for the second time (having forgot to use anti-siez) and have the aluminum threads from the heads to come out with the plugs. I thought all aluminum heads now came with steel inserts in them. IMHO, if you have a head without inserts, install Heli-Coils. This will solve not only the thread problem, but also the "loosening up" problem that Sled Dog rightly brings up.

Also, Heli-Coil installation kits are available at all good auto parts stores. The kit includes everything you need, including the drill bit, special tap, coil installation tool, and coils.

 

[DEMON44]

its called Galvanic Corrosion when 2 dissimilar metals come in contact with each other with an electrolyte. Even a mild solution of snow and road salt is more than enough.

 

[mostwanted]

It's a '96 Pontiac Sunfire. So far so good. Drove it over 100 miles in the last 2 days. We are working on another human addition to our family (its a boy), so we have needed the car. Anyhow no problems yet. But for mechanical discussion's sake, let's keek this thread alive.

I have heard that heli coils will come out over time (unless there's some trick to intalling them that I am not aware of). If the threaded steel insert was bonded on pinned into the alumn. then that would make a good mechanical bond.