chasing spark plug threads on head?

[Jer]

I have the head off my 74 (1275) because the #2 would not come out since I got the car just over 2 years ago... penetrating oil did nothing so finally I bit my lip, hooked up the impact (on light setting) & walked the plug out (back & forth) it didn't break off, but the threads on the plug itself had a slight dishing near the middle (I assume PO over torqued or something), I can start a plug into the socket on the head & then it starts to tighten up...
I want to chase the threads on the head - anyone know what tap size I would need?

 

[donbmw]

Can't remember what size. But most auto parts houses have spark plug thread chasers. Usually one that is doubled ended for the two normal size threads.

Don

 

[Bayless]

Do get a thread chaser, not a tap. The chaser will clean and somewhat reshape existing threads with little danger of cutting a whole new thread which could be a disaster. Don't ask how I know this.

 

[Jer]

Thanks for the advice on the chaser, I will get one next time I'm at the auto parts store !

 

[Guest]

It's 14mm but I forget what pitch. Last chase I bought cut like a tap and made the hole too big.

 

[Mickey Richaud]

Pretty sure the pitch should be 1.25.

 

[nomad]

Take in the correct plug and if your parts store is any good they ought to be able to get it right!

Kurt.

 

[Jer]

Got a 14mm/18mm chaser at advanced auto parts last week, past weekend, I tried it out (the 14mm) & worked perfectly, the only debris I seen was dirt, not fresh metal shavings! ran it thru all sparkplug holes, reinstalled the head & installed new plugs - all good, Thanks for the advice

 

[Bayless]

Glad to hear it worked out for you.